Patent Publication Number: US-2021193274-A1

Title: Method for searching compound, program for searching compound, recording medium, and device for searching compound

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of PCT International Application No. PCT/JP2019/036074 filed on Sep. 13, 2019 claiming priority under 35 U.S.C § 119(a) to Japanese Patent Application No. 2018-172578 filed on Sep. 14, 2018. Each of the above applications is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for searching a compound, a program for searching a compound, a recording medium, and a device for searching a compound, and particularly relates to a technique for searching a structure of a compound having a desired physical property value. 
     2. Description of the Related Art 
     In the related art, the search for a structure of a compound having a desired physical property value has been performed mainly by solving a “forward problem” (giving a molecular structure as a cause of the problem and obtaining a physical property value as a result), but with the development of informatics in recent years, studies on a solution method of an “inverse problem” (giving a physical property value and obtaining a molecular structure having the physical property value) are rapidly progressing. For example, “Bayesian molecular design with a chemical language model”, Hisaki Ikebata et al., “searched on Jul. 23, 2018”, internet (https://www.ncbi.nlm.nih.gov/pubmed/28281211) is known for searching for a structure by solving the inverse problem. The “Bayesian molecular design with a chemical language model”, Hisaki Ikebata et al., “searched on Jul. 23, 2018”, internet (https://www.ncbi.nlm.nih.gov/pubmed/28281211) discloses that a structure having a physical property value close to the target value is obtained by, giving a target value of physical property value, (1) generating a plurality of initial structures (chemical structures), (2) randomly changing each structure, (3) estimating the physical property value of each structure, and (4) adopting or rejecting the change in structure based on the distance between the physical property value and the target value (in this process, the processes ( 2 ) to ( 4 ) are repeated). 
     SUMMARY OF THE INVENTION 
     The Inverse Quantitative Structure-Property Relationship (iqspr) disclosed in the “Bayesian molecular design with a chemical language model”, Hisaki Ikebata et al., “searched on Jul. 23, 2018”, internet (https://www.ncbi.nlm.nih.gov/pubmed/28281211) has a problem that the search efficiency is immediately lowered. For example,  FIG. 21  is a diagram showing search results of a compound having a first excitation energy (57.2 kcal/mol) corresponding to a wavelength of 500 nm (mean values of top 100 compounds in each trial calculated by ZINDO using a quantum chemistry calculation software “Gaussian16” is plotted). In the iqspr, as shown in  FIG. 21 , the search quickly falls into a local minimum (state in which the physical property value moves away from the target value no matter how the structure is minutely changed), which slows the search. The cause of this slow search lies in a structural update algorithm (particulate filter based on Bayesian inference).  FIGS. 22A to 22C  are conceptual diagrams showing the algorithm of the particulate filter, and in a case where weight is calculated based on the physical property value from an initial state shown in  FIG. 22A , a state shown in  FIG. 22B  is obtained. In a case where sampling with replacement is performed from this state based on the weight (extraction of the same structure is accepted), as shown in  FIG. 22C , the structures C and D in which physical property values move away from the target are removed. 
     In addition,  FIG. 23  is a table showing an example of the relationship between the initial structural formula of the compound (left column) and the structural formula of the 10th trial (right column), and shows a state in which all the structures are similar as the trials are repeated even though various structures are given in the initial state. As shown in  FIGS. 21 to 23 , in the structural update based on Bayesian inference, although the physical property value approaches the target value, the diversity of structures for search is reduced, the search falls into the local minimum, and even in a case where the trial is repeated, it is not possible to escape from the local minimum state (it is not possible to reach the final structure). 
     As described above, in the technique in the related art, it is not possible to efficiently search for the structure of the compound. 
     The present invention has been studied in view of such circumstances, and an object of the present invention is to provide a method for searching a compound, a program for searching a compound, a recording medium, and a device for searching a compound, which are capable of efficiently searching a structure of a compound. 
     In order to achieve the above-described object, a method for searching a compound according to a first aspect of the present invention includes: 
     an input step of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition step of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation step of calculating the physical property value of the candidate structure; 
     a candidate structure adoption step in which the candidate structure is adopted or rejected, including,
         performing a first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure,   in a case where the candidate structure is not adopted by the first adoption process, performing a second adoption process to determine whether to or not to adopt the candidate structure based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure, and   in a case where the candidate structure is not adopted by the first adoption process and the second adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control step of repeating the processes in the input step, the candidate structure acquisition step, the physical property value calculation step, and the candidate structure adoption step until a termination condition is satisfied. 
     In the first aspect, because of performing the first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure, in a case where the candidate structure is not adopted as a result of the first adoption process, performing the second adoption process to determine the adoption based on whether or not the structural diversity increases, and in a case where the candidate structure is not adopted as a result of the first adoption process and the second adoption process, performing the rejection process to reject the change in chemical structure and return to the chemical structure before the change, it is possible to promote escape from the local minimum based on the diversity of structures, and efficiently search for the structure of the compound having a desired physical property value (target value). 
     In the first aspect and each aspect, the “chemical structure” includes a structure (initial structure) in an initial state, and also includes a structure in which the initial structure is changed by repeating the processes. 
     In order to achieve the above-described object, a method for searching a compound according to a second aspect of the present invention includes: 
     an input step of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition step of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation step of calculating the physical property value of the candidate structure; 
     a candidate structure adoption step in which the candidate structure is adopted or rejected, including,
         performing a second adoption process to determine whether to or not to adopt the candidate structure based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure,   in a case where the candidate structure is not adopted by the second adoption process, performing a first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure, and   in a case where the candidate structure is not adopted by the first adoption process and the second adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control step of repeating the processes in the input step, the candidate structure acquisition step, the physical property value calculation step, and the candidate structure adoption step until a termination condition is satisfied. 
     In the second aspect, the second adoption process to determine whether to or not to adopt the candidate structure based on whether or not the structural diversity of the structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure is performed; in a case where the candidate structure is not adopted by the second adoption process, the first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure is performed; and in a case where the candidate structure is not adopted by the first adoption process and the second adoption process, the rejection process to reject the change in chemical structure and return to the chemical structure before the change is performed. That is, the order of the first and second adoption processes is different from that of the first aspect (the details of the first and second adoption processes are the same as those in the first aspect). Even in a case of such an aspect, as in the first aspect, it is possible to promote escape from the local minimum based on the diversity of structures, and efficiently search for the structure of the compound having a desired physical property value (target value). 
     A method for searching a compound according to a third aspect includes that, 
     in the first aspect or the second aspect, as the first adoption process in the candidate structure adoption step, in a case where an absolute value of a difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value is equal to or less than an absolute value of a difference (second difference) between the physical property value of the chemical structure and the target value of the physical property value, a process of adopting the candidate structure is performed, and 
     in a case where the absolute value of the difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value is more than the absolute value of the difference (second difference) between the physical property value of the chemical structure and the target value of the physical property value, a process of calculating a first adoption probability from a first function based on the difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value and adopting the candidate structure with the first adoption probability is performed. In the third aspect, the case where the absolute value of the first difference is equal to or less than the absolute value of the second difference is a case where the physical property value does not move away from the target value due to the change in structure, thereby adopting the candidate structure. On the other hand, the case where the absolute value of the first difference is more than the absolute value of the second difference is a case where the physical property value moves away from the target value due to the change in structure, thereby adopting the first adoption probability. 
     A method for searching a compound according to a fourth aspect includes that, 
     in the third aspect, the first function is a monotonically decreasing function with respect to a difference (third difference) between the absolute value of the difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value, and the absolute value of the difference (second difference) between the physical property value of the chemical structure and the target value of the physical property value. In the fourth aspect, since the first function is a monotonically decreasing function with respect to the third difference, as the third difference is larger (that is, as the physical property value further moves away from the target value due to the change in structure), the adoption probability is lowered. 
     In order to achieve the above-described object, a method for searching a compound according to a fifth aspect of the present invention includes: 
     an input step of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition step of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation step of calculating the physical property value of the candidate structure; 
     a candidate structure adoption step in which the candidate structure is adopted or rejected, including,
         performing a first calculation process, in which a first adoption probability used for adopting the candidate structure is calculated based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure, and a second calculation process, in which a second adoption probability used for adopting the candidate structure is calculated based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure,   performing an adoption process to adopt the candidate structure based on the first adoption probability and the second adoption probability, and   in a case where the candidate structure is not adopted as a result of the adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control step of repeating the processes in the input step, the candidate structure acquisition step, the physical property value calculation step, and the candidate structure adoption step until a termination condition is satisfied. 
     The fifth aspect is different from the first and second aspects in that the first and second calculation processes are performed simultaneously, and the candidate structure is adopted based on the first and second adoption probabilities. Even in a case of such an aspect, as in the first and second aspects, it is possible to promote escape from the local minimum based on the diversity of structures, and efficiently search for the structure of the compound having a desired physical property value (target value). 
     A method for searching a compound according to a sixth aspect includes that, 
     in the candidate structure adoption step in the fifth aspect, in a case where an absolute value of a difference between the physical property value of the candidate structure and the target value of the physical property value is equal to or less than an absolute value of a difference between the physical property value of the chemical structure and the target value of the physical property value, a process of adopting the candidate structure is performed, and 
     in a case where the absolute value of the difference between the physical property value of the candidate structure and the target value of the physical property value is more than the absolute value of the difference between the physical property value of the chemical structure and the target value of the physical property value, a process of calculating the first adoption probability from a first function based on the difference between the physical property value of the candidate structure and the target value of the physical property value, and a process of calculating an increase or decrease amount in the structural diversity of the structural group and calculating the second adoption probability from a second function based on the increase or decrease amount are performed. 
     A method for searching a compound according to a seventh aspect includes that, 
     in the candidate structure adoption step in the fourth or sixth aspect, a difference between a structural diversity of a first structural group composed of chemical structures before the change and a structural diversity of a second structural group composed of chemical structures after at least one change is calculated as the increase or decrease amount. 
     A method for searching a compound according to an eighth aspect includes that, 
     in the candidate structure adoption step in the fourth or sixth aspect, a difference between a structural diversity of a first structural group including at least a part of structural groups after at least one change and a structural diversity of a second structural group obtained by adding the candidate structure to the first structural group is calculated as the increase or decrease amount. 
     A method for searching a compound according to a ninth aspect includes that, 
     in the third or sixth aspect, the first function is a monotonically decreasing function with respect to the difference between the absolute value of the difference between the physical property value of the candidate structure and the target value of the physical property value, and the absolute value of the difference between the physical property value of the chemical structure and the target value of the physical property value. 
     A method for searching a compound according to a tenth aspect includes that, 
     in the fourth or sixth aspect, the second function is a monotonically increasing function with respect to the increase or decrease amount in the structural diversity. 
     A method for searching a compound according to an eleventh aspect includes that, 
     in the candidate structure acquisition step in any one of the first to tenth aspects, an atom or an atomic group is added to or deleted from the chemical structure to generate an objective structure, and the objective structure is defined as the candidate structure. The eleventh aspect defines a method for generating an objective structure. The addition or deletion may be performed in a unit of one atom, or in a unit of an atomic group (group of two or more atoms). 
     A method for searching a compound according to a twelfth aspect includes that, 
     in the control step in any one of the first to eleventh aspects, the termination condition is determined to be satisfied in a case where the number of times that the chemical structure is changed reaches a specified number of times and/or a case the physical property value of the candidate structure reaches the target value, and the processes of the input step, the candidate structure acquisition step, the physical property value calculation step, and the candidate structure adoption step are terminated. The twelfth aspect specifically defines the termination condition. 
     In order to achieve the above-described object, a program for searching a compound according to a thirteenth aspect of the present invention causes a computer to execute the method for searching a compound according to any one of the first to twelfth aspects. According to the thirteenth aspect, by the method for searching a compound according to any one of the first to twelfth aspects, it is possible to efficiently search for the structure of the compound having a desired physical property value. The “computer” in the thirteenth aspect can be realized by using one or more various processors such as a central processing unit (CPU). 
     In order to achieve the above-described object, a non-temporary and computer-readable recording medium according to a fourteenth aspect of the present invention causes a computer to execute the program according to the thirteenth aspect in a case where a command stored in the recording medium is read by the computer. The recording medium according to the fourteenth aspect can be realized by recording a computer-readable code of the program according to the thirteenth aspect. 
     In order to achieve the above-described object, a device for searching a compound according to a fifteenth aspect of the present invention includes: 
     an input part of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition part of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation part of calculating the physical property value of the candidate structure; 
     a candidate structure adoption part in which the candidate structure is adopted or rejected, including,
         performing a first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure,   in a case where the candidate structure is not adopted by the first adoption process, performing a second adoption process to determine whether to or not to adopt the candidate structure based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure, and   in a case where the candidate structure is not adopted by the first adoption process and the second adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control part of repeating the processes in the input part, the candidate structure acquisition part, the physical property value calculation part, and the candidate structure adoption part until a termination condition is satisfied. According to the fifteenth aspect, as the first aspect, it is possible to efficiently search for the structure of the compound having a desired property. The device for searching a compound according to the fifteenth aspect may further include the same configurations as in the third to fourth, and seventh to twelfth aspects. 
     In order to achieve the above-described object, a device for searching a compound according to a sixteenth aspect of the present invention includes: 
     an input part of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition part of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation part of calculating the physical property value of the candidate structure; 
     a candidate structure adoption part in which the candidate structure is adopted or rejected, including,
         performing a second adoption process to determine whether to or not to adopt the candidate structure based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure,   in a case where the candidate structure is not adopted by the second adoption process, performing a first adoption process to determine whether to or not to adopt the candidate structure based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure, and   in a case where the candidate structure is not adopted by the first adoption process and the second adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control part of repeating the processes in the input part, the candidate structure acquisition part, the physical property value calculation part, and the candidate structure adoption part until a termination condition is satisfied. According to the sixteenth aspect, as the second aspect, it is possible to efficiently search for the structure of the compound having a desired property. The device for searching a compound according to the sixteenth aspect may further include the same configurations as in the third to fourth, and seventh to twelfth aspects. 
     In order to achieve the above-described object, a device for searching a compound according to a seventeenth aspect of the present invention includes: 
     an input part of inputting a chemical structure of one or more compounds, one or more physical property values according to the chemical structure, and a target value of the physical property values; 
     a candidate structure acquisition part of acquiring a candidate structure by changing the chemical structure; 
     a physical property value calculation part of calculating the physical property value of the candidate structure; 
     a candidate structure adoption part in which the candidate structure is adopted or rejected, including,
         simultaneously performing a first calculation process, in which a first adoption probability of adopting the candidate structure is calculated based on whether or not the physical property value of the candidate structure approaches the target value of the physical property value due to the change in chemical structure, and a second calculation process, in which a second adoption probability of adopting the candidate structure is calculated based on whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure,   performing an adoption process to adopt the candidate structure based on the first adoption probability and the second adoption probability, and   in a case where the candidate structure is not adopted as a result of the adoption process, performing a rejection process to reject the change in chemical structure and return to the chemical structure before the change; and       

     a control part of repeating the processes in the input part, the candidate structure acquisition part, the physical property value calculation part, and the candidate structure adoption part until a termination condition is satisfied. According to the seventeenth aspect, as the fifth aspect, it is possible to efficiently search for the structure of the compound having a desired property. The device for searching a compound according to the seventeenth aspect may further include the same configurations as in the sixth to twelfth aspects. 
     As described above, according to the method for searching a compound, program for searching a compound, recording medium, and device for searching a compound of the present invention, it is possible to efficiently search for the structure of the compound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a device for searching a compound according to a first embodiment. 
         FIG. 2  is a block diagram showing a configuration of a processing part. 
         FIG. 3  is a flowchart showing a procedure of a method for searching a compound. 
         FIGS. 4A to 4D  are diagrams showing changes in chemical structure in the examples. 
         FIG. 5  is a diagram showing a chemical structural group before and after the change. 
         FIG. 6  is a diagram showing a calculation result of an extended fingerprint for the chemical structure before and after the change. 
         FIG. 7  is a diagram explaining a diversity of structures. 
         FIG. 8  is a diagram showing how the change in structure is adopted. 
         FIG. 9  is a diagram showing how the change in structure is rejected. 
         FIG. 10  is a diagram showing an evaluation result of the change in structure in the structural group. 
         FIG. 11  is a diagram showing a chemical structure having a physical property value closest to a target value. 
         FIG. 12  is a diagram showing how the chemical structure changes as the process is repeated. 
         FIGS. 13A and 13B  are diagrams showing other chemical structures having the target physical property value. 
         FIG. 14  is a diagram showing search results according to Bayesian inference and the present invention. 
         FIGS. 15A and 15B  are diagrams showing how  2 \,max changes according to Bayesian inference and the present invention. 
         FIG. 16  is a diagram showing a structural diversity according to Bayesian inference and the present invention. 
         FIG. 17  is a diagram showing the number of trials required to achieve a target for two diversity evaluation methods. 
         FIG. 18  is a table showing results of structural search in a case where methyl yellow is included in a comparative target of the diversity. 
         FIG. 19  is a flowchart showing a procedure of a method for searching a compound according to a second embodiment. 
         FIG. 20  is a flowchart showing a procedure of a method for searching a compound according to a third embodiment. 
         FIG. 21  is a diagram showing how to fall into a local minimum in the related art. 
         FIGS. 22A to 22C  are diagrams of how the diversity of structures is reduced in the related art. 
         FIG. 23  is a diagram showing a state in which the diversity of structures is reduced in the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of a method for searching a compound, program for searching a compound, recording medium, and device for searching a compound according to the present invention will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a block diagram showing a configuration of a device  10  for searching a compound (device for searching a compound) according to a first embodiment. As shown in  FIG. 1 , the device  10  for searching a compound includes a processing part  100 , a storage part  200 , a display part  300 , and an operation part  400 , which are connected to each other to transmit and receive necessary information. Various installation forms can be adopted for these constituents, and each constituent may be installed in one place (one housing, one room, and the like), or may be installed at a distant place and connected through a network. In addition, the device  10  for searching a compound is connected to an external server  500  and an external database  510  through a network  1000 , and can acquire necessary information such as input data. 
     &lt;Configuration of Processing Part&gt; 
       FIG. 2  is a diagram showing a configuration of a processing part  100 . The processing part  100  includes an input part  102  (input part), a candidate structure acquisition part  104  (candidate structure acquisition part), a physical property value calculation part  106  (physical property value calculation part), a candidate structure adoption part  108  (candidate structure adoption part), a control part  110  (control part), a display control part  112  (display control part), a central processing unit (CPU)  120  (CPU), a read only memory (ROM)  122  (ROM), and a random access memory (RAM)  124  (RAM). The procedure of the method for searching a compound using each part of the processing part  100  will be described in detail later. The process in each part is performed under the control of the CPU  120 . 
     The function of each part of the processing part  100  described above can be realized by using various processors. Examples of the various processors include a CPU that is a general-purpose processor which executes software (program) to realize various functions. In addition, examples of the various processors also include a graphics processing unit (GPU) which is a processor specializing in image process and a programmable logic device (PLD) which is a processor in which circuit configuration can be changed after manufacturing, such as a field programmable gate array (FPGA). Furthermore, examples of the various processors also include a dedicated electric circuit which is a processor having a circuit configuration specifically designed to execute a specific process, such as an application specific integrated circuit (ASIC). 
     The functions of each part may be realized by one processor, or may be realized by a plurality of processors of the same type or different types (for example, a plurality of FPGAs, a combination of CPU and FPGA, or a combination of CPU and GPU). In addition, a plurality of functions may be realized by one processor. As an example of configuring a plurality of functions with one processor, firstly, an aspect that, as typified by a computer such as a client and a server, one processor is configured by a combination of one or more CPUs and software, and this processor realizes the plurality of functions is exemplified. Secondly, an aspect that, as typified by a system on chip (SoC), uses a processor which realizes the functions of the entire system with a single integrated circuit (IC) chip is exemplified. As described above, various functions are composed by using one or more of the above-described various processors as a hardware structure. Furthermore, the hardware structure of these various processors is more specifically an electric circuit (circuitry) in which circuit elements such as semiconductor elements are combined. This electric circuit may be an electric circuit which realizes the above-described functions by using logical sum, logical product, logical negation, exclusive logical sum, and logical operation of a combination thereof 
     In a case where the above-described processor or electric circuit executes a software (program), a processor-readable code (computer-readable code) of the software to be executed is stored in a non-temporary recording medium (recording medium) such as ROM  122  (see  FIG. 2 ), and the processor refers to the software. The software stored in the non-temporary recording medium includes the program (program for searching a compound) for executing the method for searching a compound according to the embodiment of the present invention, and in a case where a command stored in the recording medium is read by the computer, the command causes the computer to execute the program for searching a compound. The code may be recorded in a non-temporary recording medium such as various magneto-optical recording devices and semiconductor memories instead of ROM  122 . In a case of processing using a software, for example, RAM  124  is used as a temporary storage area, and for example, data stored in an electronically erasable and programmable read only memory (EEPROM) (not shown) can be referred to. 
     &lt;Configuration of Storage Part&gt; 
     The storage part  200  is configured of a non-temporary recording medium such as a digital versatile disk (DVD), a hard disk, and various semiconductor memories, and a control part thereof, and can store the chemical structure (initial structure and candidate structure) of the compound, a physical property value thereof, and the like. 
     &lt;Configuration of Display Part and Operation Part&gt; 
     The display part  300  includes a monitor  310  (display device), and can display the input image, the information stored in the storage part  200 , the result of process by the processing part  100 , and the like. The operation part  400  includes a keyboard  410  and a mouse  420  as input devices and/or pointing devices, and the user can perform operations necessary for executing the method for searching a compound according to the embodiment of the present invention through these devices and a screen of the monitor  310 . For example, the user can perform designation of process start instruction, target value of physical property value, parameters used for the first function and the second function, and number of repetitions. 
     &lt;Procedure of Method for Searching Compound&gt; 
       FIG. 3  is a flowchart showing a procedure of the method for searching a compound according to the embodiment of the present invention. 
     &lt;Data Input&gt; 
     The input part  102  inputs a chemical structure (initial structure) of one or more compounds, one or more physical property values according to the chemical structure (initial structure), and a target value of the physical property values (Step S 1010 : input step). Data stored in the storage part  200  may be used as these data, or these data may be acquired from the external server  500  and the external database  510  through the network  1000 . What kind of data may be input may be decided according to the user&#39;s instruction input through the operation part  400 . The initial structure may be one or a plurality. In addition, the physical property value may also be one or a plurality. As a method for giving physical property values, a method with high throughput, such as quantum chemistry calculation, molecular dynamics calculation, and machine learning result, is desirable. On the other hand, in a case where there is no practical problem in the throughput of compound synthesis or physical property measurement, it is possible to use the measured value. 
     &lt;Acquisition of Candidate Structure&gt; 
     The candidate structure acquisition part  104  randomly changes the chemical structure to acquire a candidate structure (Step S 1020 : candidate structure acquisition step). In this case, any method which can change the chemical structure may be used. For example, a method in which an atom or an atomic group is added to or deleted from the chemical structure to generate an objective structure, and the objective structure is defined as the candidate structure can be used. Specifically, this method is a method for generating a compound structure, which includes (A) a step of preparing a standard compound database for evaluating synthetic aptitude and a compound structure (chemical structure), (B) a step of choosing to add an atom or an atomic group to the compound structure or to delete an atom from the compound structure, (C) a step of, in a case of choosing to add an atom to the compound structure, bonding a new atom to an atom selected from atoms included in the compound structure, or in a case of choosing to delete an atom from the compound structure, deleting selected atom from the atoms included in the compound structure, thereby obtaining a modified compound structure, (D) a step of determining a synthetic aptitude of the modified compound structure based on information of the compound database, (E) a step of, in a case where the modified compound structure has the synthetic aptitude, probabilistically accepting the modification, or in a case where the modified compound structure does not have the synthetic aptitude, probabilistically rejecting the modification, and (F) a step of repeating the steps (B) to (E) until the compound structure which has undergone the step (E) satisfies a termination condition. The generated candidate structure may be displayed on the monitor  310  (display device) by the display control part  112 . In addition, in a case of returning to the step S 1020  from the step S 1090  described later, it is also possible to add one or more structures among structures generated last time, in which physical property values are close to the target value, to the compound database (structural group) for evaluating the synthetic aptitude, and in the step S 1020 , gradually generate a structure having a physical property value close to the target value. 
     &lt;Evaluation of Physical Property Value&gt; 
     The physical property value calculation part  106  calculates a physical property value of the candidate structure (structure changed in the step S 1020 ) (Step S 1030 : physical property value calculation step). For the calculation of the physical property value, it is preferable to use the same method as a case of estimating the physical property value of the initial structure. 
     &lt;First Adoption Process&gt; 
     The candidate structure adoption part  108  determines whether or not the physical property value approaches the target value (Step S 1040 : candidate structure adoption step). Specifically, in a case where a physical property value before the change in structure is defined as f0, a physical property value after the change in structure is defined as f1, and the target value of the physical property value is defined as F, in a case where |F−f1|≤|F−f0| is satisfied (a case where the absolute value of the difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value is equal to or less than the absolute value of the difference (second difference) between the physical property value of the chemical structure and the target value of the physical property value), since the physical property value approaches (does not move away from) the target value, the process proceeds to a step S 1070  to adopt the change in structure (first adoption process). On the other hand, in a case where |F−f1|&gt;|F−f0| is satisfied (a case where the absolute value of the difference (first difference) between the physical property value of the candidate structure and the target value of the physical property value is more than the absolute value of the difference (second difference) between the physical property value of the chemical structure and the target value of the physical property value), the process proceeds to a step S 1050 . 
     In the step S 1050  (candidate structure adoption step), the candidate structure adoption part  108  calculates a first adoption probability from a first function based on the difference between the physical property value of the candidate structure and the target value of the physical property value (first adoption process). Specifically, the candidate structure adoption part  108  gives a monotonically decreasing function P1(d) in which d=|F−f1|−|F−f0|, and estimates a probability p1=P1(d). The monotonically decreasing function P1(d) corresponds to the “first function” (monotonically decreasing function with respect to the difference between the absolute value of the difference between the physical property value of the candidate structure and the target value of the physical property value, and the absolute value of the difference between the physical property value of the chemical structure and the target value of the physical property value) in the present invention, and the probability p1 corresponds to the “first adoption probability” in the present invention. 
     Various functions can be used as the monotonically decreasing function P1(d), and for example, a function represented by Expression (1) can be used.  6  is a hyperparameter, and the degree of monotonous decrease can be adjusted by changing the value of 6. The value of parameter may be changed by inputting the user&#39;s instruction through the operation part  400 . 
         P   1 ( d )=exp[− d /σ]  (1)
 
     In a case of n objective (where the number of physical property values input in the step S 1010  is n), defining i as an index representing each objective, for example, functions represented by Expressions (2) and (3) can be used. 
     
       
         
           
             
               
                 
                   
                     w 
                     i 
                   
                   = 
                   
                     exp 
                      
                     
                       [ 
                       
                         
                           - 
                           
                             d 
                             i 
                           
                         
                          
                         
                           / 
                         
                          
                         
                           σ 
                           i 
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       P 
                       1 
                     
                      
                     
                       ( 
                       
                         { 
                         
                           d 
                           i 
                         
                         } 
                       
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             1 
                              
                             
                                 
                             
                           
                         
                         
                           
                             ( 
                             
                               ∃ 
                               
                                 
                                   is 
                                   . 
                                   t 
                                   . 
                                   
                                     w 
                                     i 
                                   
                                 
                                 &gt; 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             
                               ∏ 
                               
                                 i 
                                 = 
                                 1 
                               
                               n 
                             
                              
                             
                                 
                             
                              
                             
                               w 
                               i 
                             
                           
                         
                         
                           
                             ( 
                             otherwise 
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The functions represented by Expressions (2) and (3) are based on the criterion that “in a case where there is even one physical property value which approaches the target, adopting the change in structure”, but various other functions can be used. In addition, more simply, in a case of considering the physical property value of the n object as n-dimensional vectors ff and FF, it is also possible to estimate d=|FF−ff1|−|FF−ff0| from Euclidean distance |FF−ff| so that the case is solved as a single-object problem (it is assumed that ff, ff0, ff1, and FF are vectors). In a case of adopting this policy, it is desirable to calculate the average and variance of each physical property value from the existing data, perform standardization, and then calculate the distance. 
     After obtaining the probability p1, the candidate structure adoption part  108  uses an appropriately generated random number to proceed to the step S 1070  with the probability p1, adopt the change in structure, and proceed to a step S 1055  with a probability (1−p1). That is, in the step S 1050 , the candidate structure adoption part  108  adopts the candidate structure with the first adoption probability (first adoption process). The reason why the probabilistic process is performed in this way (even in a case where the physical property value moves away from the target value, the change in structure is adopted with the probability p1) is to prevent a drop to a local minimum. The local minimum means “state in which the physical property value moves away from the target value no matter how the structure is changed”, and in order to escape from the local minimum and reach a global minimum, it is necessary to undergo a change in structure in which the physical property value moves away from the target value. By the above-described probabilistic process, such a path can be secured. 
     &lt;Second Adoption Process&gt; 
     In a case where the candidate structure is not adopted as a result of the first adoption process in the step S 1050  (possible with the probability (1−p1)), the candidate structure adoption part  108  performs a second adoption process to determine whether to or not to adopt the candidate structure based on “whether or not a structural diversity of a structural group composed of the chemical structure and the candidate structure increases due to the change in chemical structure” (Steps S 1055 , S 1060 , and S 1070 ). The second adoption process will be described below. The index representing the structure is defined as j, and the structural group is represented by S={sj}. A function which gives the structural diversity of a structural group S is expressed as V(S). It is assumed that V(S) takes a larger value as the structural diversity increases. 
     &lt;Evaluation Method of Structural Diversity (1)&gt; 
     In a case of giving N (&gt;1) initial structures, it is assumed that the change in structure of kth chemical structure among the N chemical structures is adopted or rejected. In mth trial, from a structural group Sm−1={s(m−1)j} before a change in structure (m-lth) and a structural group Sm={smj} after the change (mth), a structural group Sk={s(m−1)0, s(m−1)1, . . . , smk, . . . , s(m−1)N} after the change in structure of the kth chemical structure is defined, and dv=V(Sk)−V(Sm−1) is estimated. dv indicates an increase or decrease amount in the structural diversity due to changes in structure. In a case where dv&gt;0 (a case where the diversity is improved by the kth change in structure; Yes in the step S 1055 ), a monotonically increasing function P2(dv) with respect to dv (increase or decrease amount in the structural diversity) is given, and a probability p2=P2(dv) is calculated (Step S 1060 : second adoption process). Then, using an appropriately generated random number, the process proceeds to the step S 1070  (adopting the change in structure; second adoption process) with the probability p2, and proceeds to a step S 1080  (rejecting the change in structure and returning to the original structure; rejection process) with a probability (1−p2). The monotonically increasing function P2(dv) corresponds to the “second function” in the present invention, and the probability p2 corresponds to the “second adoption probability” in the present invention. 
     The reason why the above-described probabilistic process (calculating the candidate structure with the probability p2 calculated by the monotonically increasing function P2(dv)) is performed in a case where the structural diversity increases is that, in a case of setting to “always adopt the change in structure in a case where the structural diversity increases”, the change in structure is adopted too frequently even though the physical property value moves away from the target value, and as a result, the convergence of the physical property value to the target value may be delayed. By performing the above-described probabilistic process, the convergence of the physical property value can be accelerated and the structure of the compound can be efficiently searched. 
     In a case where dv&lt;0 calculated in the step S 1060  (a case where the diversity decreases; No in the step S 1055 ), the process proceeds to the step S 1080  (rejecting the change in structure and returning to the original structure; rejection process). 
     &lt;Evaluation Method of Structural Diversity (2)&gt; 
     Instead of the above-described “evaluation method of structural diversity (1)”, the probability p2 may be calculated (Step S 1060 : second adoption process) by the monotonically increasing function P2(dv) assuming that, in a case where an index representing the trial is defined as t, a structural group Sprev={St-1, St-2, . . . , St-m} (here, S0 shown in a case where t=m is defined as the initial structure) obtained in the past m trials and a structural group Scurr={st, St-1, . . . , St-(m-1)} to which a structure st that is considered to be adopted or rejected is added are defined, and dv=V(Scurr)−V(Sprev) is calculated. That is, the structural group Sprev is a structural group (first structural group) composed of the initial structure and chemical structures after at least one change, and the structural group Scurr is a structural group (second structural group) in which the candidate structure is added to the first structural group. Sprev (first structural group) may include the initial structure and at least a part of structural groups after at least one change. In addition, V(Sprev) and V(Scurr) are respectively the structural diversity of the structural groups Sprev and Scurr, and dv indicates an increase or decrease amount in the structural diversity due to changes in structure. In addition, in addition to the case where all the initial structure and structural groups obtained in past trials are used, structures of the higher performance (ranking is higher as the physical property value is closer to the target value) or the lower performance (ranking is lower as the physical property value is farther from the target value) may be extracted and used as Sprev, or compounds from existing library (compounds of known structures) may be mixed with Sprev. By selecting Sprev in this way, it is possible to flexibly set the evaluation standard for structural diversity. 
     In the “evaluation method of structural diversity (2)”, it is easy to select a candidate structure different from the chemical structure included in Sprev which is the evaluation standard for diversity. For example, in a case where the compounds from existing library (compounds of known structures) are included in Sprev, a candidate structure with low structural similarity to the “compounds from existing library” (having a different structure from known compounds) can be easily selected. In addition, in a case where the structures with higher performance (having physical property values close to the target value) are extracted and used as Sprev, it is easy to select “a structure with higher performance, which has a structural feature different from the structure with higher performance already covered”. Therefore, this condition can be specified in a case where it is desired to acquire as many structures with higher performance as possible. In addition, even in a case where existing library compounds with higher performance are difficult to use for some reason (easy to decompose, toxic, and the like), these can be added to Sprev to perform the structural search. On the other hand, in a case where the structures with lower performance are extracted and used as Sprev, it is easy to select “a structure with higher performance, which has a structural feature different from the structure with lower performance already covered”. The diversity of the structural group of structures with higher performance, obtained by this search, may be lower than that of a case where the structures with higher performance are extracted, but since the search proceeds so as to avoid the structure with lower performance, it is considered that the search itself can be accelerated. As described above, the structure finally obtained may differ depending on how Sprev is selected. 
     &lt;Function which Gives Structural Diversity of Structural Group&gt; 
     As the above-described “function which gives the structural diversity of the structural group”, for example, the following definition can be considered based on Tanimoto coefficient (one of indexes showing similarity of compounds) (various other definitions are possible). Specifically, in a case where a structure s as a fingerprint (the compound is converted into a fixed-length vector according to a certain rule, and various production methods are known) of a bit stream (sequence of 0 or 1) is defined as Fs, the definition of the Tanimoto coefficient is represented by Expression (4). 
     
       
         
           
             
               
                 
                   
                     T 
                     
                       s 
                       , 
                       
                         s 
                         ′ 
                       
                     
                   
                   = 
                   
                     
                       T 
                        
                       
                         ( 
                         
                           
                             F 
                             s 
                           
                           , 
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                          
                         
                           
                             F 
                             s 
                           
                           ⋂ 
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                         
                          
                       
                       
                         
                            
                           
                             F 
                             s 
                           
                            
                         
                         + 
                         
                            
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                            
                         
                         - 
                         
                            
                           
                             
                               F 
                               s 
                             
                             ⋂ 
                             
                               F 
                               
                                 s 
                                 ′ 
                               
                             
                           
                            
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Here, |Fs| is the number of bits of 1 in Fs, and |Fs∩Fs′| is the number of bits of 1 in common between Fs and Fs′. Ts,s′ is 1 in a case where Fs and Fs&#39; are completely matched, and is 0 in a case where Fs and Fs&#39; are not completely matched. Therefore, Ts,s′ is an index showing the similarity between the structure s and the structure s′. Since it is the dissimilarity to be obtained, the dissimilarity vs,s′ between the structure s and the structure ‘s is defined by Expression (5). 
         v   S,S′ =1− T   S,S′   (5)
 
     Using this dissimilarity vs,s′, the dissimilarity of the structural group S (that is, the structural diversity of the structural group) can be defined by Expression (6). 
     
       
         
           
             
               
                 
                   
                     V 
                      
                     
                       ( 
                       S 
                       ) 
                     
                   
                   = 
                   
                     
                       2 
                       
                         N 
                          
                         
                           ( 
                           
                             N 
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                      
                     
                       
                         ∑ 
                         
                           
                             s 
                             ∈ 
                             S 
                           
                           , 
                           
                             
                               s 
                               ′ 
                             
                             ∈ 
                             S 
                           
                           , 
                           
                             s 
                             ≠ 
                             
                               s 
                               ′ 
                             
                           
                         
                       
                        
                       
                         v 
                         
                           s 
                           , 
                           
                             s 
                             ′ 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     V(S) takes a value from 0 to 1, and the structural diversity of the structural group is higher as the value is larger. 
     In addition, as the monotonically increasing function P2(dv) with respect to the increase or decrease amount dv of the structural diversity, a function represented by Expression (7) can be used. σv and Cv are hyperparameters, and the degree of monotonous increase can be adjusted by changing the values thereof. The values of these parameters may be changed by inputting the user&#39;s instruction through the operation part  400 . 
         P   2 ( d   v )= C   v (1−exp[− d   v /σ v ])  (7)
 
     Obviously from the functional form, P2 is Cv at the limit of dv→∞. Therefore, Cv means “probability in which the change in structure is adopted in a case of the change in structure that the diversity is sufficiently improved”. 
     &lt;Repetition of Process&gt; 
     One trial terminates in a case where the above-described first adoption process, second adoption process, and rejection process are performed for each of the given initial structures, and the above-described processes terminate for all chemical structures. 
     In a case where the candidate structure is adopted or rejected as a result of the above-described first adoption process, second adoption process, and rejection process, the control part  110  determines whether or not the termination condition is satisfied (Step S 1090 : control step). For example, in a case where the number of times changing the chemical structure (the number of trials) reaches a specified number of times, and/or a case where the physical property value of the candidate structure reaches the target value, it can be determined that “the termination condition is satisfied”. In a case of calculating a plurality of chemical structures and/or physical property values, it may be determined that “in a case where there is even one chemical structure and/or physical property value which has reached the target value, the calculation is terminated”, or may be determined to “repeat trials until all structure and/or physical property values reach the target”. The control part  110  repeats the processes (input step, candidate structure acquisition step, physical property value calculation step, and candidate structure adoption step) from the step S 1020  to the step S 1080  unit the termination condition is satisfied (No in the step S 1090 ), and terminates the process of the method for searching a compound in a case where the termination condition is satisfied (Yes in the step S 1090 ) (Step S 1100 ). 
     &lt;Effect of First Embodiment&gt; 
     As described above, according to the device  10  for searching a compound according to the first embodiment, a method for searching a compound, recording medium, and a program for searching a compound, since the escape from the local minimum can be promoted and the convergence of the physical property value can be accelerated, the structure of the compound having a desired physical property value can be efficiently searched. 
     &lt;Examples: Search for Coloring Agent&gt; 
     The present invention will be specifically described with reference to the example. Even in this example, the search can be performed by the device  10  for searching a compound (device for searching a compound) shown in  FIGS. 1 and 2  and the flowchart (method for searching a compound and process of the program for searching a compound) shown in  FIG. 3 . 
     &lt;Input Step&gt; 
     In the example, as shown in  FIG. 4A , 25 phenols are given as an initial structure. Considering λmax (maximum absorption wavelength) as a physical property value, a target value is set to 367 nm. The structure was optimized with PM6 level, and then λmax is calculated with ZINDO. A quantum chemistry calculation software “Gaussian16” is used for the calculation. These processes correspond to the step S 1010  (input step) in the flowchart of  FIG. 3 . 
     &lt;Candidate Structure Acquisition Step&gt; 
     The above-described initial structure is randomly changed (Step S 1020 : candidate structure acquisition step). As a method of change in structure, a method in which an atom or an atomic group is added to or deleted from the chemical structure to generate an objective structure, and the objective structure is defined as the candidate structure can be used as in the first embodiment. For example, it is assumed that the first structure changes from  FIG. 4B  to  FIG. 4C . 
     &lt;Physical Property Value Calculation Step&gt; 
     In this case, as shown in  FIG. 4D , the result of estimating the physical property value of the changed structure is assumed that λmax=200 (nm) (Step S 1030 : physical property value calculation step). 
     &lt;Candidate Structure Adoption Step: First Adoption Process&gt; 
     It is determined whether or not the physical property value approaches the target value (Step S 1040 : first adoption process). Since, from |F−f1|=|367−200|=167 (nm) and |F−f0|=|367−207|=160 (nm), |F−f1|&gt;|F−f0| (the absolute value of the first difference is more than the absolute value of the second difference and the physical property value moves away from the target value), the determination in the step S 1040  is denied and the process proceeds to the step S 1050  (calculation of the probability p1). From the physical property value and the target value, the probability p1 (first probability) is calculated by the above-described first function (monotonically decreasing function P1(d) with respect to a third difference d). Here, the probability p1 is calculated by Expression (8) with σ=10 (nm). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           p 
                           1 
                         
                         = 
                         
                           
                             
                               P 
                               1 
                             
                              
                             
                               ( 
                               d 
                               ) 
                             
                           
                           = 
                           
                             
                               P 
                               1 
                             
                              
                             
                               ( 
                               
                                 167 
                                 - 
                                 160 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             exp 
                              
                             
                               [ 
                               
                                 - 
                                 
                                   7 
                                   10 
                                 
                               
                               ] 
                             
                           
                           ≅ 
                           0.50 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     Therefore, the possibility of adopting the first change in structure is almost 50%. However, it is assumed that a result of evaluation by generating a random number is “not adopt the change in structure”. In this case, the process proceeds to the step S 1060  (calculation of the probability p2; second adoption process). 
     &lt;Candidate Structure Adoption Step: Second Adoption Process&gt; 
     In the step S 1060 , the increase or decrease amount in the structural diversity is calculated, and the probability p2 (second adoption probability) is calculated by the above-described second function. As shown in  FIG. 5 , the initial structural group is defined as S0, and the structural group considering the first change in structure is defined as S1. 
     First, fingerprint is calculated. Here, the extended fingerprint is estimated using a library rcdk of R (open source programming language and development environment thereof). The length of the bit stream is 1024. The results are shown in  FIG. 6 . The numbers in the figures are bit numbers in which the value is 1. Therefore, in a case where the structure s before the change and the structure s′ after the change are as shown in  FIG. 7 , the Tanimoto coefficient and the dissimilarity of the structures are obtained by Expressions (9), (10), and (11). 
     
       
         
           
             
               
                 
                   
                     
                       
                          
                         
                           F 
                           s 
                         
                          
                       
                       = 
                       15 
                     
                     , 
                     
                       
                          
                         
                           F 
                           
                             s 
                             ′ 
                           
                         
                          
                       
                       = 
                       8 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                          
                         
                           
                             F 
                             s 
                           
                           ⋂ 
                           
                             F 
                             s 
                           
                         
                          
                       
                       = 
                       15 
                     
                     , 
                     
                       
                          
                         
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                           ⋂ 
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                         
                          
                       
                       = 
                       8 
                     
                     , 
                     
                       
                          
                         
                           
                             F 
                             s 
                           
                           ⋂ 
                           
                             F 
                             
                               s 
                               ′ 
                             
                           
                         
                          
                       
                       = 
                       8 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       T 
                       
                         s 
                         , 
                         s 
                       
                     
                     = 
                     1 
                   
                   , 
                   
                     
                       T 
                       
                         
                           s 
                           ′ 
                         
                         , 
                         
                           s 
                           ′ 
                         
                       
                     
                     = 
                     1 
                   
                   , 
                   
                     
                       T 
                       
                         s 
                         , 
                         
                           s 
                           ′ 
                         
                       
                     
                     = 
                     
                       
                         8 
                         
                           15 
                           + 
                           8 
                           - 
                           8 
                         
                       
                       ≅ 
                       0.53 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       v 
                       
                         s 
                         , 
                         s 
                       
                     
                     = 
                     0 
                   
                   , 
                   
                     
                       v 
                       
                         
                           s 
                           ′ 
                         
                         , 
                         
                           s 
                           ′ 
                         
                       
                     
                     = 
                     0 
                   
                   , 
                   
                     
                       v 
                       
                         s 
                         , 
                         
                           s 
                           ′ 
                         
                       
                     
                     = 
                     
                       
                         1 
                         - 
                         
                           T 
                           
                             s 
                             , 
                             
                               s 
                               ′ 
                             
                           
                         
                       
                       ≅ 
                       0.47 
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     Therefore, the dissimilarity of the structural group is obtained by Expression (12). 
     
       
         
           
             
               
                 
                   
                     
                       V 
                        
                       
                         ( 
                         
                           S 
                           0 
                         
                         ) 
                       
                     
                     = 
                     0 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         
                           
                             V 
                              
                             
                               ( 
                               
                                 S 
                                 1 
                               
                               ) 
                             
                           
                            
                             
                           = 
                           
                             
                               
                                 2 
                                 
                                   25 
                                    
                                   
                                     ( 
                                     
                                       25 
                                       - 
                                       1 
                                     
                                     ) 
                                   
                                 
                               
                                
                               
                                 
                                   ∑ 
                                   
                                     j 
                                     = 
                                     2 
                                   
                                   25 
                                 
                                  
                                 
                                     
                                 
                                  
                                 
                                   v 
                                   
                                     
                                       s 
                                       11 
                                     
                                     , 
                                     
                                       s 
                                       
                                         1 
                                          
                                         j 
                                       
                                     
                                   
                                   2 
                                 
                               
                             
                             = 
                             
                               
                                 1 
                                 300 
                               
                               × 
                               
                                 0.47 
                                 2 
                               
                               × 
                               24 
                             
                           
                         
                       
                     
                     
                       
                         
                             
                            
                           
                             ≅ 
                             0.017 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     Therefore, in a case of obtaining the increase or decrease amount dv in the structural diversity (structural diversity is evaluated by the above-described “evaluation method of structural diversity (1)”), the increase or decrease amount dv=V(S1)−V(S0)≈0.017&gt;0. That is, since the diversity is improved by the change in structure, the process proceeds to the calculation of the probability p2 (second adoption probability) (Step S 1060 : second adoption process). Assuming that σv=0.01 and Cv=0.5 in Expression (7), the probability p2 can be calculated as in Expression (13). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           p 
                           2 
                         
                          
                           
                         = 
                         
                           
                             
                               P 
                               2 
                             
                              
                             
                               ( 
                               
                                 d 
                                 v 
                               
                               ) 
                             
                           
                           = 
                           
                             0.5 
                             × 
                             
                               ( 
                               
                                 1 
                                 - 
                                 
                                   exp 
                                   ( 
                                   
                                     
                                       - 
                                       0.017 
                                     
                                      
                                     
                                       / 
                                     
                                      
                                     0.01 
                                   
                                   ] 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           ≅ 
                           0.41 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     In a case where the change in structure is adopted as a result of evaluation by generating a random number in the step S 1060 , the process proceeds to the step S 1070 . Then, the first change in structure is formally adopted and benzene is registered as a new structure (refer to  FIG. 8 ). The same process is performed for the other 24 structures. 
     On the other hand, in a case where the change in structure is not adopted in the step S 1060 , the process proceeds to the step S 1080 , and as shown in  FIG. 9 , the structure is returned to the structure before the change in structure (rejecting the change in structure; rejection process). 
     It is assumed that the structural group shown in  FIG. 10  is obtained as a result of evaluating all 25 structures. The reason why the phenol of the initial structure remains as it is in the structural group of  FIG. 10  is that the change in structure is rejected in the step S 1060  (adopting the change in structure with the probability p2) and the process proceeds to the step S 1080 . Even in a structure among the structures shown in  FIG. 10 , which has a physical property value closest to the target value, λmax=208 (nm) (refers to  FIG. 11 ), which does not reach the target value of 367 nm. Therefore, the determination in the step S 1090  is denied, and the process returns to the step S 1020  (control step). 
       FIG. 12  shows how the structure and λmax change in a case of repeating the above-described process. In the structure appearing in the 113th trial, λmax matches the target, and it is confirmed that a compound having a target physical property can be acquired by solving the inverse problem in the present invention. The structure appearing in the 113th trial is a real compound called methyl yellow. Since the physical property value has reached the target, the process may be terminated here, but it is assumed that the search is continued here. Then, in a case where the upper limit of the number of trials is set to 500, the process is terminated in a case where the number of trials reaches the upper limit of 500 (that is, where the termination condition is satisfied here) (in a case of Yes in the step S 1090 , the process proceeds to the step S 1100 ; control step). By 500 trials, in addition to the above-described methyl yellow, many compound structures expected to have the desired λmax can be acquired (for example, structures shown  FIGS. 13A and 13B ). 
     &lt;Comparison with Other Methods&gt; 
     Bayesian inference is usually used as another method. Here, the results calculated using a particulate filter which is a type of Bayesian inference are compared with the results obtained in the present invention. The search for a compound having λmax=367 (nm) is performed using a particulate filter under the same λmax calculation condition as in the above-described example. The λmax of top 50 compounds among the compounds obtained up to 500th trial is shown together with the results of the present invention (refer to  FIG. 14 ). In the Bayesian inference, only a few compounds having λmax equivalent to the target value is obtained, but in the present invention, all the top 50 compounds have λmax equivalent to the target value. Therefore, it can be said that “the present invention is able to search the structure more efficiently than the Bayesian inference”. 
     In order to clarify the reason for the low search efficiency in the Bayesian inference, the average value of λmax of the top 50 compounds with respect to the number of trials was plotted (refer to  FIGS. 15A and 15B ). As a result, it is found that, in the Bayesian inference, the search falls into the local minimum twice. On the other hand, in the present invention, the search can be performed smoothly without falling into the local minimum. Furthermore, as a result of examining the structural diversity (value of V(S) described above) of the top 50 compounds in the 500th trial, the diversity of the present invention is larger than that of the Bayesian inference (refer to  FIG. 16 ). This means that “a group which is structurally more diverse while having the same physical property value as the target value is acquired”. 
     As described above, according to the present invention, the search efficiency is significantly improved compared to the Bayesian inference method commonly used. In addition, the structural diversity of the obtained compound also increases. 
     &lt;Relationship Between Evaluation Method of Structural Diversity and Efficiency of Structural Search&gt; 
     In the above-described example, the structural diversity is evaluated by the “evaluation method of structural diversity (1)”, but the structural search can be performed with the same efficiency in a case of using the “evaluation method of structural diversity (2)”. Specifically, as a result of calculating a mean square error with the target λmax (367 nm) of top 20 compounds (1st, 2nd, . . . in order of physical property value closer to the target value) in each trial, as shown in  FIG. 17 , in either case of the “evaluation method of structural diversity (1)” and the “evaluation method of structural diversity (2)”, “mean square error&lt;100 (nm 2 )” can be achieved after approximately 20 trials. In the “evaluation method of structural diversity (2)”, Sprev is set to “top 100 structures having physical property values close to the target value, among structures generated in the past trials”. 
     Other Examples 
       FIG. 18  shows structural search results in a case of including methyl yellow (one example of the above-described “compounds from existing library”) in a comparative target of the diversity. As a result of the structural search, methyl yellow is not generated, and many candidate compounds having low similarity to methyl yellow (having small Tanimoto coefficient) can be obtained. The numerical values in  FIG. 18  are values in the 500th trial. In addition, as described above, the Tanimoto coefficient is one of indexes showing similarity of structures of compounds, and takes a value of 0 to 1 (similarity is higher as the value is closer to 1). 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described. In the above-described first embodiment, the first adoption process is performed first, and in a case where the candidate structure is not adopted by the first adoption process, the second adoption process is performed. However, in the second embodiment, the second adoption process is first performed contrary to the first embodiment, and in a case where the candidate structure is not adopted by the second adoption process, the first adoption process is performed. 
     In the second embodiment, the configuration of the device for searching a compound  10  (device for searching a compound) can adopt the configuration shown in  FIGS. 1 and 2  as in the first embodiment. 
       FIG. 19  is a flowchart showing a process of the method for searching a compound and program for searching a compound according to the second embodiment. In  FIG. 19 , the same step number is assigned to a step which performs the same process as in  FIG. 3 , and detailed description thereof will be omitted. In addition, a non-temporary and computer-readable recording medium, which causes a computer to execute the program according to the flowchart of  FIG. 19  in a case where a command stored in the recording medium is read by the computer, is also an aspect of the second embodiment. 
     In a case where the candidate structure adoption part  108  (candidate structure adoption part) determines No (the physical property value does not approach the target value) in the step S 1040 , the process proceeds to a step S 1052 . The detail of the step S 1052  (second adoption process) is the same as that of the step S 1055  in  FIG. 3 , and the candidate structure adoption part  108  can evaluate the structural diversity by the above-described “evaluation method of structural diversity (1)” or the above-described “evaluation method of structural diversity (2)”. 
     In a case where the determination is affirmed in the step S 1052 , the process proceeds to a step S 1057 , and the candidate structure adoption part  108  calculates the probability p2 (second adoption probability) by the monotonically increasing function P2(dv) in the same manner as in the step S 1060  of  FIG. 3  (second adoption process). After obtaining the probability p2, the candidate structure adoption part  108  uses an appropriately generated random number to adopt the change in structure with the probability p2 (Step S 1070 : second adoption process). In a case where the change in structure is not adopted in the step S 1057 , the process proceeds to a step S 1062 . 
     In the step S 1062 , the candidate structure adoption part  108  calculates the probability p1 (first adoption probability) from the physical property value and the target value in the same manner as in the step S 1050  (first adoption process), and uses an appropriately generated random number to adopt the change in structure with the probability p1 (Step S 1070 : first adoption process). In a case where the change in structure is rejected, the process proceeds to the step S 1080 , and the candidate structure adoption part  108  rejects the change in structure and returns to the original structure (rejection process). In the step S 1052 , even in a case where the determination is denied (a case where the structural diversity does not increase), rather than immediately rejecting the change in structure, the candidate structure adoption part  108  leaves room for adoption based on the physical property value and the target value (proceeding to the step S 1062 ). 
     Even in the case of the second embodiment described above, as the first embodiment, it is possible to efficiently search for the structure of the compound having a desired physical property value. 
     The adoption probability according to the flowchart of  FIG. 19  is equivalent to that of  FIG. 3 . The adoption probability of the change in structure, in a case of being evaluated in the order of “physical property→structural diversity” as shown in  FIG. 3 , is “p1+(1−p1)×p2=p1+p2−p1×p2”, but the adoption probability of the change in structure, in a case of being evaluated in an order of “structural diversity→physical property” as shown in  FIG. 19 , is “p2+(1−p2)×p1=p1+p2−p1×p2”. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described. In the above-described first and second embodiments, in a case where one of the first and second adoption processes is performed and the candidate structure is not adopted, the other adoption process is performed, but in the third embodiment, the first and second adoption processes are performed simultaneously. 
     In the third embodiment, the configuration of the device for searching a compound  10  (device for searching a compound) can adopt the configuration shown in  FIGS. 1 and 2  as in the first embodiment. 
       FIG. 20  is a flowchart showing a process of the method for searching a compound and program for searching a compound according to the third embodiment. In  FIG. 20 , the same step number is assigned to a step which performs the same process as in  FIG. 3 , and detailed description thereof will be omitted. In addition, a non-temporary and computer-readable recording medium, which causes a computer to execute the program according to the flowchart of  FIG. 20  in a case where a command stored in the recording medium is read by the computer, is also an aspect of the third embodiment. 
     In a case where the candidate structure adoption part  108  (candidate structure adoption part) determines No (the physical property value does not approach the target value) in the step S 1040 , the process proceeds to a step S 1054 . In the step S 1054 , the candidate structure adoption part  108  calculates the probability p1 (first adoption probability) in the same manner as in the steps S 1050  and S 1062  described above (first calculation process). 
     In addition, in a case where the candidate structure adoption part  108  (candidate structure adoption part) determines No in the step S 1040 , the process proceeds to a step S 1059 . In the step S 1059 , the candidate structure adoption part  108  can determine whether or not the structural diversity increases by the “evaluation method of structural diversity (1)” or the “evaluation method of structural diversity (2)” as in the steps S 1055  and S 1052 . On the other hand, in a case where the determination is affirmed in the step S 1059 , the process proceeds to a step S 1064 , the candidate structure adoption part  108  calculates the probability p2 (second adoption probability) in the same manner as in the steps S 1060  and S 1057  described above (second calculation process), and the process proceeds to a step S 1065 . The first calculation process and the second calculation process may be performed concurrently, or one of these may be performed first. However, whether to or not to adopt the candidate structure is determined after the probability p1 and the probability p2 are calculated. 
     In the step S 1065 , the candidate structure adoption part  108  decide whether to or not to adopt the candidate structure based on the probability p1 (first adoption probability) and the probability p2 (second adoption probability) (adoption process). For example, the candidate structure adoption part  108  can adopt the candidate structure with a “larger probability of the probabilities p1 and p2”. In addition, the candidate structure may be adopted with a “smaller probability of the probabilities p1 and p2”, an “average probability of the probabilities p1 and p2”, a “simultaneous probability (=p1 x p2) of the probabilities p1 and p2”, or the like. The candidate structure adoption part  108  proceeds to the step S 1070  with such a probability (adoption probability) and adopts the candidate structure (adoption process), and proceeds to the step S 1080  with (1−adoption probability) and rejects the change in structure and returns to the original structure (rejection process). 
     In the step S 1059 , even in a case where the determination is denied (a case where the structural diversity does not increase), rather than immediately rejecting the change in structure, the candidate structure adoption part  108  leaves room for adoption of the change in structure (sets the probability p2 to 0 and proceeds to the step S 1065 ). 
     Even in the case of the third embodiment described above, as the first and second embodiments, it is possible to efficiently search for the structure of the compound having a desired physical property value. 
     The embodiments and examples of the present invention have been described above, but the present invention is not limited to the above-described aspects, and various modifications are possible without departing from the gist of the present invention. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               10 : device for searching compound 
               100 : processing part 
               102 : input part 
               104 : candidate structure acquisition part 
               106 : physical property value calculation part 
               108 : candidate structure adoption part 
               110 : control part 
               112 : display control part 
               120 : CPU 
               122 : ROM 
               124 : RAM 
               200 : storage part 
               300 : display part 
               310 : monitor 
               400 : operation part 
               410 : keyboard 
               420 : mouse 
               500 : external server 
               510 : external database 
               1000 : network 
             S 1010  to S 1100 : each step of method for searching compound