bluuebunny/crossref_metadata_2025_split huggingface dataset:
Static polarizabilities for the ne‐isoelectronic series using Harbola–Sahni potential
Authors: Samuel J. , Sen K. D. 
Published: January 2005

AbstractThe recently proposed Harbola–Sahni local potential in its exchange‐only version [Phys. Rev. Lett. 62, 689 (1989)] is found to give the static dipole and quadrupole polarizabilities for the Neisoelectronic series in excellent agreement with the corresponding Hartree–Fock estimates. © 1992 John Wiley & Sons, Inc.
Atomic theorems
Authors: Bader R. F. W. , Popelier P. L. A. 
Published: January 2005

AbstractThe atomic statement of the principle of stationary action determines the theorems that establish the mechanics of an atom in a molecule. The atomic torque, power, and current theorems are derived. They, along with the atomic force, virial, and continuity theorems, provide a complete description of the behavior of matter at the atomic level, including the effects of electric and magnetic fields. The atomic power theorem, for example, enables one to determine the atomic or molecular source of the creation and dissipation of power in combustion or in an explosion. An atom in a molecule is an open system and an atomic equation of motion for an observable contains a component corresponding to the flux in its current density through the atomic surface. The differential form of each theorem yields an equation of motion for the corresponding property density in which the same surface flux appears as a divergence of the current density. The differential and integrated atomic theorems complement those for the total system, enabling one to relate the property to its atomic components and ultimately to a local contribution from each element in real space. © 1993 John Wiley & Sons, Inc.
Classical and quantum study of a generalized Kepler–Coulomb system
Authors: Kibler Maurice , Campigotto Corrado 
Published: January 2005

AbstractThe nonrelativistic potential V = α/r + β cos θ/(r sin θ)2 + γ/(r sin θ)2, which constitutes an extension of the Kepler‐Coulomb potential and of the Hartmann potential, is investigated from both a classical and a quantum mechanical viewpoint. The corresponding Schrödinger equation is solved in parabolic coordinates by using the Kustaanheimo‐Stiefel transformation. The accidental degeneracy for the discrete spectrum is explained through the introduction of an su(2) dynamical invariance algebra. The Hamilton–Jacobi equation is solved in parabolic coordinates. The planarity and the periodicity of the trajectories are investigated. All finite trajectories are found to be quasi‐periodic (rather than periodic as in the case of the Kepler–Coulomb system). © 1993 John Wiley & Sons, Inc.
Dipole, quadrupole, octupole, and dipole–octupole polarizabilities at real and imaginary frequencies for H, HE, and H2 and the dispersion‐energy coefficients for interactions between them
Authors: Bishop David M. , Pipin Janusz 
Published: January 2005

AbstractWe have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H2 and the dispersion‐energy coefficients for long‐range interactions between them. We have done so in a sum‐over‐states formalism with explicitly electron‐correlated wave functions to describe the states. To be precise, we have determined the dipole (α1), quadrupole (α2), and octupole (α3) polarizabilities of H and He for real frequencies (ω) in a range between zero and the first electronic‐transition frequency and for imaginary frequencies (iω) on a 32‐point Gauss‐Legendre grid running from zero to ħω = 20 Eh, and for H2, we have found the dipole (α), quadrupole (C), and dipole–octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion‐energy coefficients, obtained by combining the sum‐over‐states for‐malism for the polarizabilities with analytic integration over ω, gave values of C6, C8, and C10 for the atom–atom systems; C, C, C, C, and C for the atom–diatom systems; and C6, C and C for the H2H2 system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iω), E(ω), and E(iω) for H2 and C, C, and C for the HH2 system. © 1993 John Wiley & Sons, Inc.
Solution of atomic and molecular Schrödinger equation described by hyperspherical coordinates
Authors: Deng Conghao , Zhang Ruiqin , Feng Dacheng 
Published: January 2005

AbstractThe Schrödinger equation for an atom or molecule is expressed in terms of hyperspherical coordinates. The eigenfunction is expanded in a series of orthonormal complete sets: Yλ,μ(Ω), eigenfunctions of generalized angular momentum scalar operator, and L, generalized Laguerre polynomials. The recurrence relation of the expansion coefficients are derived and the eigenvalues can be obtained from the secular equation. © 1993 John Wiley & Sons, Inc.
A theoretical study of the effect of basis sets on stationary structures for the addition of carbon dioxide to methylamine: A relation among geometries, energy status, and electronic structures
Authors: Andréas J. , Moliner V. , Krechl J. , Silla E. 
Published: January 2005

AbstractThe carbon dioxide (CO2) to methylamine (CH3NH2) addition reaction is investigated using an ab initio MO method with the aim of obtaining an insight into the relation between transition‐state structure and reactivity. The complete potential energy hypersurface was explored and the stationary points representing reactants, transition state, and product were localized. To establish the relevance of different basis sets, calculations were carried out at different levels of theory: STO‐3G, 3‐21G, 4‐21G, 4‐31G, 6‐31G, 6‐311G, 6‐31G*, and MP2/6‐31G*//HF/6‐31G*. A reaction analysis done by correlation of bond‐order indices using the More O'Ferrall‐Jencks diagram reveals the reaction mechanism as an asynchronous process. The transition state can be described as a four‐membered ring. The lone nitrogen electron pair of the amine appears as the driving force of the reaction, where a positive hydrogen rather than a radical is more likely to be transferred. © 1993 John Wiley & Sons, Inc.
Electron attachment to homonuclear diatomic molecules
Authors: Mosley D. H. , Pickup B. T. 
Published: January 2005

AbstractThe electron propagator method is applied to the calculation to the electron affinities of some first‐ and second‐row homonuclear diatomic molecules Li2, Be2, C2, F2, Na2, Si2, and Cl2. Perturbation theory is applied through second order to analyze the results in order to determine the relative importance of correlation and relaxation effects in the binding of the additional electron. © 1993 John Wiley & Sons, Inc.
Polysila analogs of aromatic hydrocarbon ions: Structures and energies of Si3H3+, Si4H, and Si5H5−
Authors: Korkin Anatoli , Glukhovtsev Mikhail , von Ragué Schleyer Paul 
Published: January 2005

AbstractSilicon analogs of aromatic monocyclic ions, (SiH) (4), (SiH) (5), and (SiH) (6) have been studied ab initio at MP2(full)/6‐31G*. The D3h structure of Si3H3+ is the global minimum, whereas other two ions are nonplanar. The D2d structure of (SiH) is less folded than the carbon analog and possesses a higher stabilization energy. Stabilization energies for the monocharged ions are diminished with respect to the corresponding carbons © 1993 John Wiley & Sons, Inc.
Ab initio investigation of phloroglucinol
Authors: Mandix Kim , Colding Arne , Elming Knud , Sunesen Leif , Shim Irene 
Published: January 2005

AbstractAll‐electron ab initio Hartree–Fock (RHF) calculations have been carried out to investigate the keto/enol equilibrium of phloroglucinol. The calculations predict that the enol form of phloroglucinol, 1,3,5‐benzenetriol, is by far the most stable of the two. This is confirmed by NMR spectra taken on phloroglucinol. A comparison of the keto enol form transformation of phloroglucinol with that of the phenol system shows that the keto form of phloroglucinol, 1,3,5‐cyclohexanetrion, is more abundant in the phloroglucinol system, and the keto form of phenol, 2,4‐cyclohexadien‐1‐on, in the phenol system. © 1993 John Wiley & Sons, Inc.
Resonances and irreversibility for Schrödinger evolution
Authors: Kurasov P. , Elander N. , Pavlov B. 
Published: January 2005

AbstractThe relations between the Schrödinger and wave evolutions are investigated. A generalization of the Lax‐Phillips scattering theory for the case of the Schrödinger equation is constructed. An analog of the wave decay operator is obtained. The general ideas are illustrated by an explicitly solvable model of multichannel scattering on the halfaxis. A Lax‐Phillips scattering theory is developed for the model operator obtained by a self‐adjoint perturbation of the background operator. © 1993 John Wiley & Sons, Int.
Some comments on H‐bond dynamics in DNA base pairs
Authors: Brändas Erkki J. 
Published: January 2005

AbstractIt is advocated that the H‐bond patterns of the standard C–G and A–T base pairs have an evolutionary advantage over any other H‐bond scheme accommodated within the Watson–Crick‐type geometry. A suggested proof of the statement is given by the Longuet–Higgins' sign‐reversing loop argument. The present analysis indicates a close relation with self‐organizational principles. © 1993 John Wiley & Sons, Inc.
Self‐returning walks and fractional electronic charges of atoms in molecules
Authors: Bonchev D. , Kier L. B. , Mekenyan O. 
Published: January 2005

AbstractThree hierarchically ordered topological factors, i.e., atom connectivity, centrality, and cyclicity, were found to control the number of self‐returning walks (SRWS) associated with every atom in the molecule. The reversal of their order was observed in a few cases where the central location of atoms had a stronger influence than did their connectivity on the number of SRWS. Three atomic topological indices, i.e., the Morgan extended connectivity, the Balaban, Mekenyan, and Bonchev hierarchical extended connectivity, the Randić atomic path code, were found to closely match the ordering of atoms in molecules determined by their number of SRWS. New atomic graph invariants fi = lim SRW/SRWn and ti = fi · SRW2 were specified and may find application in QSAR and QSPR. The ti indices are nonintegers close to atomic valence. The fi indices represent the limit of the number of SRWS of length n for the atom i, SRW, normalized by dividing it by the total number of SRWS for the molecule. In the case of Hückel MO considerations, these invariants were shown to be numerically equal to the partial electronic charges of the lowest occupied molecular orbital (LOMO). A new class of isocodal atoms (atoms having the same number of SRWns) was observed, i.e., atoms that become isocodal only at n ⩾ 1. A number of open questions following from these findings were formulated, including the possibility for a topological modeling of electron correlation. © 1993 John Wiley & Sons, Inc.
Computational studies of peripheral ring twisting in meso‐N‐methyl pyridyl‐substituted porphyrins
Authors: Monaco Regina R. , Zhao Ming 
Published: January 2005

AbstractSemiempirical molecular orbital calculations for the porphyrins tetrakis(4‐N‐methyl pyridyl)porphine (H2TMpyP‐4) and tetrakis(2‐N‐methyl pyridyl)porphine using the MNDO and AM‐1 Hamiltonians suggest that twisting one or more of the pyridinium rings results, at considerable energy expense, in highly nonplanar macrocycle configurations as the exocyclic ring(s) approach coplanarity. The results imply that the mechanism of intercalation of H2TMpyP‐4 into DNA cannot require twisting the exocyclic rings anywhere close to coplanarity with the central porphine core, but involves, instead, the inherent flexibility of DNA itself. © 1993 John Wiley & Sons, Inc.
Perturbation–variational methods revisited
Authors: Chacon Monique Revoredo , Zerner Michael C. 
Published: January 2005

AbstractWe describe a simple expansion of the Krylov type for the estimation of the electronic correlation energy of the ground state of closed‐shell systems and show its relationship with Brillouin–Wigner perturbation theory. We demonstrate the Brillouin–Wigner perturbation theory can be quickly solved in a noniterative fashion. Examples are presented using the intermediate neglect of the differential overlap model Hamiltonian (INDO/1), which indicates that this scheme captures well over 95% of the configuration interaction over double excitations method (CID) in a fraction of the computational effort. © 1993 John Wiley & Sons, Inc.
Decomposition and interpretation of the SCF interaction and deformation energies by the modified Pauli Blockade method
Authors: Pecul Krzysztof 
Published: January 2005

AbstractThe SCF interaction energy in He … Li+, (H2O) … HOH, and OC … BH3 complexes is decomposed, using the original and modified‐by‐the‐author Pauli Blockade (PB) method of Gutowski and Piela. The changes of the dipole moment of the deformed constituents are similarly decomposed and discussed as some indices of the deformation. The deformation is due mainly to the electrostatic interaction, but in some cases, the valence repulsion deformation effects are dominant. The comparison of the PB technique with some other decompositions is discussed. The PB methods seem to be more widely applicable, e.g., they are applicable for small intermolecular distances and large basis sets. The modified PB method is less‐time consuming than is the original one. © 1993 John Wiley & Sons, Inc.
A scheme for representation matrices of a permutation group using spin‐paired functions
Authors: Kadolkar C. , Sarma C. R. , Ghosh Dipan K. 
Published: January 2005

AbstractIn the present note, a linked form of spin‐paired functions for an N‐electron system in spin state S is suggested. This is found to lead to a simple scheme for generating the representation matrices of the elements of permutation group without searching for linkages in the superposition diagrams. The program based on this is found to generate the representation matrices more efficiently than do currently available procedures. © 1993 John Wiley & Sons, Inc.
Three stages of optimization and simple correlated wave functions
Authors: Hoor Marten J. Ten 
Published: January 2005

AbstractIt is advocated to carry out an optimization procedure, which is based upon the variational method, in such a way that the optimum values of the variational parameters are expressed as functions of physical constants, such as the atomic number, Z. The three stages involved in this treatment are illustrated by the optimization of nine correlated wave functions, which describe the ground states of atomic two‐electron systems. An analysis of the Z‐expansions of the total energies associated with these functions leads to the concept of a class of variational functions. The performances of functions belonging to the same class differ only marginally, especially at larger values of Z. Consequently, the concept of class may be used to bring some order in the plethora of variational functions. © 1994 John Wiley & Sons, Inc.
Substituent effects on chemical hardness
Authors: Kneisler John , Zhou Zhongxiang 
Published: January 2005

AbstractIt is shown that for a number of molecules there exists a Hammett‐like equation for the chemical hardness or the HOMO‐LUMO energy gap. Substituent effects can be factored out of the molecular hardness. Preliminary results show that a hardness substituent constant, similar to the Hammett σ‐constant, can be defined and determined for each substituent. © 1994 John Wiley & Sons, Inc.
A PM3 study of the critical distance factor in the activation/cyclization of selected Neocarzinostatin analogs
Authors: Mitra Abhijit , Capitani J. F. 
Published: January 2005

AbstractSemiempirical MOPAC RHF/PM3 and BIRADICAL/PM3 calculations are performed on several selected analogs of the Neocarzinostatin chromophore. The critical distance parameter, heat of formation, and pertinent bond orders are reported for each model compound. Heats of reaction are also reported for the cyclization of several model compounds to their corresponding diradical products. It is suggested that 3.49 ÅR represents an upper bound to the critical distance in the cyclization of compound related to Neocarzinostatin chromophore. © 1994 John Wiley & Sons, Inc.
Molecular electrostatic charge models: A topographical approach
Authors: Shrivastava Indira H. , Gadre Shridhar R. 
Published: January 2005

AbstractElectrostatic charge models for molecules have been developed by employing the critical topographical features of the molecular electrostatic potential (MESP) as the “fitting” criterion. These models include one or more spherical Gaussians for incorporating the continuous electron‐charge distribution in addition to the positive valued point charges representing the nuclei. The model parameters (point charges, the orbital exponents, and Gaussian centers) are optimized so as to mimic the extremal characteristics of the corresponding quantum chemicalMESP. The test cases reported here include methane, ethylene, and methanol molecules. The charge models developed using the present method are seen to satisfactorily reproduce the ab initioMESPand its extremal features. © 1994 John Wiley & Sons, Inc.
An efficient method for calculating static polarizabilities from a correlated wave function
Authors: Chacon Monique Revorêdo , Zerner Michael C. 
Published: January 2005

AbstractWe present a method closely related to configuration interaction over single excitations (CI‐S) for the calculation of static dipole moments and polarizabilities, which we call modified configuration interaction over single excitations (MCI‐S). This method allows for orbital relaxation through the inclusion of single excitations on a correlated first‐order Rayleigh–Schrödinger wave function. An approximation to our MCI‐S results in an inexpensive method to calculate polarizabilities that yields good results when compared with the full configuration interaction (CI‐F) results. This method, called modified configuration interaction over single excitations without triple excitations (MCI‐S_WT), seems particularly suitable to applications for large systems. Examples are presented using the intermediate neglect of the differential overlap model Hamiltonian (INDO/1), which indicates that the MCI‐S_WT procedure presents an error of less than 15% with respect to the CI‐F values in a fraction of the computational effort. © 1994 John Wiley & Sons, Inc.
Chemical signed graph theory
Authors: Lee Shyi‐Long , Li Chiuping 
Published: January 2005

AbstractChemical signed graph theory is presented. Each topological orbital of an N‐vertex molecular graph is represented by a vertex‐signed graph (VSG) that is generated by assigning a sign, either plus or minus, to the vertices without solving the secular matrix equation. The bonding capacity of each VSG is represented by its corresponding edge‐signed graph (ESG) and is quantified by the net sign of the ESG. The resulting 2N–1 configurations of VSGs can be divided into several groups according to the net signs of the corresponding ESGs. Summation of an appropriate set of degenerate VSGs is found to yield the conventional, canonical molecular orbitals. The distribution of the number of VSGs with respect to the net sign is found to be binomial, which can be related to bond percolation in statistical physics. © 1994 John Wiley & Sons, Inc.
Ab initio studies on the mechanism of the cycloaddition reaction between ketene and allene
Authors: Fang De‐Cai , Fu Xiao‐Yuan 
Published: January 2005

AbstractThe mechanism of the cycloaddition reaction between ketene and allene to form methylene–cyclobutanones has been studied theoretically by HF/3–21G and MP2/3–21G. These two reactions are believed to be unsynchronous and concerted, taking place through the twisted transition states. Four orbitals are mainly involved in each reaction, which is a “2 × [1 + 1]”‐type cycloaddition. The activated barrier for the two reactions are 27.2 and 27.1 kcal/mol, respectively, at the level of MP2/6–31G* based on the MP2/3–21G geometries, i.e., these two reactions are compatible. © 1994 John Wiley & Sons, Inc.
Origin of steric hindrance in ethane
Authors: Tokiwa Hiroaki , Ichikawa Hiroshi 
Published: January 2005

AbstractSteric hindrance has been regarded as a result of nonbonding atomic repulsion and measured in terms of empirically obtained van der Waals radii. The authors sought the cause of steric hindrance using the partial derivatives of the energy‐components with respect to a nuclear coordinate. The results show that electrostatic interactions do not produce steric hindrance but the restriction on electron‐movement does. Namely, the kinetic energy pressure is the first cause of steric hindrance. © 1994 John Wiley & Sons, Inc.
Numerical computation of bounded states for schröudinger operators
Authors: Núñez Marco A. 
Published: January 2005

AbstractA method developed previously for computing eigenfunctions of one‐dimensional Schrödinger operators is extended to Schrödinger operators in L2(R3N). It is known that in many cases these operators have not a compact resolvent; therefore, the convergence in L2(R3N) of the more used methods for computing the eigenfunctions is not guaranteed. The idea of the present method consists of replacing the eigenvalue problem in L2(R3N) by one corresponding to the system confined into a box Ω with impenetrable walls [Dirichlet problem in L2(Ω)]. It is shown that the eigenfunctions of the unbounded system can be approximated by those of the confined system when the box Ω is expanded. On the other hand, it is proved that the Schrödinger operator associated to the confined system has a compact resolvent and its corresponding sesquilinear form is bounded and elliptic in the Sobolev space W2,10(Ω). These properties guarantee the convergence in L2(Ω) of the standard methods to solve the Dirichlet problem: the Ritz method as well as the finite‐element and finite‐difference methods. Therefore, the eigenfuncions of the unbounded system can be approximated in L2(R3N) by means of the numerical solutions of the Dirichlet problem in L2(Ω) with sufficiently large Ω. This property guarantees the accurate computation of the true expectation values. © 1994 John Wiley & Sons, Inc.
Theoretical prediction of the Infrared and Raman spectra of O‐ethyl S‐2‐diisopropylaminoethylmethylphosphonothiolate
Authors: Hameka Hendrik F. , Jensen James O. 
Published: January 2005

AbstractWe have extended our computations of the structure and of the infrared and Raman spectra of methylphosphonates and related compounds to the O‐ethyl S‐2‐diisopropylaminoethylmethylphosphonothiolate molecule (we abbreviate the name to ESD). We have computed the optimized geometry and the vibrational infrared and Raman frequencies of ESD by means of the Guassian 92 Program Package using 6–31G* basis sets. We assign the vibrational frequencies and we correct each frequency by multiplying it with a previously derived 6–31G* correction factor. The result is a computer‐generated prediction of the IR and Raman spectra of ESD. The agreement between our theoretical predictions and the experimental IR spectrum of ESD is surprisingly good. © 1994 John Wiley & Sons, Inc.
Multiple solutions of the single‐reference coupled‐cluster equations. I. H4 model revisited
Authors: Jankowski K. , Kowalski K. , Jankowski P. 
Published: January 2005

AbstractSingle‐reference coupled‐cluster methods corresponding to various approximate forms of the cluster operator including up to four‐electron operators are applied to the simple H4 model system with the aim of numerically studying the attainability and properties of multiple solutions of the systems of nonlinear equations for the cluster amplitudes. Various solutions have been obtained for the excited states 21 A1 and 51 A1. It is documented that there exist nonphysical nonstandard solutions that yield energies very close to the physical ones. A simple way of selecting the physically meaningful solutions is proposed. It is demonstrated that the attainability of nonstandard solutions describing a state of H4 within the framework of a given SE‐CC method strongly depends on the cluster structure of that state. © 1994 John Wiley & Sons, Inc.