bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical effects and surface properties: The nature of an adsorbed complex
Authors: Re Giuseppe Del , Peluso Andrea 
Published: January 2005

AbstractThe general Born–Oppenheimer Hamiltonian of an adsorbate is expressed with reference to an AO basis by means of the second quantization technique, and the part representing the in situ adcomplex (admolecule possibly involving adsorption site atoms) is decomposed so as to show how contributions of different effects can be separated. A basic reference Hamiltonian of the adcomplex is defined, and the suggestion is made that it essentially represents a molecular system susceptible of treatment in terms of ordinary localized bonds. This suggestion is shown to be valid for one thing in the highly unsaturated surface complex FeCO (compared with Fe5CO), provided maximum‐localization hybrids are used as elements of the AO basis. The example treated has also been used to show how two kinds of effects can be introduced and discussed: inductive effects, which appear to result from hybridization and from feedback compensations to charge shifts, and charge transfer between the adcomplex and the surface. The proposed local (chemical) description of an adcomplex appears to be an extremely useful tool for describing such complex adsorbates as those associated with Fischer‐Tropsch catalysts. © 1994 John Wiley & Sons, Inc.
Quadrupole and octupole Cauchy moments of the atoms through argon
Authors: Bartolotti Libero J. , Ortiz Luisa , Xie Qingshan 
Published: January 2005

AbstractQuadrupole and octupole Cauchy moments of the atoms through argon are calculated using the hydrodynamic formulation of time‐dependent Kohn–Sham theory. The exchange‐correlation energy density functional is approximated by a gradient expansion for atoms that has an explicit dependence upon the number of electrons. The first‐order corrections to the Kohn–Sham amplitudes and phases are found by seeking variational solutions of the derived sequential set of functionals. The trial functions employed contain both linear and nonlinear variational parameters and are thus flexible enough to provide rapid convergence to the multipole polarizabilities. The resulting Cauchy moments provide information that allows the calculation of various properties that result from the linear interaction of atoms with a time‐varying electric field. © 1994 John Wiley & Sons, Inc.
Structure of the ammonia dimer studied by density functional theory
Authors: Zhu Tianhai , Yang Weitao 
Published: January 2005

AbstractSelf‐consistent Kohn–Sham density functional calculations have been carried out to study the structure of the ammonia dimer. The local‐density approximation yields unusually large binding energy and short internitrogen distance compared with the experimental and more accurate theoretical data. The results from the Becke–Perdew gradient‐corrected functionals are generally in good agreement with those at the SCF MP2 level when the geometry is fully optimized with various large basis sets. With our best estimation, the staggered quasi‐linear structure (Cs) is 0.6 kcal/mol lower in energy than the symmetric cyclic one (C2h). The hydrogen‐bonded N—H bond in the staggered quasi‐linear structure is found to be 0.008 Å longer than the N—H bond in ammonia. In our calculations, we could not find the minima on the energy surface corresponding to the two asymmetric cyclic structures suggested by microwave spectra and coupled pair functional calculations. © 1994 John Wiley & Sons, Inc.
Feynman path integral representation for many‐fermion interacting systems
Authors: Calamante F. , Bochicchio R. C. , Grinberg H. 
Published: January 2005

AbstractA many‐fermion interacting system is investigated within the scenario of the Feynman path integral representation of quantum mechanics. Short‐time propagator algorithms and a basis set, closely related to the coherent states, are used to obtain the many‐body analytic propagator. A second‐quantized Hamiltonian involving a restricted set of two‐body interactions and the whole set of Coulomb interactions are separately and shown to lead to an exact and an approximate propagator, respectively. In the latter case, use of a grand canonical ensemble allows the grand partition function and the density operator matrix to be readily obtained. No further approximations are required in the calculation of the trace of the evolution operator involved in the evaluation of statistical expectation values. © 1994 John Wiley & Sons, Inc.
Brueckner coupled cluster response functions
Authors: Koch Henrik , Kobayashi Rika , Jørgensen Poul 
Published: January 2005

AbstractA derivation of the linear response function for the Brueckner coupled cluster method is presented that enables the calculation of second‐order molecular properties such as frequency‐dependent polarizabilities. By using the Brueckner orbital variant of coupled cluster theory, the spurious pole structure inherent in the standard coupled cluster approach with orbital relaxation is avoided. © 1994 John Wiley & Sons, Inc.
A new single‐center method to compute molecular integrals of quantum chemistry in slater‐type orbital basis of functions
Authors: Bouferguene A. , Rinaldi D. 
Published: January 2005

AbstractThe present work is dedicated to the introduction of a new single‐center expansion method derived from the Barnett and Coulson approach leading to reliable numerical algorithms. The basic concept lies in the use of the integral representations of the modified Bessel functions Iλ+1/2 and Kλ+1/2, rather than employing their closed analytical expressions that are known to involve large numbers that usually make the numerical calculation worthless. It is applied to two‐center overlap and Coulomb integrals as well as to three‐center nuclear attraction integrals useful in density functional theory. © 1994 John Wiley & Sons, Inc.
Quasi‐Spin and the pseudo‐orthogonal group in the hubbard model
Authors: Gould M. D. , Paldus J. , čížek J. 
Published: January 2005

AbstractIn this article, we demonstrate a complementarity between the quasi‐spin SU(2) algebra of the Hubbard model and the pseudo‐orthogonal group O(m,m), where n = 2m is the number of lattice sites. It is shown that all N‐electron states for the one‐dimensional Hubbard model, corresponding to given values of spin and quasi‐spin, give rise to an irreducible representation of O(m,m). Moreover, the cyclic group Cn symmetry of the Hamiltonian is investigated and the O(m,m) ↓ Cn branching rules are determined with the use of the U(n) q‐dimension formula. © 1994 John Wiley & Sons, Inc.
End (electron nuclear dynamics) with the hydrogen molecule used as a model problem
Authors: Pohl Anna , Taylor Hugh , Calais Jean‐Louis 
Published: January 2005

AbstractThe method of electron nuclear dynamics (END) developed by Öhrn and Deumens has been applied to the coupling of electronic structure and vibrational motion in the hydrogen molecule with the aim of elucidating and illustrating the characteristic features of this method. © 1994 John Wiley & Sons, Inc.
Ab initio CI calculations on benzene with an extended basis set
Authors: Yamamoto Yuichi , Noro Takeshi , Ohno Kimio 
Published: January 2005

AbstractAn extended basis set of triple zeta plus polarization quality is employed to carry out configuration interaction (CI) calculations of the three lowest singlet and triplet excited states of benzene. The CI calculation is carried out by taking into account single and double excitations of π and σ electrons. In the CI, composite natural orbitals (CNOs), which are constructed from the natural orbitals of the ground state of ethylene, are used as virtual orbitals. The aim of using CNOs is to reduce the number of virtual orbitals to be used in constructing configuration‐state functions, thus cutting down CI dimensions without losing reasonable accuracy. The excitation energies resulting from the CI are in fairly good agreement with experiment. The root mean square of the deviation is 0.22 eV for the six calculated energies and the largest disagreement is 0.37 eV for the third singlet excited state. To obtain better excitation energies by an ab initio calculation, it seems likely that we need to take into account more electron correlation than in the present calculation. © 1994 John Wiley & Sons, Inc.
The helium atom in its ground state embedded in strong magnetic fields
Authors: Rivas‐Silva J. F. 
Published: January 2005

AbstractThe helium atom in its ground state, subject to strong magnetic fields, is treated using a variational method. Trial functions consisting of Gaussians with nonlinear parameters variationally optimized are used. The form of these functions is a generalized s‐symmetry‐state properly modified to admit spatial deformation along the direction on which the magnetic field is applied. © 1994 John Wiley & Sons, Inc.
Path integral approach to correlation energy
Authors: Kawabe H. , Nishikawa K. , Aono S. 
Published: January 2005

AbstractThe Feynman path integral method is applied to the many‐electron problem of quantum chemistry. We begin with investigating the partition function of the system in question; then, “a classical path of electron” that corresponds to the Hartree–Fock approximation is obtained by minimizing the thermodynamic potential of the system with respect to the electron coordinate. The next‐order approximation is obtained by evaluating the deviation from this classical path, which is approximately written by an easily integrable Gaussian integral. The result is expected to be the random‐phase approximation. As numerical examples, the hydrogen molecule and butadiene are treated. © 1994 John Wiley & Sons, Inc.
Direct solution of the many‐body Schrödinger equation in the hyperspherical formalism: Formulation of the CFHH–GLF method
Authors: Bian Wensheng , Deng Conghao 
Published: January 2005

AbstractTo accelerate the convergence of the HH expansion, we modified the HH–GLF method, a new simple hyperspherical harmonic method proposed recently by us, into the CFHH–GLF method. Applications of the CFHH–GLF method to the three‐body systems He and e− e− e+ exhibit very fast convergence with number of HH basis sets. With only 36 HH and five GLF, we obtain the ground‐state energy of −2.90371 au for He, compared with the exact value of −2.90372 au, and with only 36 HH and 10 GLF, we obtained the ground‐state energy of ‐0.26188 au for e− e− e+, compared with the exact value of −0.26200 au. We formulate the CFHH–GLF method in this article. © 1994 John Wiley & Sons, Inc.
Incidence of the muffin‐tin approximation on the electronic structure of large clusters calculated by the MS–LSD method: The typical case of C60
Authors: Razafinjanahary H. , Rogemond F. , Chermette H. 
Published: January 2005

AbstractThe MS–LSD method remains a method of interest when rapidity and small computer resources are required; its main drawback is some lack of accuracy, mainly due to the muffin‐tin distribution of the potential. In the case of large clusters or molecules, the use of an empty sphere to fill, in part, the large intersphere region can improve greatly the results. Calculations bearing on C60 has been undertaken to underline this trend, because, on the one hand, the fullerenes exhibit a remarkable possibility to fit a large empty sphere in the center of the cluster and, on the other hand, numerous accurate calculations have already been published, allowing quantitative comparison with our results. Our calculations suggest that in case of added empty sphere the results compare well with the results of more accurate calculations. The calculated electron affinity for C60 and C are in reasonable agreement with experimental values, but the stability of C in gas phase is not found. © 1994 John Wiley & Sons, Inc.
Disordered grown systems: Generation and fractal analysis. Electrodeposition
Authors: Sagués Francesc , López‐tomàs Laura , Mach Jordi , Reigada Ramon , Trigueros Pedro Pablo , Vilaseca Eudald , Claret Josep , Mas Francesc 
Published: January 2005

AbstractThe basic concepts of fractal geometry are reviewed and applied to quasi‐two‐dimensional zinc electrodeposits. Among the different structures developed during zinc electrodeposition, we have identified the open texture (obtained at large zinc sulfate concentration and small applied potential values) as a typical fractal self‐similar structure. © 1994 John Wiley & Sons, Inc.
The interaction of chemical bonds. III. Perturbed strictly localized geminals in LMO basis
Authors: Surján Péter R. 
Published: January 2005

AbstractThe formalism of strictly localized geminals (SLGs) is summarized. It is shown that the SLG wave function serves as an appropriate multiconfigurational reference state that can easily be improved by perturbational, CI‐ or coupled cluster‐type procedures. The possibility of expanding the geminals in the basis set of localized Hartree‐Fock molecular orbitals (LMOs) is discussed. Sample calculations on H4, CH4, H2O, and He…︁He systems are reported. © 1994 John Wiley & Sons, Inc.
Theoretical study of [Li(H2O)n]+ and [K(H2O)n]+ (n = 1−4) complexes
Authors: Wójcik Marek J. , Mains Gilbert J. , Devlin J. Paul 
Published: January 2005

AbstractThe geometries, successive binding energies, vibrational frequencies, and infrared intensities are calculated for the [Li(H2O)n]+ and [K(H2O)n]+ (n = 1−4) complexes. The basis sets used are 6‐31G* and LANL1DZ (Los Alamos ECP+DZ) at the SCF and MP2 levels. There is an agreement for calculated structures and frequencies between the MP2/6‐31G* and MP2/LANL1DZ basis sets, which indicates that the latter can be used for calculations of water complexes with heavier ions. Our results are in a reasonable agreement with available experimental data and facilitate experimental study of these complexes. © 1995 John Wiley & Sons, Inc.
Electronic structure of crystals: Embedded quantum cluster with overlap
Authors: Vail John M. , Rao Bijan K. 
Published: January 2005

AbstractWe consider a crystal as partitioned into a localized molecular cluster (containing a defect or not) and an embedding region. Within the Hartree–Fock formalism, an expression is derived for an effective potential due to the embedding region of crystal. This potential is part of the cluster Fock operator and requires input from a perfect crystal calculation. Special features of the derivative are rigorous inclusion of cluster‐embedding overlap and orthogonality between single‐electron states of the embedding region and the function‐space manifold of the cluster; physically correct normalization of the Fock eigenstates; and a nontrivial total‐energy algorithm. Computational requirements are qualitatively compared with those for an isolated cluster. The method allows for intracluster (and intraembedding) correlation and can be adapted straightforwardly to local density functional approaches. Fundamental aspects of the embedding problem are addressed in a general formulation that is, nevertheless, oriented toward explicit calculations. © 1995 John Wiley & Sons, Inc.
Band structure of solids from clusters SCF potentials
Authors: Nour Safouh , Chermette Henry 
Published: January 2005

AbstractThe possibilities and limits of the molecular orbital theory to deal with the problem of determining electronic structure of solids have been explored. A cluster model based on the charge neutrality in the solid has been used in test calculations on some III–V semiconductors and have given quite satisfactory results. Recommendations are given to widen the field of applications of this procedure. © 1995 John Wiley & Sons, Inc.
Is there any three‐center CBC bond in 1, 5‐C2B3H5 and 1,5‐C2B3H3?
Authors: Kar Tapas , Jug Karl 
Published: January 2005

AbstractLocalized molecular orbitals, two‐ and three‐center bond indices of 1,5‐dicarba‐closo‐pentaborane (5) and 1,5‐dicarba‐closo‐pentaborane (3) and their hydrocarbon analogs bicyclo [1,1,1]‐pentane and [1,1,1] propellane, respectively, have been calculated using a suitable basis set. No previously reported three‐center CBC bond has been found. However, a new three‐center BCB bond has been observed in 1,5‐dicarba‐closo‐pentaborane (5). © 1995 John Wiley & Sons, Inc.
Multiple solutions of the single‐reference coupled‐cluster equations. II. Alternative reference states
Authors: Jankowski K. , Kowalski K. , Jankowski P. 
Published: January 2005

AbstractSingle‐reference coupled‐cluster (SR–CC) methods parametrized with respect to four alternative reference‐state configurations and orbital sets are applied to the simple H4 model system in which the degree of quasi‐degeneracy of the electronic states can be varied in a wide range. Both the ground state and 10 excited states are considered with the aim of numerically studying the attainability and properties of multiple solutions of the system of nonlinear equations for the cluster amplitudes. Comparisons of up to four alternative descriptions of a given state in terms of various solutions of the SR–CC equations are made. It is found that for some excited states different parametrizations yield very close results and that the classification of the solutions into standard and nonstandard ones may not be straightforward. © 1995 John Wiley & Sons, Inc.
Asymmetries and anisotropies in the Compton scattering from the hydrogen molecule
Authors: Roeth M. , Gasser F. , Tavard C. 
Published: January 2005

AbstractThe Compton energy loss spectra of atomic targets exhibits usually a specific asymmetry due to the postcollisional electrostatic interaction between the remaining ion and the ejected electron. This asymmetry, or Compton defect, also exists in the scattering by molecules or solids. The first attempt to describe the Compton defect for the hydrogen molecule is proposed here. The Compton energy loss spectra depends particularly on the relative orientation of the momentum transferred by the incident particle and the molecular axis. A comparison between the respective magnitudes of Compton profiles and Compton defects was one of the aims of this article. The results emphasize the particular interest of a simultaneous interpretation of both symmetrical and antisymmetrical contributions in the study of molecular or solid‐state electronic structures. © 1995 John Wiley & Sons, Inc.
Eigenstates of double wells at varying well depths
Authors: Pathak R. K. , Bhattacharyya K. 
Published: January 2005

AbstractA recipe for the accurate calculation of eigenstates of quartic double‐well oscillators is presented. The behavior of eigenenergies as a function of the coupling strength is also studied. The quality of the semiclassical (WKB) expression for eigenvalues is critically assessed in this context. The analysis also includes a discussion on the possibility of degeneracy in such one‐dimensional systems. © 1995 John Wiley & Sons, Inc.
Nonlinear population analysis from geminal expansion of pair densities
Authors: Ponec Robert , Bochicchio Roberto C. 
Published: January 2005

AbstractThe nonlinear population analysis of pair densities introduced by one of us (R. B.) is reformulated using the geminal expansion of pair densities. The pair density in the geminal basis is idempotent and allows one to describe the bonding patterns as singlet‐and tripletlike contributions while still conserving the statistical nature of the original formalism. The new approach is applied to the analysis of pair densities derived from semiempirical MNDO calculations. The resulting values of pair populations of several simple molecules are discussed. © 1995 John Wiley & Sons, Inc.
Conformational study of halogen‐ and hydrogen‐substituted polythionylphosphazenes using density functional theory method
Authors: Raja A. V. , Lagowski J. B. 
Published: January 2005

AbstractThe structure and conformational stability of polythionylphosphazenes is investigated by modeling single polymer chains with small mimics. The model compounds are composed of repeat units of the corresponding polythionylphosphazenes. Two of the model compounds have hydrogens and two have chlorines as substituents on phosphorus atoms. The substituents on sulfur may be either fluorine or chlorine. Fully geometry‐optimized structures and energies of the stable conformations involving rotations around the PN bond near the sulfur are obtained using the density functional theory method. The structural and conformational analyses indicate that the rotation around the NP bond leads to variations in the bond lengths, the SNP bond angle openings, as well as couplings between dihedral angles in different conformations in all model compounds. In addition, the conformational analysis suggests that the minima on the conformational potential energy surface in these compounds may be located in the vicinity of the following values of the NPNS dihedral angle: ‐50°, 90° (or 60°), 180°, and 240°. It was found that the values of the conformational energy differences range between less than 1 to 5 kcal/mol. A comparison is made between the structural results obtained using the density functional theory and the ab initio molecular orbital theory for the global minimum structures. © 1995 John Wiley & Sons, Inc.
Studies on the mechanism of Mannich reaction involving iminium salt as potential Mannich reagent. III. Furan as pseudo acid component
Authors: Li Yu Min , Xiao He Ming 
Published: January 2005

AbstractStructures, heats of formation, and vibrational eigenvalues have been calculated by semiempirical AM1 quantum mechanical method for the reactants, products, and activated complexes of three Mannich reactions, namely, the reaction between potential Mannich reagent H2N+ = CH2Cl− and furan and the conventional Mannich reactions between ammonia, formaldehyde, and furan in neutral and acidic media. It has been found that the Mannich reaction involving the potential Mannich reagent occurs more quickly than do the conventional Mannich reactions in neutral medium; the Mannich reaction in acidic medium proceeds most quickly. The results have been discussed in terms of the orbital match and static electric interaction between some atoms of reactant complexes. © 1995 John Wiley & Sons, Inc.
Hydrogen‐bonding effects, electrostatic potential, and the antitumor activity of flavone acetic acid and related compounds. I. Ab initio studies on the first stable conformations
Authors: Fang Jian‐Yun , Thomson Colin 
Published: January 2005

AbstractAb initio investigations have been carried out to account for the antitumor activity of flavone acetic acid (FAA) and related compounds. The hydrogen‐bonding conformation was chosen for all the compounds and obtained through a restricted geometry optimization with the 3‐21G basis set. Three key regions in the molecular electrostatic potential isosurfaces [V(r) ∼ −0.015 au] are found to be involved in the activity. Region 1 is the most important. Its existence implies the activity and its size determines the strength of the activity. Region 2 is another factor which can change the strength of the activity. Region 3 corresponds to the hydrogen‐bonding effects which have been analyzed in detail, but its role is still not clear. Finally, basis‐set effects on the molecular electrostatic potential have been briefly discussed. © 1995 John Wiley & Sons, Inc.
Kritische Studien zur volumetrischen Bestimmung von karbonathaltigen Alkalilaugen und von Alkalikarbonaten, sowie über das Verhalten von Phenolphtaleïn und Methylorange als Indikatoren
Authors: Küster F. W. 
Published: January 2005

Abstract1. Von den verschiedenen Methoden, welche für die titrimetrische Bestimmung gemischter Lösungen von Alkalihydroxyden und Alkalikarbonaten vorgeschlagen worden sind, liefert nur die Baryumchloridmethode in der von CL. WINKLER empfohlenen Ausführung (direkte Titration der Lösung samt Niederschlag mit Phenolphtaleïn als Indikator) mit Sicherheit richtige Resultate für das Alkalihydroxyd. Das Gesamtalkali kann durch Titration mit Methylorange als Indikator richtig bestimmt werden.