bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sur une tentative d'unification des théaories quantiques de la cancérisation par les polyacènes. II: Le rôle de la rèagion K dans le processus d'activation metabolique conduisant au cancérogène ultime. Théorie des régions M, L, et BK
Authors: Gayoso Jose , Kimri Said 
Published: January 2005

AbstractThis study is a unified approach to quantum theories of polyacen carcinogenesis. Part II is on the role of the K‐region in metabolic activation process leading to ultimate carcinogen and discusses the M, L, and BK theory. The saturation of the polyacen K‐region, or the transformation into a quinoid one, deactivates the carcinogenic process going through a diol epoxyde, which results in Bay‐region carbocation. K and B regions must be considered as two interdependent parts of the same structural entity, which may be termed the BK‐region. The M, L, and BK theory achieves a complete unification of the Pullman and Jerina and other theories.
Transition structures and energy barriers of pericyclic reactions in the CASSCF approach
Authors: Janoschek Rudolf , Kalcher Josef 
Published: January 2005

AbstractFive energy hypersurfaces of the most examined pericyclic reactions have been investigated by using ab initio SCF, CASSCF, and the semiempirical AM1 methods. The systems are H4, H6, C3H6, C4H4, and C3OH4. Stationary points and their sets of harmonic vibrational frequencies have been calculated by means of analytical gradient techniques in the frameworks of the respective approaches. ZPE corrected energy barriers are based on single‐point calculations including dynamical correlation corrections by CAS‐CI(SD)+DC, CASCEPA, or MP2.
Covalent and ionic contributions to the bonding of atomic and molecular adsorbates on metal surfaces: A cluster model approach
Authors: Pacchioni G. , Bagus P. S. , Philpott M. R. , Nelin C. J. 
Published: January 2005

AbstractThe molecular cluster model approach for the description of processes at surfaces is presented. It involves using finite clusters that contain surface atoms interacting with atomic or molecular adsorbates. Accurate ab initio wave functions can be obtained for the clusters, and, thus, this makes it possible to describe the bonding in terms that are familiar for molecular systems. The adsorbate‐substrate interaction can be analyzed by new techniques developed to characterize the bonding as covalent or ionic. This is shown for F on Ag(111) and O and CO on Cu(100) systems. The measures of adsorbate ionicity are (a) the expectation value of a projection operator giving an indication of the number of electrons associated with the adsorbate, (b) the analysis of the dipole moment curve as function of the distance, and (c) the effect of an external electric field on the adsorbate geometry. The consequences of ionic adsorbates on metal surfaces is discussed for two selected topics: adsorption of thiocyanate on Ag electrodes and coadsorption of CO with ionic species.
Point group symmetry and cartesian force constant redundancy
Authors: Stanton John F. 
Published: January 2005

AbstractA procedure for identifying redundancy in the Cartesian force constant matrix is described, and a prescription is given for generating the entire matrix of second derivatives from the minimal set of information. A proof is supplied which demonstrates that the number of nonredundant rows corresponding to a symmetry unique atom is necessarily less than three if the atom is invariant with respect to a symmetry operation of the point group other than the identity or inversion. Furthermore, only one row is required if the atom lies on a threefold or higher‐order rotation axis. An application of the procedure to the evaluation of harmonic force constants by numerical differentiation of gradient vectors is briefly described.
The rapid estimate of a gauss integral
Authors: Jiancheng Xuan , Shouping Jiang 
Published: January 2005

AbstractWe propose a fomula that directly gives an estimate of the value of a Gaussian integral through only one multiplication. Using this formula, we may neglect about 60%–80% of integrals in quantum chemical ab initio calculations, without any loss in precision theoretically. Such a large molecule as ATP with 183 STOS using the STO‐2G method has been calculated utilizing this technique, and only 31 CPU hours of VAX 11/730 were spent on integrals.
Band structure and electronic properties of lithium azide (LiN3)
Authors: Seel Max , Barry Kunz A. 
Published: January 2005

AbstractAb initio Hartree–Fock band structure and molecular calculations have been performed to study the electronic structure of LiN3 in a monoclinic C 2/m crystal structure. The total energy, band structure, density of states, and charge densities are computed. The calculated lattice energy (energy to separate the ions infinitely apart) of 8.6 eV agrees very well with 8.45 eV deduced from Madelung and London polarizability energies. The calculated split of the N 1s core bands of 5.0 eV compares favorably with the experimental X‐ray photoelectron value of 4.4 eV. This good agreement is not contributed to crystalline environment effects as proposed in earlier MO studies of N where the best values obtained were 5.1, 5.8, and 6.3 eV, but to the quality of the nitrogen core basis set. The calculated valence density of states supports one of two competing interpretations that peak III observed in the X‐ray photoelectron spectrum arises from contaminations or other extrinsic states.
Collision‐induced emission of O2(b1Σ → a1Δg) in the gas phase
Authors: Fink E. H. , Setzer K. D. , Wildt J. , Ramsay D. A. , Vervloet M. 
Published: January 2005

AbstractIn flow tube studies of the quenching of O2(b1Σ), broad band emission of O2(b):M collision complexes was found to appear under the discrete rotational lines of the 0–0 band of the b1Σ → a1Δg electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision‐induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from low‐resolution measurements of the relative intensities of the b → a and b → X bands as a function of O2 and added gas pressure. They range from ≈10−21 cm3 s−1 for He to ≈4 × 10−19 cm3 s−1 for PCl3 vapor.
Polarization propagator calculation of spectroscopic properties of molecules
Authors: Oddershede Jens , Sabin John R. 
Published: January 2005

AbstractWe propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second‐order polarization propagator approximation (SOPPA) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin‐spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.
A realistic model for curve crossing in diatomic molecules
Authors: Broeckhove J. , Lathouwers L. 
Published: January 2005

AbstractWe present a model system for the study of curve‐crossing situations in diatomic molecules. All model parameters are determined by the potential energy topology. No coupling functions are fitted. The standard approximation schemes (Born–Oppenheimer approximation, adiabatic approximation, and the generator coordinate approximation) are then applied. The result of these numerical experiments suggest that the generator coordinate approximation is able to remove 80%–90% of the nonadiabatic effect on all levels throughout the crossing region.
The exact form of the Pauli potential for the ground state of two‐ and three‐level atoms and ions
Authors: Nagy A. , March N. H. 
Published: January 2005

AbstractThe square root of the electron density satisfies a Schrödinger equation having a correction term, called the Pauli potential, in addition to the Kohn–Sham potential. The Pauli potential is given in exact form for the ground state of two‐ and three‐level atoms and ions (e.g., Be and C). Expressions for the kinetic energy and the one‐body virial are also derived.
Improved quadrature methods for three‐center nuclear attraction integrals with exponential‐type basis functions
Authors: Homeier Herbert H. H. , Otto Steinborn E. 
Published: January 2005

AbstractThe numerical properties of a two‐dimensional integral representation [J. Grotendorst and E.O. Steinborn, Phys. Rev. A 38, 3857 (1988)] of the three‐center nuclear attraction integral with a special class of exponential‐type orbitals (ETO'S), the B functions [E. Filter and E.O. Steinborn, Phys. Rev. A 18, 1 (1978)] are examined. B functions span the space of ETO'S. The commonly occurring ETO'S can be expressed in terms of simple finite sums of B functions. Hence, molecular integrals for other ETO'S, like the more common Slater‐type orbitals, may be found as finite linear combinations of integrals with B functions. The main advantage of B functions is the simplicity of their Fourier transform that makes the derivation of relatively simple general formulas for molecular integrals with the Fourier transform method possible. The integrand of the integral representation mentioned above shows sharp peaks causing, in the case of highly asymmetric charge distributions, slow convergence of the quadrature method used by Grotendorst and Steinborn. New quadrature schemes are presented that use quadrature rules based on Möbius transformations. These rules are well suited for the numerical quadrature of functions that possess a sharp peak at or near a single boundary of integration [H.H.H. Homeier and E.O. Steinborn, J. Comput. Phys., 87, 61 (1990)]. Numerical results are presented that illustrate the fact that convergence of the new quadrature schemes is about a factor two faster in case of highly asymmetric charge distributions.
Maximum overlap symmetry orbitals
Authors: Zhan Chang‐Guo , Zheng Fang 
Published: January 2005

AbstractBased on the principle of maximum overlap, a new simple method is suggested for constructing the symmetry orbitals of arbitrary molecules and the delocalized molecular orbitals of molecules that do not involve the rings with an odd number of atoms. All these orbitals, called “maximum overlap symmetry orbitals,” are determined by an extended maximum overlap criterion and form the bases for the irreducible representations of the molecular point symmetry group. The theoretical analysis and the numerical results show that the obtained molecular orbitals are close to those obtained from the customary LCAO method, and calculation by the proposed method requires less computing time than does the LCAO method, thus illustrating a fact that the method is not only a reasonable approximation of the LCAO method, but simpler and feasible in large molecular systems.
Construction of orthogonal subspaces
Authors: Banerjee Ajit 
Published: January 2005

AbstractAn orthogonalization procedure is presented that allows construction of at least (n−m) vectors orthogonal to {Xj}, j equals; 1, m, by linear combinations solely among {ηi}, i equals; 1, n, n>m, and 〈Xj/ηi〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).
A density functional for the correlation energy, deduced in the framework of the correlation factor approach
Authors: Moscardó Federico , San‐Fabián Emilio 
Published: January 2005

AbstractAn approximate density functional is deduced from a wave function within the correlation factor method. The new functional does not include terms depending on the gradient of the density, but shows the simplicity of local density functionals without spin polarization. However, it includes correctly the inhomogeneity effects and, also, the nonlocal nature of an electronic system. The approach adopted here stresses the goodness of the expression taken by Colle and Salvetti for building a correlation factor and, at the same time, allows us to gain light on the nature of the deficiencies of those functionals obtained, up to now, from the perspective of the Hohenberg and Kohn theorem.
Quantum rigid dipole in a permanent electric field. I. Rigorous treatment
Authors: Kryachko Eugene S. , Yanovitskii Oleg E. 
Published: January 2005

AbstractA behavior of a quantum rigid and pointlike dipole in a permanent electric field is under study. A dependence of a number of librational energy levels on the strength of the electric field is investigated on the basis of some rigorous results for the appropriate normal Jacobian matrices.
Atoms and electron‐pair bonds in a molecule: An approach within the context of extended geminal models
Authors: Røeggen I. 
Published: January 2005

AbstractWithin the framework of extended geminal models, the meaning of the electron‐pair bond concept is substantiated. If there exist two‐centered electron‐pair bonds in a molecule, it is demonstrated that the molecule can be partitioned into neutral fragments. The total electronic energy can then be written as a sum of intra‐ and interfragment energies. If the electron‐pair bonds are only on the two‐center type, the advocated procedure leads to the definition of an atom in a molecule. As test cases, the bonding in H2 and HF, the difference in equilibrium geometries of H2O and H2S, and the origin of the ethane rotational barrier are analyzed.
Quantum localization over a potential barrier
Authors: Atabek O. , Lefebvre R. , Sucre M. Garcia , Gomez‐Llorente J. , Taylor H. 
Published: January 2005

AbstractThe ability of a harmonic barrier to support resonances is examined. Stabilization graphs calculated from box quantization have the features expected for resonances at an energy equal to the barrier maximum. The search for a wave packet of maximum lifetime leads also to this energy. These findings agree with the energies associated with the poles of the S matrix.
First‐Order geometrical response equations for state‐averaged multiconfigurational self‐consistent field (SA‐MCSCF) wave functions
Authors: Bak Keld Lars , Boatz Jerry , Simons Jack 
Published: January 2005

AbstractThe first‐order geometrical response equations for a state‐averaged multiconfigurational self‐consistent field (SA‐MCSCF) calculation are derived. This derivation is carried through from first principles to final working equations suited for computer implementation. The final equations are expressed such that the energies and wave functions must be known only for the internal SA‐MCSCF states. In the derivation, the special but important case where two or more internal states have equal weighting factors is treated in a manner fully consistent with all other cases. Except for introducing extra equations that are straightforward to solve, the case where two or more internal states have equal weighting factors introduces no new complications.
Ab initio MRD–CI calculations on cubane (neutral, carbocation, carboanion) and dissociation of nitrocubanes based on localized orbitals
Authors: Chapman Douglas A. , Kaufman Joyce J. , Buenker Robert J. 
Published: January 2005

AbstractAb initio MRD–CI calculations based on localized orbitals were carried out for cubane (neutral, carbocation, carboanion) both in our customary MODPOT basis set and in an all‐electron 4–31G basis set. The calculated MRD–CI charge distributions on C1 (the skeletal atom from which the H− or H+ was removed) (ab initio MODPOT neutral 4.221, carbocation 3.796, carboanion 4.282; all‐electron 4–31G neutral 6.171, carbocation 5.717, carboanion 6.078) indicate that the + or ‐ charge does not remain localized on C1 but redistributes itself. This has significant implications for preparative reactions of energetically substituted cubanes. The MRD–CI population analyses differ somewhat from the SCF population analyses, especially in the calculated total overlap populations. To investigate this effect on electrostatic molecular potential contour (EMPC) maps generated from SCF or MRD–CI wave functions, we wrote additional routines to calculate EMPC maps from MRD–CI wave functions. The EMPC maps generated from SCF or MRD–CI wave functions are different if the molecule needs an MRD–CI multideterminant wave function to describe it adequately. The EMPC map is a one‐electron property. One‐electron properties are derived from the 1‐matrix. The 1‐matrix is different for SCF or MRD–CI wave functions. Thus, all the one‐electron properties (EMPC maps, population analyses, bond deviation indices, etc.) are different when calculated from SCF or MRD–CI wave functions if MRD–CI wave functions are necessary to describe a system properly. We calculate these one‐electron properties from the 1‐matrix from the final natural orbitals. Our preliminary calculations for the dissociation pathway indicate it takes more energy to dissociate a bond in 1‐nitrocubane than in octanitrocubane. Even in their ground electronic states at equilibrium geometry, both 1‐nitrocubane and octanitrocubane require MRD–CI wave functions to describe them properly. The c2 of the single determinant SCF wave function is only 0.8401 for 1‐nitrocubane and 0.8300 for octanitrocubane. There are contributions from skeletal excitations as there are for cubane itself as well as excitations involving the nitrogroup. As the bond in nitrocubane is dissociated to 8.00 bohrs, the c2 of the SCF contribution drops to only 0.4606 (1‐nitrocubane) and 0.4445 (octanitrocubane). At this C1N1 intermolecular distance, the largest excitations are in the C1N1 bond: (C1N1)2 → (C1N1*)2, (C1N1) → (C1N1*). We also calculated the first electronically excited state for the dissociation pathway for selected points for both 1‐nitrocubane and octanitrocubane.
Calculating energy spectrum of one‐dimensional quantum systems with rational potential P(X)/Q(X)
Authors: Rivas‐Silva J. F. , Campoy G. , Palma A. 
Published: January 2005

AbstractThe solution of the Schrödinger equation for rational potentials is given using an extension of a previous numerical method. The comparison with other methods shows that ours is a good alternative to those that use the Taylor series approximation of wave function. We illustrate the algorithm considering the Mitra and the Newton–Thomas potentials as examples.
The electronic structure of parallel β‐pleated sheets in proteins: An ab initio computation including electron correlation
Authors: Suhai S. 
Published: January 2005

AbstractThe electronic structure of a 2D polyglycine network with a pleated sheet structure has been computed at the Hartree–Fock level and by including electron correlation effects within the second order of many‐body perturbation theory (electron polaron model). The influence of the size of the atomic basis set and of the extension of the virtual space has been investigated both for single‐ and many‐particle properties. Comparison with the energy of the corresponding single chains showed that interchain interactions (mainly hydrogen bonding) provide an extra stabilization for the 2D network by 7.4 and 10 kcal/mole per glycine residue at the Hartree–Fock and correlated levels, respectively. The energy dispersions are rather anisotropic for all bands whose widths are about 0.5–1 eV along the polypeptide backbones and 0.1–0.2 eV in the perpendicular direction (hydrogen bonds). The HF value of the fundamental energy gap is reduced by 4 eV to 9.2 eV for electron polarons. The wave functions and interaction integrals obtained can be used to calculate further optical and lattice vibrational properties.
Ab initio SCF calculations on [V10O28]6−: A benchmark for the classical calculation and processing of molecular integrals on large Gaussian basis sets
Authors: Rohmer Marie‐Madeleine , Ernenwein René , Ulmschneider Michel , Wiest Roland , Benard Marc 
Published: January 2005

AbstractA vector efficient implementation of the McMurchie and Davidson algorithm for the calculation of one‐ and two‐electron molecular integrals is presented, as available in the Cray version of the ASTERIX program system. The implementation and performance of a vector‐oriented strategy for the generation and processing of the P supermatrix is also discussed. This program system has been applied to the ab initio SCF computation of the ground‐state wave function for the [V10O28]6− ion, with a basis set of triple‐zeta quality for the valence shell of oxygen generating 1404 GTOS and 574 CGTOS for the complete system. The performance and the bottlenecks of the integral calculation are discussed as a function of the integral classes. Two‐dimensional maps of the electrostatic potential are presented for this molecule and compared to experimental information about proton fixation.
A contracted bromine basis set for use in calculation of molecular energies
Authors: Curtiss L. A. , Binning R. C. 
Published: January 2005

AbstractA contracted [9s6p2d] basis set derived from Dunning's (14s11p5d) primitive Gaussian set for bromine has been used in ab initio molecular orbital calculations of the dissociation energies of HBr, CH3Br, and Br2, the ionization potentials of Br and HBr, and the electron affinity of Br. The calculated energies are within 0.1 eV of the experimental values. This is similar to the accuracy obtained in a previous study, also using a contracted [9s6p2d] basis set, of the dissociation and ionization energies of the GeHn, AsHn, and SeHn hydrides.
Ab initio relativistic effective potentials with spin‐orbit operators. VI. Fr through Pu
Authors: Ermler W. C. , Ross R. B. , Christiansen P. A. 
Published: January 2005

AbstractAb initio averaged relativistic effective core potentials (AREP), spin‐orbit (SO) operators, and valence basis sets are reported for the elements Fr through Pu in the form of expansions in Gaussian‐type functions. Gaussian basis sets with expansion coefficients for the low‐energy states of each atom are given. Atomic orbital energies calculated under the j–j coupling scheme within the self‐consistent field approximation and employing the AREP'S in their unaveraged form (REP'S) agree to within 10% of orbital energies due to numerical all‐electron Dirac–Fock calculations. The accuracy of the AREP'S and so operators is also shown to be good through comparisons of calculated so splitting energies with all‐electron Dirac–Fock results.
The COLUMBUS Standard Integral File Structure: A proposed interchange format
Authors: Shepard Ron 
Published: January 2005

AbstractThe integral file structure used in the COLUMBUS Program System is described. This file structure is proposed for use as an interchange format for the exchange of information between various electronic structure codes. Access to the integral and density matrix arrays stored in the file structure is simplified by a supporting subroutine library. This library is portable across various computers and is readily available to programmers from the COLUMBUS distribution files. This library provides for the efficient processing of individual records, including the use of asynchronous I/O and the vectorized processing of packed orbital labels. The individual arrays are identified in a self‐defining and extensible manner, allowing for the addition of new integral types as demanded by the application. The format of the individual records is also self‐defining, allowing for the use of various packing and data compression methods within each record without burdening the calling program with unnecessary complications.