bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ab initio calculations of relativistic and electron correlation effects in polyatomics using the universal Gaussian basis set: XeF2
Authors: Malli Gulzari L. , Styszynski Jacek , Da Silva Alberico B. F. 
Published: December 2004

AbstractAb initio accurate all‐electron relativistic molecular orbital Dirac–Fock self‐consistent field calculations are reported for the linear symmetric XeF2 molecule at various internuclear distances with our recently developed relativistic universal Gaussian basis set. The nonrelativistic limit Hartree–Fock calculations were also performed for XeF2 at various internuclear distances. The relativistic correction to the electronic energy of XeF2 was calculated as ∼ −215 hartrees (−5850 eV) by using the Dirac–Fock method. The dominant magnetic part of the Breit interaction correction to the nonrelativistic interelectron Coulomb repulsion was included in our calculations by both the Dirac–Fock–Breit self‐consistent field and perturbation methods. The calculated Breit correction is ∼6.5 hartrees (177 eV) for XeF2. The relativistic Dirac–Fock as well as the nonrelativistic HF wave functions predict XeF2 to be unbound, due to neglect of electron correlation effects. These effects were incorporated for XeF2 by using various ab initio post Hartree–Fock methods. The calculated dissociation energy obtained using the MP2(full) method with our extensive basis set of 313 primitive Gaussians that included d and f polarization functions on Xe and F is 2.77 eV, whereas the experimental dissociation energy is 2.78 eV. The calculated correlation energy is ∼ −2 hartrees (−54 eV) at the predicted internuclear distance of 1.986 Å, which is in excellent agreement with the experimental Xe—F distance of 1.979 Å in XeF2. In summary, electron correlation effects must be included in accurate ab initio calculations since it has been shown here that their inclusion is crucial for obtaining theoretical dissociation energy (De) close to experimental value for XeF2. Furthermore, relativistic effects have been shown to make an extremely significant contribution to the total energy and orbital binding energies of XeF2. © 1995 John Wiley & Sons, Inc.
Electron correlation and relativistic effects in xenon tetrafluoride
Authors: Styszynski Jacek , Malli Gulzari L. 
Published: December 2004

AbstractAb initio all‐electron fully relativistic Dirac–Fock self‐consistent field and Dirac–Fock–Breit calculations are reported for the XeF4 molecule at various internuclear distances assuming the experimental D4h geometry with our recently developed relativistic universal Gaussian basis set. The nonrelativistic limit Hartree–Fock calculations were also performed for XeF4 at various internuclear distances. The calculated relativistic correction to the total energy of molecule at the Dirac–Fock level is ∼ −5856 eV, whereas the magnetic part of the Breit correction to the electron‐electron interaction is calculated as ∼ 177 eV. The electron correlation effects were included in the nonrelativistic Hartree–Fock calculations using the second‐order Møller‐Plesset (MP2) theory, and the calculated correlation energy for XeF4 is −71 eV. The basis‐set superposition error (BSSE) was estimated by using the counterpoise method for Xe and F. The inclusion of both the relativistic and electron correlation effects in the calculated total energies of F, Xe, and XeF4 predicts the Xe—F bond length and dissociation energy of XeF4 as 1.952 Å and 5.59 eV, respectively, which are in excellent agreement with the experimental values of 1.953 Å and 5.69 eV, respectively, for XeF4. The contribution of the electron correlation and relativistic effects to the dissociation energy of XeF4 is 8.11 and 0.05 eV, respectively. The Breit interaction, however, contributes only 0.02 eV to the dissociation energy of XeF4. Electron correlation is most significant for the prediction of an accurate value of dissociation energy, whereas relativistic effects are very important for the prediction of spin‐orbital splitting as well as the energies of the orbitals, especially the inner orbitals of XeF4. © 1995 John Wiley & Sons, Inc.
Effctive nonadiabatic calculations on the ground state of the HD+ molecule
Authors: Kozlowski Pawel M. , Adamowicz Ludwik 
Published: December 2004

AbstractThe nonadiabatic methodology, which is based on an effective elimination of the center‐of‐mass motion rather than explicit separation achieved by a coordinate transformation, is applied to the ground state of the HD+ molecule. The many‐body nonadiabatic wave function is generated in terms of explicitly correlated Gaussian functions. The analytical first and second derivatives of the variational functional with respect to the Gaussian exponents are applied in conjunction with the Newton–Raphson optimization method to find the nonadiabatic energy and the ground–wave function. The numerical results are compared with conventional nonadiabatic calculations. © 1995 John Wiley & Sons, Inc.
Ab initio calculation of stationary points for the ground and the first excited state of HCO
Authors: Bittererová Martina , Lischka Hans , Biskupič Stanislav 
Published: December 2004

AbstractSCF and single‐reference ACPF calculations were performed in order to determine the structure, stability, and harmonic vibrational frequencies of stationary points for the HCO radical in the ground (2A′) and first excited (2A″) states. Very large and flexible basis sets including two f functions on the heavy atoms and two d functions on hydrogen were used. The calculated geometries and vibrational frequencies are in good agreement with available experimental data. The relative stabilities are now also much better balanced compared to previous theoretical results. © 1995 John Wiley & Sons, Inc.
Complete active‐space configuration interaction with optimized orbitals: Application to Li2
Authors: Evangelisti Stefano , Bendazzoli Gian Luigi , Gagliardi Laura 
Published: December 2004

AbstractWe performed CAS–CI calculations on Li2 using a set of molecular orbitals (MO) optimized with a procedure that, in the case of highly symmetric molecules, permits extraction of a small set of MO out of a large set of atomic orbitals (AO). The dimension of the CAS–CI space was of about 12 million symmetry‐adapted determinants. We determined some spectroscopic constants of Li2 with three different atomic basis sets of increasing quality. The values obtained with the largest atomic basis set are very close to the experimental results. © 1995 John Wiley & Sons, Inc.
The QDPT CI approach for excitation and ionization spectra: A test on the CO molecule
Authors: Lisini A. , Decleva P. 
Published: December 2004

AbstractA detailed analysis of the performance of the QDPT CI method, which is based on the application of quasi‐degenerate perturbation theory (QDPT) within the configuration interaction (CI) approach, is presented by comparing the QDPT CI results and those obtained from the diagonalization of the perturbative space. Calculations of core and valence excitation and ionization spectra of the CO molecule, which is a strongly correlated system, are carried out using a DZ basis set and the accuracy of the eigenvalues and eigenfunctions is checked through the comparison of excitation and ionization energies and intensities. Excellent agreement is obtained for all values, indicating the computational advantages of QDPT CI which is able to explore wide energy ranges without requiring the diagonalization of large spaces. © 1995 John Wiley & Sons, Inc.
On wave‐function correction to Hellmann–Feynman force: Hartree–fock method
Authors: Kryachko Eugene S. 
Published: December 2004

AbstractThe formula for the wave‐function correction to the Hellmann–Feynman force provided by truncation of a basis set of orbitals centered at nuclei is reexamined. Correct application of a projector technique results in the validity of the Hellmann–Feynman theorem for finite basis sets. © 1995 John Wiley & Sons, Inc.
Why N2O2 is cis while (CHO)2 is trans: MO and VBstudies
Authors: Mo Yirong , Zhang Qianer 
Published: December 2004

AbstractThe nonempirical valence‐bond method as well as the molecular orbital method are applied to investigate the structures of N2O2 and (CHO)2. Results show that in either molecule the σ‐component tends toward a trans conformation, whereas, the π‐component tends toward a cis conformation. Moreover, even if there are some long‐range bonding overlaps in the cis structure, the bonding energy cannot counteract the increased Coulombic repulsive energy compared with the trans structure. In other words, for a cis conformation, there is a competition between the Coulombic destabilization and the π electronic stabilization. The latter is more preferable to a cis conformation of N2O2, while the Coulombic repulsive interaction should be responsible for the trans conformation of (CHO)2. The nonempirical vB calculations show that the π delocalization energy in N2O2 is negligible, while the value in (CHO)2 is about 4.5 kcal/mol. © 1995 John Wiley & Sons, Inc.
Theoretical study on the photodecarboxylation reaction of methacrylic acid in the gas phase
Authors: Fang Wei‐Hai , You Xiao‐Zeng 
Published: December 2004

AbstractThe photochemical decarboxylation mechanism of methacrylic acid near 249 nm was investigated with the unrestricted Hartree–Fock method. Our investigation shows that the methacrylic acid molecules obtained by photoexcitation are likely to undergo unimolecular decarboxylation either from its lowest 1nπ* state or, following internal conversion, from the ground state. These results support the photodecarboxylation mechanism proposed by Rosenfeld and Weiner. © 1995 John Wiley & Sons, Inc.
Spectral density distribution of an N‐electron Hamiltonian in a finite‐dimensional and spin‐adapted model space
Authors: Rajadell F. , Planelles J. , Karwowski J. , Mas V. 
Published: December 2004

AbstractExpressions for moments of spectral density distributions of a many‐electron Hamiltonian defined in a finite‐dimensional, antisymmetric, and spin‐adapted model space (as, e.g., a full configuration interaction space) are derived. The moments are expressed in terms of combinations of two‐electron integrals corresponding to a symmetric (a two‐electron singlet) and antisymmetric (two‐electron triplet) two‐electron wave functions. A diagrammatic approach based on Hugenholtz‐type diagrams and leading to a simple and universal classification scheme of the terms appearing in the expression for a specific moment is proposed. © 1995 John Wiley & Sons, Inc.
Near‐Dirac–Hartree–Fock results for first‐row atoms calculated with GTO basis sets
Authors: Datta Sambhu N. 
Published: December 2004

AbstractRelativistic basis sets for first‐row atoms have been constructed by using the near‐Hartree–Fock (nonrelativistic) eigenvectors calculated by Partridge. These bases generate results of near‐Dirac–Hartree–Fock quality. Relativistic total and orbital energies, relativistic corrections to the total energy, and magnetic interaction energies for the first‐row atoms have been presented. The smallest Gaussian expansions (13s8 p expansions) yield Dirac–Hartree–Fock total energies accurate through six significant digits, while the largest expansions (18s13p expansions) give these energies accurate through seven significant digits. These results are more accurate than some of the results reported earlier, particularly for the open‐shell atoms, indicating that the basis employed is reasonably economical for relativistic calculations. © 1995 John Wiley & Sons, Inc.
Method of computer algebraic calculation of the matrix elements in the second quantization language
Authors: Gotoh Masashi , Mori Kazuhide , Itoh Reikichi 
Published: December 2004

AbstractAn automated method by the algebraic programming language REDUCE3 for specifying the matrix elements expressed in second quantization language is presented and then applied to the case of the matrix elements in the TDHF theory. This program works in a very straightforward way by commuting the electron creation and annihilation operators (a† and a) until these operators have completely vanished from the expression of the matrix element under the appropriate elimination conditions. An improved method using singlet generators of unitary transformations in the place of the electron creation and annihilation operators is also presented. This improvement reduces the time and memory required for the calculation. These methods will make programming in the field of quantum chemistry much easier. © 1995 John Wiley & Sons, Inc.
Electronic structures of YBa2Cu3OY doped by La
Authors: Li Ming , Fu Wentao 
Published: December 2004

AbstractBased on the EHMO approach, the band structures for the YBaCuO superconductors doped by La were calculated. The influence of the partial substitutions of La for Y and Ba in YBa2CU3Oy on its electronic structures was investigated. The results demonstrate that the La doping at the Ba site has a great effect on the electronic structures of the YBaCuO superconductors, whereas the change in the band structures caused by the La doping at the Y site is very small. The increase in the oxygen content caused by the La doping results in an increase in the densities of states at Ef, N(Ef), for La1+x Ba2−xCu3Oy, but the increase in N(Ef) cannot compensate the decrease caused by the La doping at the Ba site. In addition, the 2D CuO planes are much more sensitive to the change in N(Ef) than are the 1D CuO ribbons, which implies an important role of the 2D Cu0 planes in the YBaCuO superconducting system, regardless of whether La substitutes for Y or for Ba. © 1995 John Wiley & Sons, Inc.
Local‐scaling transformation version of density functional theory
Authors: Ludeña Eduardo V. , López‐boada Roberto , Maldonado Jorge E. , Valderrama Elmer , Kryachko Eugene S. , Koga Toshikatsu , Hinze Juergen 
Published: December 2004

AbstractThe local‐scaling transformation version of density functional theory (LS‐DFT) is reviewed. It is shown that in the context of LS‐DFT it is possible to construct N‐representable energy density functionals and that the theory provides systematic ways for calculating strict upper bounds to the exact energies. The importance of the concept of “orbit” in LS‐DFT is indicated and several approaches leading to intraorbit and interorbit optimization are discussed. Results of the application of these optimization procedures to the determination of upper bounds for the ground‐state energy of the beryllium atom are given. Also, numerical results are reported on the use of local scaling transformations for the direct solution of the Kohn‐Sham equations via the density‐constrained minimization of the kinetic energy of a noninteracting system. © 1995 John Wiley & Sons, Inc.
On the relation between electronic and nuclear vibrations via the response matrix derived from semiempirical density functional‐based sensitivity analysis
Authors: Janssens Geert O. A. , Baekelandt Bart G. , Toufar Helge , Mortier Wilfried J. , Schoonheydt Robert A. 
Published: December 2004

AbstractEnergetic and physical aspects of the intuitive (mapping) relations between independent (normal) charge polarization patterns and nuclear vibration modes are derived within the atoms‐in‐molecules (AIM) electronegativity equalization method (EEM) formulation of the charge sensitivity analysis (CSA). The concepts are demonstrated with calculations on homologous series of small organic molecules. © 1995 John Wiley & Sons, Inc.
Density functional theory for excited states
Authors: Theophilou Andreas K. , Gidopoulos Nikitas I. 
Published: December 2004

AbstractIn this article, we justify the use of standard Kohn‐Sham (KS) band structure theory for the calculation of the low‐energy spectrum of metals and the density of states. For the higher spectrum, one can start the KS excited‐state calculations by using as the first‐order approximation the spin orbitals of the ground state. We next deal with the problem of degenerate states by using the subspace theory minimum principle. © 1995 John Wiley & Sons, Inc.
Chemical reactivity concepts in charge sensitivity analysis
Authors: Nalewajski Roman F. 
Published: December 2004

AbstractRecent reactivity concepts formulated within charge analysis (CSA) are outlined. The charge stability criteria of equilibrium states in open and closed systems are conveniently characterized in terms of the condensed reactant hardness quantities of reactants; their implications for catatytic systems are examined. A use of characteristics associated with selected collective charge displacement modes, including the populational normal modes and minimum‐energy coordinates, as diagnostic tools in the theory of chemical reactivity is proposed. The importance of the mapping relations between modes defined in the electron population and nuclear position spaces, respectively, as the unifying concept linking the conjugate charge and geometry displacements, is commented upon. Recent results for model catalytic clusters are used to illustrate some of the concepts introduced. Finally, the relevant contributions to the quadratic interaction energy between reactants are reexamined and expressed in terms of relevant charge sensitivities. © 1995 John Wiley & Sons, Inc.
Information entropies of many‐electron systems
Authors: Yáñez R. J. , Angulo J. C. , Dehesa J. S. 
Published: December 2004

AbstractThe Boltzmann–Shannon (BS) information entropy Sρ = ∫ ρ(r)log ρ(r)dr measures the spread or extent of the one‐electron density ρ(r), which is the basic variable of the density function theory of the many electron systems. This quantity cannot be analytically computed, not even for simple quantum mechanical systems such as, e.g., the harmonic oscillator (HO) and the hydrogen atom (HA) in arbitrary excited states. Here, we first review (i) the present knowledge and open problems in the analytical determination of the BS entropies for the HO and HA systems in both position and momentum spaces and (ii) the known rigorous lower and upper bounds to the position and momentum BS entropies of many‐electron systems in terms of the radial expectation values in the corresponding space. Then, we find general inequalities which relate the BS entropies and various density functionals. Particular cases of these results are rigorous relationships of the BS entropies and some relevant density functionals (e.g., the Thomas–Fermi kinetic energy, the Dirac–Slater exchange energy, the average electron density) for finite many‐electron systems. © 1995 John Wiley & Sons, Inc.
A local one‐electron operator for the generalized‐overlap amplitudes
Authors: Day Orville W. 
Published: December 2004

AbstractAn approach to the N‐electron behavior is presented which emphasizes the dynamics of an individual electron. The generalized overlap amplitudes (GOAS), although formally defined by an integration over the coordinates of N − 1 electrons, are, instead, resolved as a column vector, eigenfunction to a local one‐electron differential operator. These amplitudes have no restrictions of linear independence between them, but each satisfies the one‐electron boundary conditions at the nuclei and at large distances. The one‐electron (or charge) density is the sum of the squares of the elements of the column. The energy density, a constant times the one‐electron density, maintains this one‐to‐one relationship throughout modifications in total number of electrons or external potential, although the constant of proportionality, the total energy of the system, may change in the process. Indistinguishability of electrons and antisymmetry is always observed by the dynamics of each electron. A numerical example, the ground state of helium, is presented. © 1995 John Wiley & Sons, Inc.
Theoretical studies of organonickel compounds. I. A density functional and ab initio HF study
Authors: Tobisch Sven , Boegel Horst 
Published: December 2004

AbstractThe π‐allylic organonickel compounds are considered to be key structures in the catalytic reactions of butadiene. Bis(η3‐allyl)nickel, bis(η3‐methallyl)nickel, and the syn–crotyl–cyclooctadiene–nickel cation have been calculated with DZ and TZ basis sets in all‐electron and pseudopotential (ECP) Hartree–Fock (HF) methods and compared with experimental structures. In the second part, we report a systematic investigation of these compounds by density functional theory (DFT). The DFT‐optimized structures are generally in better agreement with experimental data than are the HF results. © 1995 John Wiley & Sons, Inc.
Use of charge sensitivity analysis in diagnosing chemisorption clusters: Minimum‐energy coordinate and Fukui function study of model toluene–[V2O5] systems
Authors: Nalewajski Roman F. , Michalak Artur 
Published: December 2004

AbstractCharge sensitivity analysis (CSA) is carried out for model toluene–vanadium pentoxide chemisorption complexes involving the two‐pyramidal model of the active site on the (010)—V2O5 surface. Maps of the electrostatic potential around the adsorbate and the substrate cluster are used to rationalize energetical preferences of alternative perpendicular and parallel arrangements of the toluene ring relative to the pyramid bases, known from previous SCF MO studies. The minimum‐energy coordinates (MEC) in the electron population space are determined from the CSA semiempirical, finite difference atomic hardness matrix for the actual SCF MO charges in the chemisorption clusters. They represent collective charge displacements which minimize the system energy per unit change in the oxidation state of a specified atom, thus providing a convenient diagnostic tool for testing the alternative charge rearrangements and range of perturbations due to the chemisorption bond or changes in the cluster environment. The MEC relaxed hardnesses diagnose mode stabilities and together with the MEC topologies identify the most probable locations of the adsorbate activation. Finally, the atomic Fukui function indices are used to explore trends in the distribution of the external charge transfer due to the system environment. © 1995 John Wiley & Sons, Inc.
Circumventing the matrix dependent inelastic mean free path in XPS
Authors: Hirokawa Kichinosuke , Danzaki Yuetsu 
Published: December 2004

AbstractThe third partner effect, the so‐called matrix effect, on the inelastic mean free path (IMFP) of electrons affects quantification in XPS of compounds. Experiments on coprecipitate systems involving Ni, Cu, Fe and Mg hydroxides and Ti, Zr, Fe and Mg hydroxides show that the use of neighbouring spectral lines allows this matrix effect (containing errors for sample preparation etc.) to be ignored while retaining a quantification linearity of ∼20%.
XPS mapping technique for the identification of adhesion loss mechanisms
Authors: Haack L. P. , DeBolt M. A. , Kaberline S. L. , Devries J. E. , Dickie R. A. 
Published: December 2004

AbstractAn x‐ray photoelectron spectroscopy (XPS) mapping technique was developed to define spatially the interfacial chemistry of adhesive—adherend debonding. The technique was used to identify mechanisms of corrosion‐induced bond failure for an epoxy adhesive applied to electrogalvanized steel. The specimens studied were lap‐shear bonds exposed simultaneously to a static load and a corrosive environment. The bond failure surfaces were examined after testing. X‐ray photoelectron spectroscopy elemental maps were generated over the entire area (∼ 12.5 mm × 25.0 mm) of the bond failure on both corresponding surfaces at a spatial resolution of 0.4 mm × 0.8 mm. The mapping was accomplished using a fixed small‐spot‐size source in conjuction with computer‐controlled sample stage movement. The XPS elemental maps, and in one case a functional group map, were generated for the constituents of the adhesive (C, O, Si), the adherend (Zn, O) and the aggressive environment (Na, Cl, O, carbonate). The raw XPS intensity data were converted into units of at.% and displayed, using a bilinear interpolation scheme, as three‐dimensional chemical images with a pseudo‐color scale representing variations in elemental surface composition. The images provided detailed evidence for specific sites of anodic and cathodic corrosion processes, and facilitated identification of the locus of adhesive failure.