bluuebunny/crossref_metadata_2025_split huggingface dataset:
MNDO calculation of reaction heats determininig the mechanism of antioxidant action of the phenols in polyolefins
Authors: Bolotin A. , Pipiraité P. 
Published: January 2005

AbstractThe quantum chemical substantiation of antioxidant action of the substituted phenols in polyolefins is presented. The electronic structure of the phenols, phenoxy radicals, and model products of polyolefin destruction was calculated by the MNDO method. On the basis of the presumed chemical reactions, the electronic structure criteria determining the antioxidant activity are selected. These are the O—H bond dissociation energy in phenols and the charge on the atoms of π‐system in phenoxy radicals. The competition between these reactions takes place, and the calculation of the reaction heats shows that the reactions with the formation of the substituted quinones are in preference to the reactions in which the peroxycyclo‐hexadienones are formed.
Optimization of molecular electronic structure calculations. 1. Local symmetry and local symmetricized orbitals
Authors: Kovrikov A. B. 
Published: January 2005

AbstractA formalism is suggested of the so‐called local symmetricized orbitals to be used for the construction of a symmetricized basis in molecular electronic structure calculations. The local symmetricized orbitals are defined as additive contributions to the symmetry orbitals of a molecule that arise from symmetry operations of a corresponding atom. The local symmetricized orbitals are transformed according to the irreducible representations of the molecular symmetry group. This approach appears to be most suitable for the optimization of quantum mechanical calculations accounting for the spatial symmetry of compounds under consideration. This fact is due to the formalism of the local symmetricized orbitals that explicitly accounts for the local symmetry of basis function centers, which is essential for such optimization.
Sur une tentative d'unification des théaories quantiques de la cancèrisation par les polyacènes: I. Thèorie des règions M, L, et B
Authors: Gayoso Jose , Kimri Said 
Published: January 2005

AbstractThis study is a unified approach to quantum theories of polyacen carcinogenesis. Part I discusses the M, L, and B regions theory. Although the M region of polyacens is much less reactive than is the K region, the chemical reactivity of these two regions parallels each other. Consequently, the K‐L Pullman's theory may be reformulated by replacing the K region by the M region. The M‐L regions theory improves all the quantum structure‐carcinogenic activity relationships obtained previously in the K‐L framework. Moreover, it would appear that in these correlations, the most important role is played by nonconcerted electrophilic reactions. We suggest that the M‐L modified Pullman's theory and the Bay (B) region theory, proposed by Jerina et al., are related to different steps of the metabolic activation mechanism leading to ultimate carcinogen: the first step for the Pullman's theory and the carbocation step for the theory of the Bay region. We have termed the “M, L and B regions theory” as this unified approach to the problem of polyacens carcinogenesis.
A study of hydration effects on the conformational aspects of gaba mediators
Authors: Majumdar D. , Guha Sephali 
Published: January 2005

AbstractThe conformation of numerous chemical compounds is strongly influenced by solvents. Knowledge of their structure in solution is necessary, especially for a discussion of the biological and pharmacological activity of the molecules. The neurotransmitters and their agonists and antagonists are known to be flexible molecules that interact with quite distinct receptors. The conformational properties of several GABA (γ‐aminobutyric acid) mediators have been studied by the MNDO technique. The optimized geometries of the molecules have been used to study the solvent effects on their conformational properties considering the supermolecule approach for their first hydration shell. A conjectural pharmacophoric pattern for several GABA inhibitors has already been suggested from the molecular electrostatic potentials (MEP) of several molecules using a localized bond orbital technique. In the present work, MEP calculations have been carried out considering a solvent effect on the MNDO optimized geometries to investigate any deviation from the earlier results.
The modeling of nucleophilic and electrophilic additions and substitutions using extended Hückel‐based reaction potentials
Authors: Daul Claude , Goursot Annick , Morgantini Pierre‐Yves , Weber Jacques 
Published: January 2005

AbstractA new formalism has been developed in order to evaluate intermolecular interaction energies for organometallic complexes including electrostatic, polarization, and orbital contributions based on extended Hückel molecular orbital (EHMO) theory. The electrostatic interaction is evaluated using (i) a multipolar expansion of EHMO charge density, or (ii) by calculating directly the electrostatic integrals in the basis of atomic orbitals. The polarization effects are evaluated by introducing a perturbation into the Hamiltonian. The orbital interaction is calculated by considering a supermolecule made of the organometallic substrate and a model electrophile or nucleophile. To provide the shortest possible response time on an interactive computer graphics facility, this model should require the minimum amount of computer time, which explains why approximate procedures are used to evaluate the dominant contributions to the interaction energies. Preliminary results show that these interaction energies lead to reaction potentials in good agreement with experiment for a broad series of nucleophilic and electrophilic addition or substitution reactions involving organometallic complexes. In addition, it is shown that the method can easily be extended for the calculation of solvent effects. To this end, developments considering the supermolecule surrounded by a polarizable continuum are in progress.
Excited and ionized states of RuO4 and OsO4 studied by SAC and SAC‐CI theories
Authors: Nakatsuji H. , Saito S. 
Published: January 2005

AbstractThe excitation and ionization spectra of RuO4 and OsO4 are studied theoretically by the symmetry‐adapted cluster (SAC) and SAC‐CI theories. This is the attempt to assign whole of the spectra by ab initio calculations including electron correlations. In the ground state, electron correlations work to reduce the polarity of the M–O bond overestimated in the Hartree–Fock calculation. The Os–O bond is stronger than is the Ru–O bond, which is reflected in the differences of the excitation and ionization spectra of RuO4 and OsO4. The excitation energies of the experimental spectra are well reproduced by the SAC‐CI theory, though the calculated intensities of some peaks are very small in comparison with the experiments. The outer‐valence ionization spectra calculated by the SAC‐CI theory agree well with the experimental photoelectron spectra. Some shake‐up peaks that are accompanied with an electron‐transfers from oxygen to metal are also calculated.
The dynamics of equally spaced multilevel model systems
Authors: Amirav A. , Even U. , Jortner Joshua 
Published: January 2005

AbstractCoherent dynamics of multilevel systems is of interest for the elucidation of energy disposal and multiphoton chemistry of polyatomic molecules. We compare the analytical solutions for coherent multiphoton excitation of two sparse multilevel model systems: (1) The spin‐J system consisting of N = (2J + 1) equally spaced levels with the radiative coupling being determined by the xth component of the angular momentum. (2) The equally coupled N level system. The transition amplitudes for system (1) are always periodic, which is in contrast to the nonperiodic behavior exhibited by system (2) for N > 3.
Van der waals modulated spectral intensities: Application to infrared absorption
Authors: Linder Bruno 
Published: January 2005

AbstractA formulation is presented of the effects of van der Waals interaction on infrared intensities. The theory takes account of induction and dispersion interactions (including charge interpenetration) and is applicable to fluids of arbitrary density. The transition moments are developed from generalized van der Waals‐induced moments, and expressions are obtained for the adsorption coefficient in terms of generalized charge densities and charge‐density (hyper)susceptibilities. Explicit expressions are given also of the integrated absorption coefficient in terms of multipoles, and (hyper)polarizabilities and their derivates, and the usefulness of this formulationin interpreting experimental data is illustrated by several examples. The relevance of the induction and dispersion interactions to allowed and to forbidden transitions made allowed is discussed.
Dirac‐Fock self‐consistent field method for closed‐shell molecules with kinetic balance and finite nuclear size
Authors: Mohanty A. , Clementi E. 
Published: January 2005

AbstractWe present a general method of implementing the kinetic balance condition within the Dirac‐Fock (DF) self‐consistent field (SCF) formalism for closed‐shell molecular structure. We review the steps leading to the derivation of DF SCF equations for closed‐shell molecules, particularly as formulated by Matsuoka et al. In the present approach, the large component of the molecular spinors are expanded in terms of atomic basis spinors of spherical‐type Gaussian functions, with the small component related to the large component by the kinetic balance condition. It is shown that imposing the kinetic balance condition on geometric Gaussian‐type basis functions allows us to obtain the Fock matrix elements, involving both the large and the small components, form the standard nonrelativistic Cartesian‐type matrix elements. By using properties of orthogonal polynomials, the solid spherical harmonics are expressed in Cartesian form, thus providing a general basis for transformation of one‐ and two‐electron‐matrix elements, obtained from a Cartesian Gaussian‐type basis, to a spherical Gaussian‐type basis. The advantages of using kinetically balanced geometric Gaussian‐type basis functions in molecular DF calculations including finite‐size nucleus effects are emphasized. For the sake of completeness, we have added in an appendix corrections to the nuclear attraction matrix elements for the finite‐size nucleus already derived by Matsuoka.
Non‐local relation between kinetic and exchange energy densities in Hartree–Fock theory
Authors: March N. H. , Santamaria R. 
Published: January 2005

AbstractA non‐local generalization K(r, r') of the kinetic energy t(r) such that t(r) = ∫K(r, r') dr' is defined using the idempotency property of the Hartree–Fock first‐order density matrix. This is, in turn, related by means of an explicit differential equation to the non‐local exchange energy density X(r, r'). The relationship is illustrated for a couple of examples: with the Fermi‐hole in a uniform electron gas, of importance in the local density version of density functional theory, and with inhomogeneous electron systems.
Bonding in heteronuclear transition‐metal diatomics: NbIr
Authors: Castro Miguel , Keller Jaime , Mareca Pilar 
Published: January 2005

AbstractBonding in transition‐metal molecules presents novel features: (i) s electron bonding is overcome by multiple d electron bonding, (ii) intraatomic exchange favoring atomic magnetization competes with bonding that tends to pair the electrons, and (iii) in the heteronuclear dimers, the ionic terms may be important due to strong charge‐transfer effects. The NbIr heteronuclear diatomic molecule shows all these features clearly. The cellular multiple scattering‐xαβ calculation presented in this paper shows the ground state to correspond to antiferromagnetic coupling between the highly magnetic Nb atom and the Ir atom. A one‐electron charge transfer from Nb to Ir was found; the result is an ionic structure, Nb+Ir−, for the dimer. The computed equilibrium distance, 4.100 a.u., corresponds to a region where d bonding strongly overcomes the s bonding, which alone would have stabilized the molecule at 5.950 a.u. At intermediate interatomic separations, 5.35 a.u., the NbIr system has a state in which all molecular orbitals are bonding with a high hybridization between the ns and (n − 1)d electrons of each atom, resulting in a (almost entirely) covalent high multiple‐bond formation for this meta‐stable state of the dimer.
Electronic aspects of LADH catalytic mechanism
Authors: Tapia O. , Cardenas R. , Anders J. , Krechl J. , Campillo M. , Colonna‐Cesari F. 
Published: January 2005

AbstractElectronic aspects of the catalytic mechanism of liver alcohol dehydrogenase (LADH) are studied with the help of ab initio analytical gradient SCF MO methods. Three points are considered: (i) role of the catalytic zinc; (ii) geometry and electronic structure of the transition state for the hydride transfer reactions; and (iii) factors affecting the energy gap for the hydride transfer step, namely, substrate binding to zinc, reaction field, and serine 48 effects on the potential energy profile. The coordination sphere of the catalytic zinc has been modeled with an ammonia molecule and two SH− groups; complexes with CH3O−, CH3OH, and CH2O have been studied; a (6, 2, 2, 2, 1/6, 2, 1/3, 2) basis set has been used for Zn++; a (5, 2, 1, 1/3, 2) was used for oxygen, carbon, and sulfur; and a (3, 1) was used for hydrogen atoms. The hydride step was studied with two model systems: pyridinium cation/1,4‐dihydropyridine coupled to the CH3O−/CH2O reaction, and cyclopropenyl cation/cyclopropene coupled to the CH3O−/CH2O system. For the latter, the role of Ser48 has been studied at the supermolecule level. The calculation on the hydride transfer step has been done at a 4–31G basis set level. The results obtained shed new light on the sources of catalytic activity of liver alcohol dehydrogenases.
Hydrogenlike atoms in uniformly charged sphere model of atomic nucleus. II. Application of basis‐set expansion method
Authors: Matsuoka O. , Fujimura N. , Hasegawa T. 
Published: January 2005

AbstractThe basis‐set expansion method has been applied to the nonrelativistic and relativistic ground states of one‐electron atoms H, Ar17+, Xe53+, Hg79+, and U91+ in the uniformly charged sphere (UCS) and the point‐change (PC) models of atomic nucleus, using the Gaussian‐type basis functions. The energies and the radial expectation values, especially 1/r2, converges faster in the UCS model than in the PC model. In the PC model, larger values of the exponent parameters of the basis functions are required both in the nonrelativistic and the relativistic calculations. Even in the UCS model, the larger values of the exponent parameters are needed in the relativistic calculations.
On a canonical functions approach to the elastic scattering phase‐shift problem
Authors: Kobeissi Hafez , Fakhreddine Khaled , Kobeissi Majida 
Published: January 2005

AbstractThe determination of the phase‐shift δρ(E) (related to a central potential V(r), a total energy E, and an angular momentum ρ) is considered. The “canonical functions” approach already used for the eigenvalue problem is adapted to that of δ. The conventional approach computes the radial wave function yρ(E;r) starting at rs ∼ 0 (with convenient initial values) and stepping on toward a large value r = R ∼ ∞, where yρ is matched to its asymptotic value yρ(R) ∼ a sin(kR – ρ π/2 + δρ) and δ is deduced. The present approach starts at any “origin” r0, replaces the use of the wave function y by that of the “canonical functions” α and β (well defined for given V, E, and ρ) and defines two functions q(r) and Q(r) in terms of α and β. When r → O, q(r) approaches a constant limit giving Q(r0), and thus the starting problem is avoided. Using this value Q(r0), the function Q(r) is generated for r > r0. The function Q(r) reaches a constant limit when r → ∞; this limit is precisely tan δ; thus, the “final” matching problem is avoided. The present method is applied to the Lennard–Jones potential function for low and high E and for low and high ρ. The comparison of the results of the present method with those of confirmed numerical methods show that the present method is competitive.
The rigorous (nonvariational) solution of the Schrödinger equation for a molecular potential of arbitrary shape. I. General formulation
Authors: Gegusin I. I. 
Published: January 2005

AbstractAn approach allowing us to solve exactly a Schrödinger eigenvalue problem for a molecular potential of arbitrary shape is developed. The method is based on an integral equation. The conditions, under which the original eigenvalue problem may be transformed into an algebraic one, are discussed. Owing to a special partitioning of space into cells, only some absolutely and uniformly convergent Green's function expansions are involved. As a consequence, all the algebraic manipulations are rigorously justified, in constrast to some direct generalizations of multiple scattering technique. Nevertheless, the method offered results in much the same secular equation, as one previously obtained [R. G. Brown, J. Phys. B 21, L309 (1988)]. The relationship between the present method and other approaches is discussed. The matching conditions between any two local representations of a true wave function, which are believed to be some extra and independent ones [E. Badralexe and A.J. Freeman, Phys. Rev. B 37, 10469 (1988)], are shown to result from a corresponding set of algebraic equations. Some computational aspects are also discussed. A preliminary result of the H2+ energy spectrum calculation is reported.
The rigorous (nonvariational) solution of the Schrödinger equation for a molecular potential of arbitrary shape. II. The basis functions, discrete spectrum, and the special case of MT potential
Authors: Gegusin I. I. 
Published: January 2005

AbstractThis paper continues Part I of this paper, referred to in the following as I. The construction of a basis set is explicitly presented. The special case of MT potential is considered, and the corresponding secular equation is shown to match exactly the one resulting from the well‐known scattered wave method. Finally, the bound states of a molecule are obtained as the solutions of a real‐valued matrix eigenvalue problem.
Higher analytic derivatives. I. A new implementation for the third derivative of the SCF energy
Authors: Colwell Susan M. , Jayatilaka Dylan , Maslen Paul E. , Amos Roger D. , Handy Nicholas C. 
Published: January 2005

AbstractThis is the first of a series of papers on the ab initio calculation of the second, third, and fourth derivatives of the energy with respect to nuclear coordinates. The knowledge of these derivatives yields anharmonic spectroscopic constants. Here, we present efficient formulae for the analytic evaluation of these derivatives for closed‐shell SCF wave functions. We discuss our implementation of the third derivative formula, in particular the integral and vectorization procedures. Applications are reported for H2S, CHOF, and HCCF.
Quasi‐particle equation from the configuration‐interaction (CI) wave‐function method
Authors: Casida Mark E. , Chong Delano P. 
Published: January 2005

AbstractThe Green‐function method is a well‐known way to reduce the quantum mechanical problem of n electrons moving in the field of clamped nuclei to the problem of solving a one‐electron Schrödinger equation (the quasi‐particle equation) involving a pseudopotential (the self‐energy). This method is widely used in solid‐state, low‐energy electron‐molecule scattering, ionization, and electron attachment theory, and much work has focused on finding accurate self‐energy approximations. Unfortunately, the operator nature of the fundamental quantity (Green function) in the usual quasi‐particle equation formalism significantly complicates the derivation of self‐energy approximations, in turn significantly complicating applications to inelastic scattering and multiconfigurational bound‐state problems. For these problems or wherever the operator approach becomes inconvenient, we propose an alternative quasi‐particle equation derived wholely within a configuration interaction wave‐function formalism and intended to describe the same phenomenology as does the Green function quasi‐particle equation. Our derivation refers specifically to electron removal but is readily generalized to electron attachment and scattering. Although the Green function and wave‐function quasi‐particle equations are different, we emphasize the parallels by rederiving both equations within the equations‐of‐motion formalism and then producing a wave‐function analog of the Green function two‐particle‐hole Tamm–Dancoff approximation.
Symmetry adapted formulation of the generalized Brillouin theorem
Authors: Godefroid M. , Lievin J. , Metz J.‐Y. 
Published: January 2005

AbstractThe singly excited functions satisfying Brillouin theorem are expressed as linear combinations of configuration‐state functions for any spin and spatial symmetries (atomic or molecular) and for any reference wave function. The generality of the formulation is ensured by the use of the irreducible tensor method that can be adapted to any symmetry point group of interest. The expansion coefficients are simply written as products of fractional parentage coefficients, spin‐ and orbit‐recoupling coefficients, and phase factors. The formalism is illustrated for some atomic (Kh) and molecular (C∞v, C3v, and Td) configurations. Group theoretical techniques are also used to correlate the Brillouin conditions within a chain of groups.
Midgap levels of photoexcited conductive polymers. I. A simple description of the midgap levels based on molecular orbital interaction
Authors: Tanaka Kazuyoshi , Yoshizawa Kazunari , Yamabe Tokio 
Published: January 2005

AbstractWe studied the midgap levels appearing in the photoexcited conductive polymers such as trans‐ and cis‐polyacetylenes, poly(p‐phenylene), polypyrrole, and polyacene based on the molecular orbital analysis. The midgap levels are constructed from the transformation of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the ground state. As the result of the localization of the wave functions associated with these midgap levels, large polarization is induced between adjacent carbon atoms. Based on the examination of the energy gap between the two midgap levels, the polymers with a nondegenerate ground state such as cis‐polyacetylene, poly(p‐phenylene), and polypyrrole would show no sizable photoconductivities.
Approximate noninteracting kinetic energy functionals from a nonuniform scaling requirement
Authors: Ou‐Yang Hui , Levy Mel 
Published: January 2005

AbstractWe have recently proven an inequality for the exact noninteracting kinetic energy density functional \documentclass{article}\pagestyle{empty}\begin{document}$ T_s [n]:\mathop {\lim }\limits_{x \to \infty } T_s [n_\lambda ^x] \le T_s [n_s^y [n] + T_S^2 [n] < \infty,where{\rm }n_\lambda ^x (x,{\rm }y,{\rm }z) = \lambda n(\lambda x,{\rm }\lambda {\rm y, }\lambda z) $\end{document}. It is known that the gradient expansion through fourth order, T[n], violates this inequality. Toward improving TsGE[n], we have constructed two new functionals, Ts1[n] and Ts2[n], by keeping the zeroth and second orders in TsGE[n] and replacing the fourth order with two simple terms, respectively, so that these new functionals satisfy the inequality. Numerical tests are presented for Ts1[n], Ts2[n], and TsGE[n] and for the gradient expansion through second order. Hartree–Fock and hydrogenic atomic densities are employed.