bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inclusion of relativistic effects into ZDO methods. IV. Relativistic CNDO/1
Authors: Boča Roman 
Published: January 2005

AbstractA relativistic, four‐component version of the CNDO (complete neglect of differential overlap) method is introduced. This method spans the class of zero‐differential‐overlap approximation and it utilizes a nonempirical parametrization based on results of atomic Dirac‐Fock calculations. The spin‐orbit splitting is included implicitly using the relativistic basis set which distinguishes Slater‐type functions of the lower and higher component spinors. The method is applicable to closed‐shell as well as to open‐shell systems. The actual version used is the R‐CNDO/1χ with a variable scaling approach. Applications to molecular geometries, ionization potentials, and energies of spin‐orbit splitting are demonstrated for AH, AH2, AH3, MH, InX, and HgI2 molecules at the self‐consistent‐field level as well as in the second order of the many‐body perturbation theory.
Differentiability of degenerate electronic wave functions with respect to parametric variables
Authors: Yin Li , Goscinski Osvaldo 
Published: January 2005

AbstractThe present paper is aimed at differentiability of electronic wave functions, with respect to parametric variables, in the presence of electronic degeneracy. An analysis is made of a wave function, constructed so that it has the largest domain of parameter space in which it is differentiable, with the help of Berry's formula for the geometric phase. In particular, the electronic wave functions, in presence of a double degeneracy in two‐ and three‐dimensional parameter spaces, are studied in detail. It was found that the three‐parameter‐dependent wave function is differentiable everywhere except along an axis starting from the degenerate point where it is discontinuous. The two‐parameter‐dependent wave function is differentiable everywhere except at the degenerate point where it is disocontinuous. These singularities are expected to have consequences on wave functions having parametric variables as arguments.
The atomic three‐body problem. An accurate lower bond calculation using wave functions with logarithmic terms
Authors: Kleindienst H. , Emrich R. 
Published: January 2005

AbstractAccurate lower and upper bounds for the nonrelativistic ground state energies E0 of the real systems 4He, H−, D−, and T− were calculated by the method of variance minimization using wave functions which include logarithmic terms. In addition, an analogous treatment with an infinite mass approximation for H−, He, and the isoelectronic series up to Z = 10 was carried out. Especially for H− and He the results (a.u.) are given by

These values have an absolute error smaller than 1.28 · 10−4 cm−1 for H−1and 3.10 · 10−9 cm−1 for He. Moreover it is shown that a variation of nuclear mass mn for the H− species does not produce a second discrete eigenvalue.
Partitioning of the Hamiltonian operator in the lie algebra formalism. Applications to the generalized brillouin theorem and the open‐shell Hartree‐Fock approximation
Authors: Koutecký Jaroslav , Scheuch Carsten 
Published: January 2005

AbstractThe Born‐Oppenheimer spin‐conserving Hamiltonian operator expressed in terms of the Lie algebra generators is partitioned according to the number of connected lines in the corresponding graphical representation. A simple derivation of some basic relations with the generalized Brillouin theorem, HF approach, and random phase approximation is presented.
Theoretical basis and design of the PPP model Hamiltonian
Authors: Jug Karl 
Published: January 2005

AbstractThe LCAO method is used for a discussion of the π electron approximation. The Hückel method is presented and rephrased on the basis of Löwdin orthogonalized orbitals. The background of the Pariser‐Parr‐Pople model Hamiltonian is illuminated and the method is derived from first principles. The parametrization is discussed and the scope reviewed.
Comparison of GVB and AMO approaches to the study of the PPP model of butadiene
Authors: Pauncz Ruben , Číž;ek JiřÍ 
Published: January 2005

AbstractThe purpose of this article is the comparison of generalized valence bond (GVB) and the alternant molecular orbital (AMO) techniques both in the localized and delocalized form. The model we have chosen is the PPP model of cis‐butadiene which is relatively simple and transparent. For equal bond lengths the AMO using delocalized orbitals is better than the GVB. For physical distances of the atoms these methods are of comparable accuracy. With the extension of the length of the central bond the GVB becomes better and is exact in the limit of two ethylenes. The AMO method using localized orbitals always gives the worst result of the three. In the limit of two ethylenes AMO in the localized and delocalized forms give the same error.
Application of the PPP method to the calculation of ionization potentials and electron affinities of conjugated organic molecules
Authors: Selsby R. G. , Pennance Philip , Barnhard K. I. 
Published: January 2005

AbstractBy making the atomic effective charge self‐consistent with the molecular charge density, it is shown that the PPP method can accurately predict the ionization potential and electron affinity computed as an energy difference of separately minimized ground and ionized states. The calculation is applied to a large variety of conjugated organic molecules, including heterocyclic systems and π‐electron‐contributing substituent groups.
A tensor representation of the real spherical functions for the continuous group O in cartesian coordinates: Example of eulerian rotations
Authors: Boudeville Yves , Rousseau‐Violet Jeanne 
Published: January 2005

AbstractThe aim of this article is to give a practical way for the use of real spherical functions in another frame than the frame in which they have been defined. For instance, we calculate physical properties from a local frame and use them in the general frame, deduced one from the other by Eulerian rotations on the coordinates. The power of the method is in the use of cartesian coordinates and in the definition of a scalar product between these functions to set up the complete vectorial space generated by these representations of the group O.
Dependence of valency on geometry for configuration interaction wave functions
Authors: Siddarth Prabha , Gopinathan M. S. 
Published: January 2005

AbstractEarlier definitions of valencies of atoms, molecules, and molecular orbitals are extended to configuration interaction (CI) wave functions. Using these definitions, valencies both at equilibrium and nonequilibrium geometries of molecules are calculated at the CI level and compared with non‐CI results. CI valency correlation diagrams are obtained. Valency variation with bond length using correlated wave functions is found to behave properly unlike in the case of SCF wave functions.
Upper and lower bounds to the Schrödinger equation eigenvalues
Authors: Fernández Francisco M. 
Published: January 2005

AbstractA method is presented for obtaining rapidly convergent upper and lower bounds to the eigenvalues of the Schrödinger equation for one‐dimensional and central‐field models. The logarithmic derivative of the wave function is written as a Padé approximant and the bounds are obtained by simply counting the real zeroes of the denominator.
A CI pseudopotential‐based description of the low‐lying states of Ag O2
Authors: Bravo G. , Flores‐Riveros A. , Novaro O. 
Published: January 2005

AbstractExtensive SCF‐LCAO‐MO variational and perturbative configuration interaction (CI) calculations framed within an effective core potential approximation have been performed to determine the two experimentally observed geometrical isomers of Ag O2 and the interconversion route between them. These structural forms, associated to the ground‐state local minima, yield virtually the same energy, and their spontaneous interconversion is strongly indicated, which agrees fairly well with the experimental measurements. The reaction Ag + O2 → Ag O2 was theoretically analyzed along a CI fully optimized energy pathway for the ground and various excited states, within C2v and Cs symmetry. Although a tight‐ion pair (A O) character is predicted for the ground state at the equilibrium geometries, its dissociation leads to neutral rather than to ionic fragments. The study of the reaction path within Cs symmetry shows an avoided crossing between the ground state and another 2A″ potential curve where the former correlates adiabatically with the reactants Ag(2S) + O2(1Δg). This indicates that the formation of the complex proceeds via a reactive state of molecular oxygen. The higher 2A″ electronic curves correlate with the metal 2P excited state, and the oxygen binding is found to be less favorable. The present results are shown to have an important bearing on the experimentally known catalytic properties of oxygen adsorbed on silver surfaces.
Non‐radiative deactivation of molecules. II. Theoretical study of the internal conversion rates in azulene
Authors: Gustav Klaus , Storch Michael 
Published: January 2005

AbstractBased on completely optimized molecular geometries of the photophysically relevant electronic states, the corresponding vibrational energies and wave functions and the theoretical rate constants for the internal conversion processes of azulene within the Sp, term system are presented. The influence of the promoting and accepting modes on the radiationless deactivation rates is discussed. An analysis of the active nonradiative modes is given. In context with the respective theoretical radiative rates, the efficiency of the different azulene fluorescences is interpreted.
Electrostatic potential mapping of polycyclic aromatic hydrocarbon diol epoxides using a dipole
Authors: Kumar Anil , Mishra P. C. 
Published: January 2005

AbstractElectrostatic potential maps of benz(a)anthracene diol epoxide, benzphenanthrene diol epoxide, chrysene diol epoxide, and tryphenylene diol epoxide, which are ultimate carcinogens derived from the corresponding polycyclic aromatic hydrocarbons, have been studied using a dipole of length 1 Å and strength 1 Debye. The net charge distributions in the molecules were obtained using the MNDO molecular orbital method. The maps were drawn for two closest distances of approach between the charged ends of the dipole and atoms of the molecules. Using the electric field directions and values of electrostatic potentials, reactive sites and relative reactivities of these molecules have been examined. Existence of a bay region appears to be important for the carcinogenic activity of a diol epoxide in this class of carcinogens.
Solvent effects on mechanism of tetramethylene polymerization
Authors: Jug Karl 
Published: January 2005

AbstractThe polymerization mechanism of tetramethylenes was reinvestigated under inclusion of solvent effects. The approach of a methanol molecule to a borderline diradical, a typical diradical, and a typical zwitterion was studied by a valence, charge, and dipole moment analysis of SINDO1 calculations. Whereas the solvent molecule has no effect on the character of the zwitterion, the borderline diradical was found to switch to a zwitterion at the approach of the methanol molecule if the distance between the donor carbon and the methanol oxygen is below 2 Å. A similar switch of character was observed for the typical diradical at CO distances below 1.5 Å. From energy considerations it is concluded that borderline diradicals can follow a zwitterionic polymerization mechanism in polar solvents, whereas typical diradicals are much less likely to do so.
Theoretical approach to reactions of polyatomic molecules
Authors: Zülicke L. , Merkel A. 
Published: January 2005

AbstractA scheme for systematic reduction of the theoretical treatment of elementary reactions involving polyatomic molecules is described; it consists of (1) limitation to the energetically relevant regions of the nuclear configuration space (the reaction path and its near environs) and (2) restriction to the dynamically relevant subspace of the nuclear configuration space (the active modes). Starting from a generalized reaction path Hamiltonian of Nauts and Chapuisat allowing for the use of arbitrary curvilinear coordinates and several large‐amplitude modes, the realization of the above‐sketched scheme is discussed. A compilation of recent work along these lines, mostly based on the simplified Miller‐Handy‐Adams reaction path Hamiltonian, is given with particular emphasis on applications of a statistical adiabatic model.
MNDO CI study of the photoisomerization about polar double bonds
Authors: Ertl Peter 
Published: January 2005

AbstractCis‐trans photoisomerization of ethylene, some of its methyl and fluoro derivatives, methaniminium, and aminoborane was studied and twisted biradical geometries of these molecules in So, S1, and S2 states were optimized using the half‐electron version of the MNDO method with configuration interaction. The results are quite satisfactory, in good agreement with available ab initio data.
Quantum chemical calculations of silicon clusters in silicon dioxide and point defects in β‐cristobalite
Authors: Gadiyak G. V. , Korolenko I. V. , Morokov Yu. N. 
Published: January 2005

AbstractA local electronic‐state density in β‐cristobalite in the empirical tight‐binding approximation has been calculated by the recursion method. In particular, silicon clusters have been considered in β‐cristobalite containing up to three coordination spheres of silicon atoms.
Graph theory of synthons
Authors: Kvasnička V. , Pospíchal J. 
Published: January 2005

AbstractA graph‐theory model of synthons is suggested. A synthon is a special kind of the molecular graph in which some vertices are distinguished from other ones, and they are called the virtual vertices. The most important property of the synthons is that the constraint of strict stoichiometry is removed and the virtual vertices formally correspond to functional groups that are not closely specified.
QCT study of isotopic effects in H + HBr abstraction and exchange reactions
Authors: Tiňo Jozef , Urban Ján , Klimo Viliam 
Published: January 2005

AbstractThe method of quasi‐classical trajectories on an LEPS hypersurface was used for studying the influence of the exchange of one or both of the hydrogen atoms for deuterium in the reaction H1 + H2Br. As expected, the reaction cross sections of the exchange and abstraction reactions were found to increase if H1 was replaced by D and decrease if H2 was replaced by deuterium. A similar change in the reaction cross sections have also been observed for vibrationally excited reactants. The distribution of vibrational (rotational) energy is related to the ωe (Be) values of the respective reactants and products.
Theoretical study of the reaction Ne + H+2 → NEH+ + H in the 2A′ ground state
Authors: Urban J. , Jaquet R. , Staemmler V. 
Published: January 2005

AbstractA three‐dimensional potential energy surface for the 2A′ ground state of the system (NeH2)+ (2Σ+ in collinear geometry) has been calculated at SCF and CEPA levels. This surface describes the abstraction reaction

which is endoergic by 0.57 eV (ΔH00) and has been studied recently by different experimental groups at low collision energies. Our CEPA calculations yield an endoergicity of 0.55 eV (ΔH00). The 2A′ surface has a minimum at collinear geometry with RNe—H = 2.29 a0 and RHH = 2.08 a0 and a well depth of 0.49 eV relative to Ne + H+2. The effects of electron correlation on the shape of the surface and on the well depth are discussed.An analytic fit of the collinear part of the surface has been constructed based on Simon's proposal of using polynomials in the coordinates (RRe)/R instead of (RRe). The fitted potential is used for quantum mechanical scattering calculations with the finite element method (FEM). Preliminary results for reaction probabilities for H+2 in different vibrationally excited states are given and compared to the experimental results.
Density matrix of crystalline systems. I. Long‐range behavior and related computational problems
Authors: Pisani C. , Aprà E. , Causà M. 
Published: January 2005

AbstractThe one‐electron density matrix (DM) of crystalline systems is discussed, especially concerning its longrange behavior; reference is made throughout to systems treated at a Hartree–Fock–LCAO–SCF level of approximation. The analysis is performed on the assumption of generally smooth behavior of eigenvalues and eigenvectors in k (reciprocal) space, so that they can be expressed by means of a truncated Fourier expansion. This assumption allows us to obtain analytic approximations for the DM, on the basis of the information collected at a few, suitably selected sampling k points. It is therefore possible at the same time to discuss the influence of structural parameters (dimensionality of the system, existence and shape of the Fermi surface, structure of the chemical bonds) and to set up a computational scheme that is general and simple enough.
Physical quantification of the biological effectiveness of ionizing radiations
Authors: Watt D. E. , Kadiri L. A. 
Published: January 2005

AbstractThe role, and limitations, of the fundamental physical quantities used in our current system of dosimetry for the protection of individuals against the hazardous effects of ionizing radiation is discussed briefly. A major limitation is the inability to correlate biological data, in a unified way, as a function of linear energy transfer with the consequent necessity for quality factors.From consideration of the various interaction processes undergone by charged particles in the equilibrium slowing down spectra generated by the incident radiation field, it is shown that good correlation of biological effects, for all radiation types, can be achieved in terms of linear primary ionization. The implication is that delta‐ray effects play at most a very minor role, at moderate fluences, and that, consequently, the absorbed dose is an unsuitable parameter for describing radiation effects. Structure in the radiosensitive targets is observed to have a critical dimension of about 2 nm. It occurs only when double‐stranded DNA is present and the magnitude of the inactivation probability is consistent with double‐stranded breaks being the significant lesion. Calculation is made of the yield of lesions as a function of the mean free path for primary ionization.Differential spectra of radiation quality are obtained for monoenergetic electrons (0.2 keV to 30 MeV); for characteristic X‐rays from carbon, aluminium, neon, potassium, copper, silver, and tungsten; for 50 kV X‐rays, 250 kV X‐rays, 241Am, 137Cs, and 60Co gamma rays; and for neutrons with energies between 0.1 and 50 MeV. Damage by electrons is shown to be predominant at the ends of their tracks between 50 and 200 eV, whereas this is not so for the proton recoil spectrum generated by neutrons above 1 MeV.Proposals are made for a unified system of dosimetry that is independent of radiation type and that obviates the need for quality factors. The method is thought to be of general applicability to irradiations by nuclides incorporated into mammalian cells, by ingested emitters, and by external sources.
Tunnel effect in proton transfer
Authors: Esquivel J. L. , Mata‐Segreda J. F. 
Published: January 2005

AbstractSemiempirical computations were carried out to determine the tunneling rates in the case of coupled motion of two protons along the reaction coordinate. The following molecular systems were studied for medium intermolecular distances (A—B = 2.72 or 2.75 Å); +AH—BH—A, where A was NH3 or H2O and BH was HF or H2O. In the cases where the bridge was HF, solvation was modeled with just one water molecule attached to each side of the perpendicular axis through HF at 2.75 Å. Coupled motion of three protons was also included in the case of H3O—H2O—H2O—H2O.
Application of molecular orbital graph theory to vibrational problems of finite chain systems
Authors: Lü Tianxiong , Tachibana Akitomo , Yamabe Tokio 
Published: January 2005

AbstractA generating function approach based on molecular orbital graph theory is presented that provides a straightforward way of obtaining the secular polynomials and energy bands for repeated unit systems from polynomial recurrence expressions. The possibility of obtaining the analytical energy‐level spectrum of the system can also be predicted. These results are then used to discuss the vibrational problems of finite chain systems with single‐ and double‐component lattices. It seems to be the first report describing the vibrational states of an (AB)N chain.
Modeling of real 20‐component protein chains: Determination of the electronic density of states of aperiodic seven‐component polypeptide chains containing strongly different amino acid residues
Authors: Bakhshi A. K. , Otto P. , Liegener C.‐M. , Rehm E. , Ladik J. 
Published: January 2005

AbstractTo model a real 20‐component protein chain, the results of the electronic density of states (DOS) of seven‐component periodic and aperiodic polypeptide chains calculated on the basis of ab initio matrix block negative factor counting method are presented. The seven amino acid residues taken into account are rather different: glycine, serine, cysteine, asparagine, histidine, aspartic acid, and tryptophane. In the case of aperiodic chains, the energy states are found to be distributed over a much wider range of energy than in the corresponding periodic chains. In the intrinsic state, both periodic and aperiodic polypeptide chains are predicted to be insulators. The effect of the block copolymerization on the DOS distribution and the band gap values of both periodic and aperiodic polypeptide chains has been also investigated. Finally, the methods to calculate from the DOS curves hopping conductivities and the possibilities to compare them with experiment are outlined.
Theoretical study of single‐electron capture in the N5+ + He and O6+ + He collisions by means of ab initio methods
Authors: Bacchus‐Montabonel M. C. , Amezian K. 
Published: January 2005

AbstractPartial cross sections of single‐electron capture on the n = 3 levels have been determined theoretically for the N5+ + He and O6+ + He collisions by means of a semiclassical method using ab initio potential energy curves and radial and rotational coupling matrix elements. The different behavior of these two isoelectronic systems is fairly well reproduced by our calculations.
Density functional calculation of transition metal cluster energy surfaces
Authors: Beznosjuk S. A. , Dajanov R. D. , Kuldjanov A. T. 
Published: January 2005

AbstractA quantum field mechanics of an electron subsystem in 3D physical space as the topology of compact atomic clusters with spontaneously broken local canonical symmetry is used for investigation of different types of microdefects in the condensed state of transition metals. The theory is illustrated with results of calculation of small compact Fen clusters (n = 2, 6, 14).
Molecular point symmetry and the phase of the electronic wave function: Tools for the prediction of critical points of potential energy surfaces
Authors: Mezey Paul G. 
Published: January 2005

AbstractBy combining a well‐known theorem of Longuet‐Higgins on the phase changes of electronic wave functions along loops encircling a conical intersection of potential surfaces, and a recently proven “vertical symmetry theorem” on the relative distributions of point symmetry groups and potential surface critical points in configuration space, a new result is obtained, suitable for the prediction of the presence of a critical point within a domain of configurations.