bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonadiabatic NO expansions for the ground state wave function of H
Authors: Blanke Gerd , Kleindienst Heinz 
Published: January 2005

AbstractIn this article, direct calculations of nonadiabatic NO expansions for the ground‐state wave function of H are given, as predicted by Bishop and Cheung. Two methods are presented, i.e., an analogon to the Ahlrichs/Driessler procedure and a gradient method, both originally developed to calculate natural orbitals for two‐electron systems. © 1994 John Wiley & Sons, Inc.
Frequency‐dependent hyperpolarizabilities in the brueckner coupled‐cluster theory
Authors: Aiga Fumihiko , Sasagane Kotoku , Itoh Reikichi 
Published: January 2005

AbstractA formulation for calculating frequency‐dependent hyperpolarizabilities in the coupled‐cluster (CC) theory with the Brueckner orbitals is presented. Our quasi‐energy derivative (QED) method is applied, and explicit expressions for response properties up to third order [μ, α(−ω1;ω1), β(−ωσ;ω1, ω2)] are derived. The position of the resonances is determined from the RPA‐like equation. It is found that the pole structures are not compatible with ones of the exact response functions. An extension of the coupled Brillouin–Brueckner CEPA‐0 by Kutzelnigg to the time‐dependent case is also discussed. © 1994 John Wiley & Sons, Inc.
Activation hardness and cycloadditions of even linear polyenes
Authors: Ray N. K. , Rastogi R. C. 
Published: January 2005

AbstractModes of thermal and photochemical cycloaddition of even linear polyenes are examined using the simple concept of activation hardness. The results are in agreement with the well‐known Woodward–Hoffman rules. [R.B. Woodward and R. Hoffmann, The Conservation of Orbital Symmetry (Academic Press, New York, 1989)]. © 1994 John Wiley & Sons, Inc.
Self‐dual phase‐space representation of quantum mechanics and the variational principle
Authors: Włodarz Joachim J. 
Published: January 2005

AbstractThe important duality problem of phase‐space representations of quantum mechanics is discussed and the class of self‐dual representations is established. It is shown that self‐dual phase‐space representations may be endowed with a Hilbert space structure resembling the standard picture of quantum mechanics. A stationary variational principle is then formulated, enabling one to solve eigenproblems of observables directly in phase space. A modified, more usable form of this variational principle is also given together with an example of practical application to the 1D Coulomb system. © 1994 John Wiley & Sons, Inc.
Dimer form of 1,3‐dimethyluracil studied by the AM1 semiempirical method
Authors: Palafox M. Alcolea , Iza N. , Gil M. 
Published: January 2005

AbstractA study of the dimer form of 1,3‐dimethyluracil was carried out. The optimum geometric parameters in the monomeric and dimeric forms were obtained using the AM1 semiempirical method. The results were compared with those reported by X‐ray diffraction. The energies in the dimer formation and in the intramolecular CH···O interaction were calculated. Electronic density maps in two and three dimensions were drawn. Several calculated thermodynamic parameters are discussed. © 1994 John Wiley & Sons, Inc.
Modified valence indices from the two‐particle density matrix
Authors: Nalewajski Roman F. , Mrozek Janusz 
Published: January 2005

AbstractThe modified ionic and covalent valence indices are introduced, defined in the framework of the two‐particle density matrix, with respect to the reference state of separated atoms or ions (SAL). They include only quadratic contributions in changes of the molecular charge‐and‐bond order matrix elements, relative to the SAL. General properties of the modified valence indices are examined and illustrative qualitative results for model systems are presented. Numerical UHF SCF MO valence data for selected diatomic and triatomic molecules are reported and interpreted in terms of the valence saturation effect and the ionic vs. covalent valence competition. A three‐orbital valence model of a symmetric transition state of the bond‐forming–bond‐breaking reaction supports the BEBO model postulate of preservation of the total “bond order.” The model predictions are compared with the UHF numerical values. © 1994 John Wiley & Sons, Inc.
On exact calculation of response properties of oscillators in static electric field: A Fourier grid Hamiltonian approach. I. One‐dimensional systems
Authors: Dutta P. , Bhattacharyya S. P. 
Published: January 2005

AbstractThe Fourier grid Hamiltonian method is used to calculate the response properties of different types of 1‐d (one‐dimensional) quantum oscillators in a uniform static electric field. The calculations are potentially exact. Excepting the harmonic oscillator, the other model oscillators studied are seen to possess nonlinear polarizabilities. In general, the polarizabilities are not monotonic functions of appropriate vibrational quantum numbers. The exact nature of this vibrational‐state dependence of polarizabilities is shown to depend on the type of mechanical anharmonicity in which the nuclei move and the nature of electrical anharmonicity characterizing the field–oscillator coupling. The large vibrational contribution to nonlinear polarizabilities often predicted for real diatomics could therefore originate from the mechanical and electrical anharmonicities of the potential in which the nuclei move when placed in a static electric field. © 1994 John Wiley & Sons, Inc.
Character of the electronic ground state and of charge‐transfer excited states in ionic solids: An ab initio cluster model approach
Authors: Casanovas Jordi , Lorda Amparo , Sousa Carmen , Illas Francesc 
Published: January 2005

AbstractThe electronic structure of the ground electronic state and of some special charge‐transfer excited states in ionic solids is examined from the ab initio cluster model approach. Different ab initio wave functions, including a frozen orbital approach, the Hartree–Fock self‐consistent field, and multireference configuration interaction wave functions, are considered and analyzed using different theoretical techniques. We explicitly consider some alkaline–earth oxides such as CaO, a more difficult case such as A12O3, a transition‐metal oxide such as NiO, and a system with a more complicated structure such as KNiF3. Analysis of ab initio wave functions in terms of valence bond components shows that all these compounds are largely ionic, thus supporting the simple picture arising from the ionic model. However, the nature of the excited states is more complex. Alkaline–earth oxides lowest excited states are essentially described as charge‐transfer excitations dominated by a single resonant valence bond structure and the calculated energy difference is comparable to the experimental optical gap. In the case of A12O3, the electronic spectra presents excitonic features and the local charge‐transfer excitation excited states provide a reasonable representation of these phenomena. Finally, several different valence bond structures are present in the lowest electronic states of KNiF3. © 1994 John Wiley & Sons, Inc.
Quantum chemical calculation of nickel and copper atomic valencies in crystalline oxides
Authors: Evarestov R. A. , Tupitsin I. I. , Veryazov V. A. 
Published: January 2005

AbstractA new quantum chemical definition is proposed of the full atomic valence, VA, taking into account both the covalent and ionic parts of the chemical bonds formed by atoms in molecules and crystals. The full atomic valencies, covalencies, and charges on atoms are calculated for nickel–oxygen crystalline compounds in the CNDO band theory approximation. A comparison of the chemical bonding in nickel and copper crystalline oxides is given. © 1994 John Wiley & Sons, Inc.
Statistical mechanical theory of liquid entropy
Authors: Wallace Duane C. 
Published: January 2005

AbstractThe multiparticle correlation expansion for the entropy of a classical monatomic liquid is presented. This entropy expresses the physical picture in which there is no free particle motion, but, rather, each atom moves within a cage formed by its neighbors. The liquid expansion, including only pair correlations, gives an excellent account of the experimental entropy of most liquid metals, of liquid argon, and of the hard‐sphere liquid. The pair correlation entropy is well approximated by a universal function of temperature. Higher‐order correlation entropy, due to n‐particle irreducible correlations for n ≥ 3, is significant in only a few liquid metals, and its occurrence suggests the presence of n‐body forces. When the liquid theory is applied to the study of melting, we discover the important classification of normal and anomalous melting, according to whether there is not or is a significant change in the electronic structure upon melting, and we discover the universal disordering entropy for melting of a monatomic crystal. Interesting directions for future research are extension to include orientational correlations of molecules, theoretical calculation of the entropy of water, application to the entropy of the amorphous state, and correlational entropy of compressed argon. We clarify the relation among different entropy expansions in the recent literature. © 1994 John Wiley & Sons, Inc.
The character of the correlations in DNA sequences
Authors: Borštnik B. 
Published: January 2005

AbstractAlthough several authors proposed the existence of long‐range correlations in DNA sequences [W. Li and K. Kaneko, Europhys. Lett. 17, 655 (1992); R.F. Voss, Phys. Rev. Lett. 68, 3805 (1992); C.‐K. Peng et al., Nature 356, 168 (1992)], we claim that the real character of the correlations remains uncertain. To corroborate long‐range correlations, one should prove that the correlation functions decay as an inverse power of the distance between the nucleotides in the DNA sequence. Instead of a direct calculation of the correlation functions, one can calculate either the Fourier transforms of the sequences or the characteristics of “DNA walk.” In our previous work we pointed out that the character of the results depends upon the way the DNA sequences are chosen. When looking for the correlations separately in introns and separately in exons, we found that the resulting correlations are short range. In this work, we discuss the numerical aspects of two computational approaches: the calculation of correlation function and the evaluation of “DNA walk” characteristics. We present the analytic results for the case of exponential correlations. © 1994 John Wiley & Sons, Inc.
Evaluation of electronic matrix elements of long‐range electron transfer in proteins by the recursive residue generation method
Authors: Mikami Yasushi 
Published: January 2005

AbstractAn efficient method for calculating electronic matrix elements for electron‐transfer reactions in biological systems is proposed. We use the tight‐binding model to describe the motion of one‐electron in an array representing the system: donor (D), acceptor (A), and all other atoms that compose the protein. The matrix elements |TDA|;2 is evaluated at the estimated electron energy. The essential part of the method lies in the evaluation of the off‐diagonal Green function 〈I|G|F〉 between the site I neighboring with the donor and the site F with the acceptor. The recursive residue generation method is used to evaluate 〈I|G|F|〉. As an application, these matrix elements in metal‐labeled myoglobin are calculated and the results are compared with those evaluated with the renormalized‐perturbation‐expansion approach. © 1994 John Wiley & Sons, Inc.
On fundamentals, logic, and the connection between the natural sciences
Authors: Löwdin Per‐Olov 
Published: January 2005

AbstractThe importance of deductive theories in the modern natural sciences built essentially on experiments is briefly discussed. The logical structure of the deductive theories, their axioms, undefined quantities, and realizations is treated in some detail. In all the natural sciences, there is a striving to explain all the various phenomena in nature in terms of a few basic principles, and this “reductionism” leads to a certain amount of unification of these sciences. The chain that goes from biology, over molecular biology, biochemistry, chemistry, and physics to the description of nature in terms of the elementary particles obeying the laws of modern quantum chemistry is reviewed. Since all the measurements of microcosmos involve an observer, who according to the Copenhagen school experiences the outside universe as a projection on his or her mind through his or her senses, some theoreticians may be inclined to reduce the natural sciences to the human mind as the fundamental (undefined) quantity. However, since the observer is a biological structure, one is also back where one started, and it is evident that one can start the reduction or unification of the natural sciences in any point on this circle (or spiral). Hence, there are many descriptions of the natural sciences and their connections that are possible—as illustrated at this symposium. © 1995 John Wiley & Sons, Inc.
Applicability of quasi‐degenerate many‐body perturbation theory to quasi‐degenerate electronic states: The H4 model revisited
Authors: Mášsik Jozef , Hubačc Ivan , Mach Pavel 
Published: January 2005

AbstractThe performance of the quasi‐degenerate many‐body perturbation theory up to the third order is investigated for the ground state, five excited states, and the first quintet of a simple four‐electron H4 model system consisting of two stretched hydrogen molecules, in which the degree of quasi‐degeneracy can be continuously varied from a nondegenerate to a full degenerate situation. We employ a DZP basis set. The effect of intruder states is considered and a comparison with other multireference correlation techniques is also provided. Finally, a criterion for the model space to be quasi‐degenerate will be reformulated and generalized. © 1995 John Wiley & Sons, Inc.
Cubic‐grid Gaussian basis sets for electron scattering calculations. II. Matrix elements
Authors: Čársky Petr , Hrouda Vojtěch , Michl Josef 
Published: January 2005

AbstractIn this article, we report an efficient computational procedure for electron scattering matrix elements in the previously developed cubic‐grid Gaussian basis sets. The Green function matrix elements derived for the cubic‐grid basis set are simpler and easier to calculate than are those available in the literature for conventional Gaussian basis sets. Special features of the cubic‐grid basis sets may also be exploited for a very efficient computation of Coulomb and exchange integrals. Inelastic scattering amplitudes for vibrational excitations may be efficiently calcualted in the harmonic approximation by numerical differention of the T‐matrix elements. © 1995 John Wiley & Sons, Inc.
Cubic‐grid Gaussian basis sets for electron scattering calculations. III. Effect of basis‐set translation and size on the calculated cross section
Authors: Čársky Petr , Hrouda Vojtěch , Michl Josef , Antic Dean 
Published: January 2005

AbstractPreviously developed cubic‐grid basis sets of various sizes were used for the calculation of cross sections for elastic and inelastic electron scattering by the He and Ne atoms and the H2O molecule by the T‐matrix expansion method. The aim was to test the invariance of calculated cross sections with respect to the translation of the target molecule and to examine the effect of basis‐set size on the results. We also present a simple procedure for accounting for long‐range interactions from the part of space that lies outside the volume that contains the cubic‐grid basis set. © 1995 John Wiley & Sons, Inc.
Atomic integrals in Hylleraas–CI calculations with double‐linked correlation terms
Authors: Kleindienst H. , Büsse G. , Lüchow A. 
Published: January 2005

AbstractAtomic Hylleraas‐CI calculations with linked correlation terms of the form r r are discussed. Formulas for the integration of the radial part and the arising auxiliary integrals are deduced and convergence proofs are given. © 1995 John Wiley & Sons, Inc.
On weak and strong conjugacy in the antisymmetry principle
Authors: Palting Pancracio 
Published: January 2005

AbstractThe concept of conjugate irreducible subspaces in the algebras of permutation groups is expressed in such a way that it emphasizes the existence of conjugate pathways along a chain of subgroups of permutations. The new expression is shown to be equivalent to parity conjugation and incorporates the notion of conjugate pathways in a natural and consistent manner. The example of the Aufbau chain of symmetric subgroups is used to show how the conjugacy of pathways may be useful in the symmetry adaptation of the spatial and spin parts of Fermion state functions. It is also employed to show that one may arrive at a quantitative statement that clearly expresses the conjugacy constraints placed upon a Fermion state function in order for it to satisfy the antisymmetry principle. A simple example of these conjugacy conditions is presented. © 1995 John Wiley & Sons, Inc.
A PM3 study on intrinsic decarboxylation process of methyl–ethyl‐α–pyridylacetic acid
Authors: Nakajima Yasushi , Sakagishi Yoshikatsu , Shiibashi Michio , Suzuki Yuuji , Kato Hitoshi 
Published: January 2005

AbstractTo probe the decarboxylation process of methyl–ethyl–α pyridylacetic acid (MEPA), molecular orbital calculations on the optimized geometry, transition‐state geometry, and intrinsic reaction coordinate were performed by the MNDO–PM3 method. The salient features of the optimized structure of MEPA are that the carboxyl anion is nearly on the plane of the pyridine ring (the dihedral angle of C8C7C2N1 is 14.7°) and that the interatomic distance…︁ is used for a noncovalent bond, such as N+ 1 …︁ O−9.
of O−9 …︁ H1′ is 1.6 Å (exchange of electrons exists between their atoms). The transition‐state geometry of the decarboxylation process has the following features: (1) the activation enthalpy is 6.0 kcal/mol, (2) the dihedral angle of C8C7C2N1 is −50.2°, and (3) the interatomic distance of O−9H1′ and C7C8 increase by 111 and 124%, respectively, as compared with the optimized geometry. From the extreme beginning of the intrinsic decarboxylation process, the exchange of electrons between O−9 …︁ H1′ begins to decrease. This decrease, which is considered to be induced by the rotation of C2C7, seems to initiate the dissociation of C7C8. © 1995 John Wiley & Sons, Inc.
Large basis sets and geometry optimizations in embedded cluster calculations
Authors: Teunissen E. H. , Jansen A. P. J. 
Published: January 2005

AbstractIn the embedded cluster method, a cluster is embedded in a correction potential. This potential adds the long‐range electrostatic forces of the crystal and subtracts the electrostatic potential of the boundary errors of the cluster. The correction potential is calculated from the wave function of the cluster and the crystal. So far, the method has only been used on a cluster having the same geometry and basis set as that of the crystal. Here, we calculated the adsorption energies of NH3 and NH4+ on an embedded zeolite cluster with different basis sets and modified geometries. We showed that a mixed basis set, a basis set having a large basis set on the atoms around the adsorption site and a minimal basis set on the atoms of the boundary of the cluster, yields adsorption energies close to that of the large basis set. The optimized geometries of the zeolite acidic site were almost equal for the nonembedded cluster, the embedded cluster, and the crystal. By combining the mixed basis set with a partial geometry optimization, an improved description of the adsorption process is obtained. © 1995 John Wiley & Sons, Inc.
A quantum chemical study of small beryllium hydrides and their radical anions
Authors: Polášek M. , Zahradník R. 
Published: January 2005

AbstractMolecular structures of neutral and anionic beryllium hydrides have been investigated using ab initio calculations at the MP2 (geometries) and MP4 (energies)/6 – 31++G** levels. ZPE and (if possible) BSSE correction have been included. While BeH2− is not stable, the radical anion of the beryllium hydride dimer is significantly stabilized with respect to the neutral Be2H4 system. Moreover, this anion can appear in two isomeric forms with comparable stability. © 1995 John Wiley & Sons, Inc.
Über das Verhalten der Bleisalze in Lösungen
Authors: Von Ende Carl L. 
Published: January 2005

AbstractAls Hauptergebnis dieser Untersuchung wäre anzuführen, die Feststellung der stufenweisen Dissoziation. Die Dissoziation des Bleichlorids folgt nicht dem Schema PbCl2  Pb‥ + 2 Cl′, sondern dem Schema

und zwar ist die der ersten Stufe stärker als die der zweiten, es herrscht ein gewisses Widerstreben gegen die Aufnahme einer zweiten Ladung. Ohne diese stufenweise Dissoziation lässt sich das tiefe Löslichkeitsminimum nicht erklären, denn alle Bestimmungen des Grades der Dissoziation unter Vernachlässigung derselben ergeben Werte für die undissoziierte Menge, die weit grösser als die kleinste Löslichkeit.
Über tetragene Doppelsalze mit besonderer Berücksichtigung des Kainits
Authors: Meyerhoffer W. 
Published: January 2005

Abstract1. Ein tetragenes, d. h. ein abgesehen von Kristallwasser aus vier verschiedenen Radikalen (Ionen) zusammengesetztes Salz besitzt zwei oder drei Bildungstemperaturen. Die beiden des Kainits MgSO4.KCl.3H2O liegen bei etwa 76° und 85°.
Über die Schmelzpunkte der Mischungen der alkalischen Erden mit Borsäureanhydrid
Authors: Guertler W. 
Published: January 2005

AbstractZusammenfassungIn nebenstehender Figur 6 sind die Schmelzkurven der drei Erdalkalioxyde mit Borsäureanhydrid zusammengestellt und gleichzeitig die durch frühere Versuche festgestellten Konzentrationen eingetragen, welche bei 0 bis 1400° an Borsäureanhydrid gesättigt sind.1 Diesen drei Konzentrationen entsprechen kurze vertikale Striche, welche die zugehörigen Schmelzkurven abschliessen.
Beiträge zur Kenntnis der Polysulfide. II
Authors: Küster F. W. 
Published: January 2005

AbstractZum Schluss sollen die Resultate vorstehender Arbeit hier noch einmal kurz zusammengefasst werden:
Der Auflösungsvorgang von Schwefel in Natriumsulfid kann durch Potentialmessung bis zur Sättigung messend verfolgt werden.
Zwischen dem Potential von Platinelektroden in mit Schwefel gesättigten Natriumpolysulfidlösungen und der Verdünnung dieser Lösungen bestehen einfache Beziehungen, die durch die NERNSTSche Formel ihren zutreffenden Ausdruck finden.
Dasselbe gilt für angreifbare Silberelektroden.
Zur Kenntnis der Zirkonschwefelsäuren
Authors: Ruer Rudolf , Levin Max 
Published: January 2005

AbstractAusser dem neutralen Zirkonsulfat, welches, wie a. a. O. gezeigt wurde, in wässeriger Lösung eine komplexe Konstitution besitzt und als eine Zirkonschwefelsäure aufzufassen ist, gibt es noch eine oder wahrscheinlich eine Reihe von Zirkonschwefelsäuren, welche, bezogen auf die gleiche Menge Schwefelsäure, mehr Zirkonoxyd enthalten, als das neutrale Zirkonsulfat. Auch hier bildet bei der elektrolytischen Dissoziation das Zirkon zusammen mit den Sulfatgruppen ein komplexes Anion. Eine Lösung, welche im wesentlichen diese zirkonreicheren Zirkonschwefelsäuren enthält, wird erhalten durch Auflösen von Zirkonhydroxyd in einer Lösung von neutralem Zirkonsulfat unter Erwärmen auf dem Wasserbade.
Über Atomgewichtsbestimmung von seltenen Erden
Authors: Brill Otto 
Published: January 2005

Abstract1. Es wurde gezeigt, dass die KRÜSSsche Temperaturangabe für die Bildung des normalen Sulfats unrichtig ist und dass man die sauren Sulfate bei ca 480° erhitzen muss, um rasch Gewichtskonstanz zu erhalten. Bei dieser Temperatur tritt unter normalen Verhältnissen noch keine weitere Zersetzung ein.
Die Chromate von Quecksilber, Wismut und Blei
Authors: Cox Alvin J. 
Published: January 2005

Abstract1. Durch Untersuchung vom Standpunkt der Phasenregel ist es möglich, die existierenden Salzindividuen von Gemischen zweier Salze in verschiedenen Verhältnissen, die in die chemische Literatur als Verbindungen übergegangen sind, zu unterscheiden.