bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simplified derivation of a one‐range addition theorem of the Yukawa potential
Authors: Homeier H. H. H. , Weniger E. J. , Steinborn E. O. 
Published: January 2005

AbstractThe one‐range addition theorem [J. Fernández Rico, R. López, and G. Ramírez, Int. J. Quantum Chem. 34, 121 (1988)] for the Yukawa potential is rederived in a very simple manner using weakly convergent expansions [E. J. Weniger, J. Math. Phys. 26, 276 (1985)] of plane waves in the Fourier representation. It is discussed in which sense the addition theorem converges. The relation to Sturmian expansions of Coulomb Green functions is pointed out. © 1992 John Wiley & Sons, Inc.
Simulated annealing to locate various stationary points in semiempirical methods
Authors: Bockisch F. , Liotard D. , Rayez J.‐C. , Duguay B. 
Published: January 2005

AbstractIn this work, an algorithm was developed to study the potential energy surfaces in the coordinate spaces of molecules by a nonlocal way, in contrast to classic energy minimizers as the BFGS or the DFP method. This algorithm, based on the specificities of semiempirical methods, mixes simulated annealing and local searches to reduce computation costs. By this technique, the global energy minimum can be localized. Moreover, local minima that are close in energy to the global minimum are also obtained. If the search is not only for minima but for all stationary points (minima, saddle points…), then the energy is replaced by the gradient norm, which reaches its minimum values at stationary points. The annealing process is stopped before having accurately reached the global minimum and generates a list of geometries whose energies (respectively, whose gradients) are optimized by local minimizers. This list of geometries is shortened from the nearly equivalent geometries by a dynamic single‐clustering analysis. The energy/gradient local minimizers act on the clustered list to produce a set of minima/stationary points. A targeted search of these points and reduction of the costs are reached by the way of several penalty functions. They eliminate—without energy calculation—most of the points generated by random walks on the potential energy surface. These penalty functions (on the total moment of inertia or on interatomic distances) are specific to the class of problem studied. They account for the nonrupture of either specific chemical bonds or rings in cyclic molecules, they assure that molecular systems are kept bonded, and they avoid the collapsing of atoms. © 1992 John Wiley & Sons, Inc.
Constrained self‐consistent‐field wave functions with improved long‐range behavior
Authors: Thakkar Ajit J. , Koga Toshikatsu , Matsuyama Hisashi , Archibong Edet F. 
Published: January 2005

AbstractThe recent suggestion that the long‐range behavior of energy‐optimized Gaussian basis sets can be improved by augmenting them with a Gaussian chosen to satisfy a constraint involving a linearly averaged position moment is explored. Calculations indicate that the high‐order moments 〈rk〉, with k > 4, in He, Be, and Li−, and 〈xkzL−k〉, with L > 4 and k ≤ L, in H2 are improved by the constraint, but that lower‐order moments and dipole polarizabilities are not. In H2, the higher moments with a given L improve by different amounts for different k, and, hence, the multipole moments do not improve. The basis‐set superposition error in HeHe and BeBe interaction energy calculations decreases if the internuclear distance is large enough. Thus, the constraint procedure improves the very long range behavior of the self‐consistent‐field wave functions. © 1992 John Wiley & Sons, Inc.
Experimental and computed bond lengths: The importance of their differences
Authors: Hargittai Magdolna , Hargittai István 
Published: January 2005

AbstractState‐of‐the‐art experimental electron diffraction and computational information on the structure of alkaline earth dihalide molecules are in agreement for the shape of these symmetric triatomic molecules (linear/bent/quasi‐linear). However, the computed and measured bond lengths show differences that are not only considerably larger than the experimental error but also have the wrong sign. The physical meaning of experimental bond lengths depends on the physical techniques used in their determination and the ways of averaging over molecular vibrations. The choice of model potentials in the elucidation of experimental information is also important, especially for floppy molecules. When improved computational bond lengths become available, their comparison with experimental information will have to take account of the physical meaning of the experimentally determined bond lengths. The computed equilibrium distance (re) should be smaller than the experimental distance‐average bond length (rg). The differences may range from a few thousandths of an Å to a few hundredths with increasing temperature and, especially, with increasing floppiness of the molecule. For truly accurate comparison, experimental bond lengths should be compared with computed ones only following necessary corrections, bringing all information involved in the comparison to a common denominator. © 1992 John Wiley & Sons, Inc.
Atomic integrals containing rrr with λ, μ, ν ≥ −2
Authors: Lüuchow A. , Kleindienst H. 
Published: January 2005

AbstractIn this paper, the efficient evaluation of the atomic integrals I =∫rrrrrre−αr1−βr2−γr3dτ with one or two factors r is described. These integrals are necessary for a lower‐bound calculation for Li‐like systems using the method of variance minimization or Temple's formula. © 1993 John Wiley & Sons, Inc.
Direct SCF structure optimization of large molecules on networks of workstations
Authors: Vogel S. , Hutter J. , Fischer T. H. , Lüthi H. P. 
Published: January 2005

AbstractA program to optimize the structure of large molecules at the Hartree–Fock level of theory running concurrently on a network of workstations is presented. Problems encountered in obtaining nearly optimal speedup and their solutions are discussed. A simple scheduling algorithm is presented that enables up to 99.5% of the code to run in parallel. © 1993 John Wiley & Sons, Inc.
Ab initio determination of polarizabilities per subunit in polymeric systems using the polarization propagator: Application to model hydrogen chains
Authors: Champagne Benoît , Mosley David H. , Fripiat Joseph G. , André Jean–Marie 
Published: January 2005

AbstractA procedure based on the polarization propagator technique is used to determine the longitudinal asymptotic electric polarizabilities per unit cell of infinite periodic systems. They are computed ab initio at the random‐phase approximation level of accuracy for infinite model hydrogen chains using the STO‐3G minimal basis set. This work also focuses on the effect of the number of interacting cells taken into account in the cell index summations as well as the number of k‐points needed to perform the integration in the first Brillouin zone. Long‐range effects are shown to influence the desired response properties more strongly than do short‐range effects. Our direct method is presented as the only way to get the asymptotic longitudinal polarizabilities per unit cell of the systems presenting the largest polarizabilities, the most interesting polymers. © 1993 John Wiley & Sons, Inc.
The N4 molecule has an open‐chain triplet C2h structure
Authors: Glukhovtsev Mikhail N. , Von Ragué Schleyer Paul 
Published: January 2005

AbstractThe lowest‐energy N4 is computed ab initio to be the planar C2h(3Bu) open‐chain structure 13. The open‐chain N4 singlet‐state structures dissociate on geometry optimization. The tetraazatetrahedrane Td structure 1 and the tetrazete D2h structure 2 are minima at MP2/6‐31G*. However, both are higher in energy than 13 (24.1 and 21.2 Kcal/mol [UQCISD) (T)(full)/6‐311+G*//MP2/6‐31G* + ZPE(MP2/6‐31G)*, respectively]. The energy of 13 is 157.5 kcal/mol higher than that of two N2(1∑ molecules [UQCISD(T)(Full)/6‐311+G*//MP2/6‐31G*] © 1993 John Wiley & Sons, Inc.
Accurate computation of the energy spectrum for potentials with multiminima
Authors: Taşeli Hasan 
Published: January 2005

AbstractThe eigenvalues of the Schrödinger equation with a polynomial potential are calculated accurately by means of the Rayleigh–Ritz variational method and a basis set of functions satisfying Dirichlet boundary conditions. The method is applied to the well potentials having one, two, and three minima. It is shown, in the entire range of coupling constants, that the basis set of trigonometric functions has the capability of yeilding the energy spectra of unbounded problems without any loss of convergence providing that the boundary value α remains greater than a critical value αcr. Only the computation of the nearly degenerate states of multiwell oscillators requires dealing with a relatively large truncation order. © 1993 John Wiley & Sons, Inc.
Graph factorization: A new mode of application of a vertex‐alternation scheme
Authors: Mukherjee Asok K. , Das Debes K. 
Published: January 2005

AbstractLinear chains where the vertex weights change sign alternantly but are equal in magnitude were able to be reduced to smaller chains by a procedure analogous to that given by Coulson and Rushbrooke. The algorithm for constructing the reduced chains has been stated and proved. The results have been utilized, in conjunction with McClelland's graph‐factorization method using reflection (σ) planes, to reduce the HMO secular determinants of some chemical graphs to an extent beyond the ability of group theory. McClelland's σ‐plane algorithm, used repetitively where possible, produces factors whose sizes (nM) are equal to those (nG) of the group‐theoretic factor blocks. For linear polyacenes (LP), however, a new observation has been made: If the LP has an even number of fused rings, nM = nG; but when the LP has an odd number of fused rings, McClelland's process is effective in further reduction, i.e., nM < nG. In any case, however, the vertex alternation procedure reported in the present paper brings about further reduction. To demonstrate the utility of the present method, a sample calculation of the LUMO eigenvector graph theoretically has been shown for p‐benzoquinone and the result has been utilized to obtain an inductive effect HMO parameter of the methyl group from the charge‐transfer bands of some molecular complexes of methylated p‐benzoquinones.© 1993 John Wiley & Sons, Inc.
Dipole, quadrupole, octupole, and dipole–dipole–quandrupole polarizabilities and second hyperpolarizabilities at real and imaginary frequencies for helium in the 23S state: Dispersion‐energy coefficients for interactions between He(23S) and H(12S), He(11S), He(23S), or H2(X1∑g+)
Authors: Bishop David M. , Pipin Janusz 
Published: January 2005

AbstractWe have determined the dynamic dipole (α1), quadrupole (α2), octupole (α3), and dipole–dipole–quadrupole (B) polarizabilities and the second hyperpolarizability tensor (γ) for the helium atom in its lowest triplet state (23S). We have done so for both real and imaginary frequencies: in the former case, for a range of frequencies (ω) between zero and the first electronic‐transition frequency, and in the latter case for a 32‐point Gauss–Legendre grid running from zero to ħω = 20 Eh. We have also determined the dispersion‐energy coefficients C6, C8, and C10 for the systems H(12S)He(23S), He(11S)He(23S), and He(23S)He(23S) and the C, C, C, C, and C coefficients for the interaction He(23S)H2(X1∑). Our values of the higher‐order multipolar polarizabilities and of γ for the 23S state of helium are, we believe, the first to be published. © 1993 John Wiley & Sons, Inc.
Electronic‐phase transition of the Hartree–Fock solution of the infinite one‐dimensional system: Structural change in an arbitrarily doped polyacetylene chain
Authors: Tanaka Kazuyoshi , Takata Akira , Okada Mayumi , Yamabe Tokio 
Published: January 2005

AbstractThe concept of the electronic‐phase transition of the Hartree–Fock solution has been applied to an arbitrarily doped polyacetylene (PA) chain to examine the structural change of the polymer skeletons under such doping regimes. It has been found that the n‐doped PA chain tends to suppress the generation of the charge‐density wave (CDW) phase, whereas the p‐doped PA favors the CDW phase leading to the charged‐soliton shape. © 1993 John Wiley & Sons, Inc.
Binding regions in polyatomic molecules
Authors: Wang Xiangyang , Peng Zhouren 
Published: January 2005

AbstractA justification of Berlin's theorem that concerns the binding force concept in diatomic molecules is presented based on the Hellmann–Feynman theorem and its electrostatic interpretations. The concepts of binding and the binding region first derived by Berlin for diatomic molecules are extended to polyatomic molecules; the virial of forces necessary to hold the nuclei in a molecule fixed is proved to be an exact description of the total binding effect in the molecule. The partition of molecular space into binding and antibinding regions based on the binding function, which is defined in this paper, is proposed for polyatomic molecules. The binding diagrams for some planar molecules are developed as simple applications of our theoretical considerations. © 1993 John Wiley & Sons, Inc.
Multipole moment analysis for hydrides, fluorides, and lithium compounds of first‐ and second‐row elements
Authors: Köster Andreas M. , Jug Karl 
Published: January 2005

AbstractA method is presented that conserves all local dipole moments in a partitioning of overlap charge between pairs of atoms. The approximate conservation of quadrupole and higher‐moment components can be used as a criterion for the suitability of atomic basis sets. Ab initio calculations are presented for hydrides, fluorides, and lithium compounds of first‐ and second‐row elements in a systematic study of compounds and basis sets. The best suitable basis set for each series is determined by the criterion of best approximate conservation of quadrupole moment components. A linear relation between charge shifts and Mulliken electronegativity differences is established for diatomic molecules. © 1993 John Wiley & Sons, Inc.
Calculation of two‐center exchange integrals with STOs using Möubius transformations
Authors: López R. , Ramírez G. 
Published: January 2005

AbstractThe Möbius transformations recently proposed for integrating functions with a sharp peak close to a single boundary of integration (H.H.H. Homeier and E.O. Steinborn, J. Comput. Phys. 87, 61, 1990) are used to extend Ruedenberg's algorithm for two‐center exchange integrals to cases with very diffuse STOs. © 1994 John Wiley & Sons, Inc.
Novel approach to molecular similarity: Second‐order similarity indices from geminal expansion of pair densities
Authors: Strnad Martin , Ponec Robert 
Published: January 2005

AbstractThe recently introduced second‐order similarity index gAB was generalized by using the geminal and/or spingeminal expansion of pair densities that they are derived from. The comparison with previous related studies confirms that the generalization does increase the information content of new indices, especially in providing the information about the difference in the spin recoupling of pure singlet and triplet states of electron pairs. Analogously, as in previous studies, the approach was applied to the analysis of several selected pericyclic reactions and possible mechanistic implications arising from the increased information content are briefly discussed. © 1994 John Wiley & Sons, Inc.
Energy levels of small titanium oxide clusters obtained from SCF calculations
Authors: Hagfeldt A. , Lunell S. , Sieghbahn H. O. G. 
Published: January 2005

AbstractThe energy levels of small titanium oxide clusters [(TiO2)2, and (TiO2H)3, and (TiO2H)2] have been calculated using ab initio SCF methods. Both crystal and relaxed geometries have been considered. Systematic changes in the valencelevel structure resulting from geometry relaxation are found, which may be related to band‐gap changes experimentally observed for small titanium oxide particles. In addition, a TiOH local surface state is found to be well described within a limited cluster model. © 1994 John Wiley & Sons, Inc.
Electronegativity, hardness, and a semiempirical density functional theory of chemical binding
Authors: Ghosh Swapan K. 
Published: January 2005

AbstractChemical binding is modeled through interatomic charge transfer and accumulation of electron density at the bond center using the concepts of electronegativity and hardness parameters defined for the bond region. The generalized electronegativity and hardness parameters for the up‐ and down‐spin electrons are also defined within the framework of spin‐polarized density functional theory, leading to the formulation of covalent binding in molecules in terms of a two‐way flow of unpaired electrons between the atoms. The associated energy changes corresponding to these descriptions are shown to provide quite accurate predictions of bond energies for simple heteronuclear diatomic molecules. © 1994 John Wiley & Sons, Inc.
Theoretical study on metal NMR chemical shifts: Germanium compounds
Authors: Nakatsuji H. , Nakao T. 
Published: January 2005

AbstractGermanium chemical shifts were studied theoretically by the ab initio molecular orbital method. The compounds studied were GeMe4−xClx and GeMe4−xHx(x = 0–4). The calculated values of the germanium chemical shifts agreed well with the available experimental values. The germanium chemical shift is due to the p‐electron mechanism that reflects the ligand electronic effect on the p‐p* excitation term in the second‐order paramagnetic term. For GeMe4−xHx, the chemical shift is almost linear to the number of the ligand, x. On the other hand, a U‐shaped dependence is predicted for the chemical shifts of the GeMe4−xClx series and is shown to be caused by the strong and nonadditive electron‐withdrawing ability of the Cl ligand. The diamagnetic contribution is relatively small for the chemical shift and is determined solely by a structural factor. © 1994 John Wiley & Sons, Inc.
Electron density distribution functions and the ASED–MO theory
Authors: Anderson Alfred B. 
Published: January 2005

AbstractA diatomic charge density distribution function may be partitioned into free atom and delocalization components. Integrating the electrostatic force on one of the nuclei as the atoms join to bond yields a repulsive atom superposition energy Er(R) and an attractive delocalization energy Ed(R) which, when added, equal the Born‐Oppenheimer potential energy, E(R). Bond stretch force constants may be calculated to quite good accuracy from the Poisson equation ▽E(R) = 4πZbpa(r = R), where Zb is the charge of nucleus b at a distance of R from nucleus a and pa is the charge‐density distribution function of isolated atom a. This equation follows if the delocalization density component is rigid during molecular vibrations and Ed = c/R, where c is a constant. Ed(R) is well approximated by the change in orbital energy, δEMO(R), for the bond‐forming reaction a + b → a ‐ b as obtained from a modified extended Hückel procedure. The resulting E() = Er(R) + δEMO(R) generalizes immediately to polyatomic molecules and solids and can be used for the calculation of structures and other properties and their molecular orbital interpretation. The current understanding of the atom superposition and electron delocalization molecular orbital (ASED‐MO) theory is presented in this article. It is pointed out that a parallel exists with the density functional theory, wherein the Born‐Oppenheimer potential function may be constructed from energy points E(R) that are functionals of the molecular charge density distribution function. Calculations of molecular structures with density functional theory has also become possible only through the introduction of electron orbitals. However, the approaches are otherwise different, for density functional theory works with the total energy of the molecule and the ASED approach works with the molecular binding energy obtained by integrating the electrostatic force on a nucleus, which is zero for the isolated atoms. © 1994 John Wiley & Sons, Inc.
Wannier analysis of the Cooper pairing force
Authors: Tachibana Akitomo 
Published: January 2005

AbstractIt is demonstrated that in the plasma state of the homogeneous electron gas the time‐reversal electron pair is stabilized. This nature survives even in the inhomogeneous electron gas, where the Bragg reflection at the lattice points is not necessarily a stumbling block for electron pairing. Indeed, a critical radius rc exists around the lattice point, outside of which the time‐reversal scattering state of the electron pair is guaranteed. The critical radius rc has an intrinsic importance as a measure of the coherence length ζ of the Cooper pair that exhibits the time‐reversal symmetry. © 1994 John Wiley & Sons, Inc.
Extended Koopmans' theorem ionization potentials for beryllium atom shake‐up transitions
Authors: Morrison Robert C. 
Published: January 2005

AbstractThe ionization potentials were calculated for Be using the extended Koopmans' theorem (EKT) using several full configuration interaction (CI) and multiconfigurational‐self‐consistent‐field (MCSCF) wave functions as reference wave functions. The wave functions used account for 89.7–96.7% of the correlation energy. Comparisons are made with experimental values and with δCI values calculated as the difference in energy obtained from CI wave functions for Be and Be+. The best EKT IP differed from the δCI value by 0.0003 eV for the lowest IP and by 0.0006 eV for ionization into the lowest 2P state of Be+. A calculation of ionization into the second 2P state of Be+ requires diffuse orbitals that are unimportant in the wave function for the ground state of Be. This results in small natural orbital occupation numbers for natural orbitals needed in the EKT calculation. © 1994 John Wiley & Sons, Inc.
Sensitivity analysis of charge transfer systems: In situ quantities, intersecting state model and its implications
Authors: Nalewajski Roman F. 
Published: January 2005

AbstractThe states of reactants in the donor (base, B)‐acceptor (acid, A) systems are examined and the charge transfer (CT) in situ sensitivities, including the chemical potential, hardness, softness, and Fukui function (FF) data, are derived within the atoms‐in‐molecules (AIM) resolution. Relaxational correction to the reactant CT FF vector is identified and qualitatively examined. The previously introduced intersecting state model (ISM) of the A‐B systems is generalized beyond the N‐restricted CT energy profile and formulated in terms of the intersecting energy paraboloids of reactants, within both uncoupled (qualitative) and coupled (quantitative) formulations; here, N is the total number of electrons. The model identifies the N‐unrestricted reaction paths in the AIM electron population space, possible when the system can exchange electrons with its environment and generally corresponding to a lower activation energy. The orientation of the reactant FF vector as a function of the hardness tensor structure is qualitatively examined in a model system consisting of two populational degrees of freedom (2 df), and the resulting conclusions are used to examine the mutual orientation of the hardness ellipses of the 2 df reactants in the A‐B systems. Predicted orientations and trends in activation barriers are discussed in the context of the hard‐soft acids and bases principle. © 1994 John Wiley & Sons, Inc.
Electron correlations and transport effective mass in narrow‐band systems and the Hubbard model
Authors: Arai Tadashi 
Published: January 2005

AbstractThe Hubbard model is rederived from a tight‐binding band calculation, showing that, as long as parameters are properly chosen, the model is justified for calculating electronic properties of narrow‐band systems. The treatment is extended by including correlations and it was found that bound solutions called dimers exist. The concept of dimers is found to be very powerful for understanding the unusual properties of heavy fermion systems. However, a Mott‐Hubbard‐like model may be required to calculate properties of high Tc cuprates. © 1994 John Wiley & Sons, Inc.