bluuebunny/crossref_metadata_2025_split huggingface dataset:
Approximate theoretical determination of molecular static polarizabilities
Authors: Seger G. , Kochanski E. 
Published: December 2004

AbstractMolecular polarizabilities are computed using ab initio SCF wave functions and second‐order perturbation theory with special attention given to the use of a shifted denominator. Rather small basis sets are used, in order to obtain reasonable values at a reduced cost. Results are presented for H2, CO, H2O, C2H4, OCS, C6H6, Cl2, Br2, I2.
Gaussian expansions of hydrogenic functions involving few variational parameters
Authors: Hoor Marten J. Ten 
Published: December 2004

AbstractFully optimized lengthy Gaussian expansions of hydrogenic 1s and 2pz functions have been practically reproduced by generating the variational parameters by means of suitably chosen functions involving only few parameters. Hydrogenic 3dxy and 4fxyz functions have been approximated in a similar way. The usefulness of such generating functions is briefly discussed.
Optical oscillator strengths for lithium
Authors: Ganas P. S. 
Published: December 2004

AbstractA simple two‐parameter analytic potential adjusted so as to reproduce the experimental energy levels is used to generate wave functions for the ground and excited states of the lithium atom. Using these wave functions in conjunction with the Born approximation and the Russell–Saunders LS‐coupling scheme, we calculate the optical oscillator strengths for various excitations from the 1s22s(2S1/2) ground state. The results are compared to experiment and other calculations.
Ab initio Hartree–Fock and multiple‐scattering Xα calculation of the g factors for CuF2
Authors: Larsson Sven , Hehenberger Michael , De Mello Paulo Corrêa 
Published: December 2004

AbstractAb initio Hartree–Fock and multiple‐scattering wave functions are calculated for linear CuF2. These wave functions are used to calculate the spin–orbit coupling in a new way where the neglect of two‐ and many‐center terms is avoided and where experimental or calculated spin–orbit coupling constants for the atomic ions are used. The calculated value of g is too small by the MSXα method and too large by the ab initio method, indicating too much 3d–L interaction in the MSXα case and too little in the ab initio case.
Modified PCILO method. II. Second‐order energy and geometry of transition‐metal halides
Authors: Boča R. , Pelikán P. 
Published: December 2004

AbstractThe modified PCILO method, for which the use of the Rayleigh–Schrödinger many‐body perturbation theory with the Møller–Plesset type of Hamiltonian partitioning is characteristic, has been extended to energy calculations of transition metal compounds. On the CNDO/2 level of the Hamiltonian approximation the energy and geometry of the ions CuX42−, MCl42− and the molecules CuX (X = F, Cl, Br; M = Mn, Fe, Co, Ni, Cu) have been calculated. The comparison with MOLCAOSCF calculations (CNDO/2–UHF) shows that the localized bonding model used here can be regarded as a good zeroth‐order approximation describing the bonding situation in complexes of this type. The perturbation theory also provides an improvement of the harmonic force constants of the CuX molecules with respect to the SCF level of approximation.
Absorption spectrum of manganian andalusite: Cluster calculation by an ab initio method
Authors: Hehenberger Michael , Hålenius Ulf , Larsson Sven 
Published: December 2004

AbstractThe ground state and the first few excited states of an MnO69− cluster are calculated in the unrestricted Hartree–Fock model. The state ordering is 5B1 g, 5A1 g, 5B2 g, and 5Eg as can be expected from simpler models. Consistent with the results by the same method for copper complexes, we obtain d–d transition energies about one half or less of the experimental energies. The charge transfer spectrum is subject to a large spin polarization in the sense that the lowest charge transfer state (5Eu) has five unpaired spins on Mn.
Classical nonlinear field theory of chemical bonding
Authors: Hartmann Hermann , Chung Kyu‐Myung 
Published: December 2004

AbstractA certain type of classical nonlinear field theory of chemical bonding has been proposed. The interaction between two neighboring atoms is assumed to be nonlinear. The coupled field equations are decoupled applying the methods of parametrization. The field energy associated with the coupled field has been determined perturbation theoretically. The chemical bonding energy equivalent to the change of field energy due to the coupling has been expressed in a closed form. The bonding energies of the molecules Li2, Na2, and K2 are evaluated.
Hypervirial analysis of enclosed quantum mechanical systems. I. Dirichlet boundary conditions
Authors: Fernández Francisco M. , Castro Eduardo A. 
Published: December 2004

AbstractDiagonal hypervirial relations are applied to enclosed one‐dimensional systems when wave functions obey Dirichlet boundary conditions. A general formula for the energy is derived and it shows a striking difference with the usual formulas through an “extra” term. It constitutes a generalization of previous ones for the virial theorem when there exist nonusual boundary conditions. The values obtained are compared with other approximate methods. Several extensions are proposed.
Some recent developments in the quantum theory of hydrogen bonding and other effects in proteins
Authors: Peters David , Peters Jane 
Published: December 2004

AbstractStandard ab initio quantum chemical computations are quite effective in throwing light on binding features of biomolecules, in particular, hydrogen bonds. This is illustrated by a brief survey of recent work, including some interesting preliminary results on dipeptides, tripeptides, and tetrapeptides. Differential‐energy maps for analyzing results are presented and discussed. Basic theoretical questions, such as the significance of minimal‐basis calculations and localization on a subsection of a macromolecule, are also discussed.
Potential energy surface of the system CO + O: An ab initio study on the OCO bond formation
Authors: Bonapasta A. Amore , Bossa M. , Lapiccirella A. 
Published: December 2004

AbstractQuantum mechanical computations on the potential energy surface of the system CO + O at an SCF–MO ab initio level are presented and discussed. The calculations are performed on a minimal basis set of atomic functions. Comparison with results obtained with extended basis sets are also presented.
Bond model for semiconducting materials
Authors: Garbato L. , Manca P. , Mula G. 
Published: December 2004

AbstractA bond model directly derived from an LCAO Hamiltonian is applied to the study of Group IV elemental semiconductors. The derivation has been made through suitable approximations of the interaction integrals. The average and the lowest energy gaps of C, Si, Ge, and α‐Sn are then computed with the use of just one parameter. The overall reliability of the model has been checked by computing the lattice dilatation contribution to the temperature coefficient of the lowest energy gap of Ge. The result is in excellent agreement with the experiment.
Structure and function of Buthus eupeus scorpion neurotoxins
Authors: Grishin E. V. 
Published: December 2004

AbstractAt present the investigation of the complex mechanism of the signal conductance between nerve cells and their target organ is closely connected with application of neurotoxins as a valuable tool for study of important sites involved in nerve transmission. Particular interest is attributed to neurotoxins from scorpion venoms which slow down the inactivation rate of fast sodium channels of the excitable membrane. Fifteen different toxins have been isolated from Buthus eupeus scorpion venom by means of the combination of gel and ion exchange chromatography. The homologous insectotoxins I1, I3, I4, and I5 belong to the new structural type of scorpion toxins. The essential features of these toxins are low molecular weight (ca. 4000) and the presence of two or three methionine residues in their amino acid compositions. The complete amino acid sequences of two insectotoxins and one mammalian toxin have been estimated. All mammalian neurotoxins in concentration from 10−9M to 10−7M slow down the inactivation rate of fast sodium channels. The direct covalent binding of photosensitive radioactive neurotoxin derivatives presents one of the most effective approaches to the localization of the functionally important components of the fast sodium channels. Thus far 2,4‐dinitro‐5‐fluorophenylazide has been used for chemical modification of the mammalian neurotoxin M10. The prepared monosubstituted photosensitive neurotoxin derivative possessed a high biological activity according to the voltage clamp data. The neurotoxin derivative has been iodinated by 125I, the resulted product being both radioactively and photoaffinity labeled. Both native neurotoxin M10 and sea anemone toxin competitively inhibit the reception of the scorpion toxin derivative by rat brain synaptosomes. It was shown that covalent toxin‐receptor complexes are composed of two protein components with molecular weights 76,000 and 51,000, being near equal for synaptosomes, neuroblastoma cells, and crab nerve plasma membranes.
Energy calculations on helical polypeptides: Structure of polyglycine II
Authors: Balaji V. N. 
Published: December 2004

AbstractSingle chain and packing energy calculations have been made on polyglycine (threefold and fourfold helical structures) with interchain NH…︁O hydrogen bonds. In conformation A of polyglycine, in which the NH groups point away from the helix axis and the CO groups are nearer to the helix axis, the conformational energy is nearly the same for threefold and fourfold structures. However, the minimum energy conformation corresponds to a threefold structure of polyglycine with peptide configurations in conformation B in which the CO groups point away from the helix axis and NH groups are nearer to the helix axis. This structure is consistent with the polyglycine II x‐ray diffraction data.
Van der Waals force between two localized clusters of bosons
Authors: Mishra R. K. , Bhaumik K. , Srivastava A. , Chaudhary S. S. 
Published: December 2004

AbstractIn traditional quantum electrodynamic derivation of a intermolecular van der Waals force, the molecules are assumed to be localized clusters of electrons. In this paper we have assumed the molecules to be localized clusters of bosons and have shown that the expression of the potential remains formally the same. This vindicates, through a microscopic derivation, the established concept that the van der Waals interaction is essentially a macroscopic phenomenon.
Structure factor calculations of various DNA duplexes
Authors: Bansal Manju , Gupta Goutam 
Published: December 2004

AbstractBased upon a stereochemical guideline, both right‐ and left‐handed duplexes were generated for A, B, and D forms of DNA using a mononucleotide as the repeat. Structure factor amplitudes were computed following two methods: (i) one employed an infinite helix as the motif and (ii) the other had an exact crystallographic repeat (e.g., 10 b.p. for B‐DNA) as the motif. Both the procedures showed that DNA in either handedness for A, B, and D forms of DNA are consistent with the observed fiber data. This observation is attributed to the fact that fibre pattern (resolved only upto 3 Å) only gives the image of the gross structure of the molecule. Thus, when the gross structure is suitably fitted to match the observed pattern, it is immaterial as to what the precise stereochemistry of the repeating unit (fine structure) and handedness of a model are. Sequence specific helical conformations were obtained using dinucleotide as the repeating unit. Helices fell into two classes: (i) right‐handed uniform (RU) and (ii) left‐handed zig‐zag (LZ) structures. A few aspects concerning the scattering profile of these helices are discussed.
Ionophores and channels
Authors: Ovchinnikov Yu. A. 
Published: December 2004

AbstractThe present state in the chemistry of peptides and proteins capable of transporting ions across biological and model membranes have been reviewed. The mechanisms of action of peptide ionophores valinomycin and enniatin and also the channel‐forming peptide gramicidin‐A have been discussed on the basis of spatial structure and dynamic conformational properties of the compounds. Recent progress in the studies of bacteriorhodopsin, cholinergic receptor from postsynaptic membrane, and sodium channel from the excitable nerve membrane, the integral membrane proteins acting as proton or metal ion channel formers is also discussed.
Application of NMR of oriented systems in biochemistry and biophysics
Authors: Khetrapal C. L. 
Published: December 2004

AbstractGeneral principles of NMR spectroscopy of oriented molecules are described. The use of the technique to problems of biological importance is discussed with emphasis on theoretical and experimental difficulties involved. Application of the technique to study the structure and the hindered rotation in N‐methylimidazole and phenyl silane, to investigate interactions of small molecules with lyotropic liquid crystals, to determine covalent and van der Waals radii, and to estimate non‐planar distortions in amides are described.
Effect of change of water structure on the phase transition of liposomes of dipalmitoyl phosphatidylcholine
Authors: Das Sudipto , Singhal Gaurishanker 
Published: December 2004

AbstractThe role of water structure around model membrane systems (e.g., liposomes) on phase transition of the lipid dipalmitoyl phosphatidylcholine was investigated. Water structure was altered by changing pH and by addition of solutes which are known breakers and makers of water structure. The structure makers broadened the zone of transition and changed the overall phase transition profile, while the main effect of structure breakers was to cause a shift in the transition temperature. The observed variation of Chapman transition temperature and broadening of zone of transition with varying pH is discussed in terms of altered water structure around the membrane–aqueous interface. Binding studies with the dye 1‐anilino‐8‐napthalene sulfonate showed that structure makers or breakers did not bind to the liposome surface directly. Thus the structure makers and breakers act on the membranes perhaps by altering the water structure differentially. Possible associated mechanisms of action are discussed.
Positron band structures for beryllium
Authors: Oriade Joseph Oladipo 
Published: December 2004

AbstractWe report on the band structure and wave functions of positrons, annihilating with electrons, from the thermalized state k+ = 0. We find that the bottom of the band to which the positron thermalizes in this metal is definitely nonambiguous. It is also found that even though the first few Bloch terms in the wave function can give the gross shape of the positron annihilation curve for this metal, the higher momentum components of high orders are definitely important if one is to assay the fine details of the curve.
Symmetry simplifications of space types in configuration interaction induced by orbital degeneracy
Authors: Balasubramanian K. 
Published: December 2004

AbstractSymmetry simplifications are introduced in configuration interaction (CI) by reducing the number of symmetry‐allowed space types if there is degeneracy in some of the molecular orbitals by constructing the unique space types. A new symmetry group which we call the configuration symmetry group is defined and is shown to be expressible as a generalized wreath product group. Generating functions are derived for enumerating the equivalence classes of space types. A double coset method is expounded which constructs the representatives of all equivalence classes of space types using the cycle index of generalized wreath product and the double cosets of label subgroup with generalized wreath product in the symmetric group Sn, if n is twice the number of occupied and virtual orbitals. Method is illustrated with CI using the localized orbitals of polyenes, CI in benzene, and atomic CI for several reference states.
Variational‐Perturbation theory in the LCAO‐MO method for closed‐shell molecules
Authors: Malykhanov Yu. B. 
Published: December 2004

AbstractUsing the variational principle, equations have been obtained for density matrix of molecules with the external perturbation of the common type present. The perturbed wave function was taken as a superposition of the ground and single‐excited configurations made of the Hartree‐Fock molecular spin orbitals. On the basis of these equations a series of variants of static perturbation theory have been worked out for the ground and excited states of closed‐shell molecules.
Molecular tight‐binding method. I. Many‐electron method for hole bands of molecular crystals
Authors: Stolarczyk Leszek Z. 
Published: December 2004

AbstractA method for calculating ab initio electronic excitation energies of molecular crystals, based on a many‐electron tight‐binding approximation, is described. The method follows Frenkel's model for excitons and allows a many‐electron treatment of the band‐structure problem of molecular crystals. The case of hole bands is studied in detail and various versions of the method are considered. A computational scheme is proposed, in which approximate correlation corrections to the HFR matrix equations of the one‐electron LCMO method are calculated. The main effects contributing to these corrections are the effect of relaxation of a molecular ion, the effect of intramolecular electronic‐correlation change, and the effect of polarization of the remaining molecules in a crystal. The method developed in the present paper is applied to calculation of the hole bands of the HCP helium crystal.
Equation matricielle de Hartree‐Fock permettant de déterminer la nième harmonique
Authors: Smet F. , Van Groenendael A. 
Published: December 2004

AbstractThe system of time‐dependent Hartree‐Fock equations allowing the calculation the of nth harmonic generation is established by using the same method used in a former paper in the same conditions. These equations are still subjected to orthonormalization conditions. Then by using a recurrence method, we express these equations in matrix form, as well as the orthonormalization conditions; and, as in the former paper, we then replace the solution of the matrix equation subjected to a constraint by that of a free equation. Finally the elimination of the spin variables allows a further simplification. So we obtain an equation allowing the calculation of the nth harmonic generation.
Analysis of the covalent bond: One center floating functions for the hydrogen molecule ion
Authors: Hurley A. C. 
Published: December 2004

AbstractThe roles of kinetic and potential energy operators in the formation of a chemical bond are investigated using the virial and electrostatic theorems. It is shown that an integrated form of the virial theorem throws a new light on a paradox involving changes in the mean kinetic energy on bond formation. Detailed calculations on the ground state of H lead to a surprisingly simple electrostatic approximation to the bond. The entire potential curve is given to good accuracy (ca. 80% bond energy) by the electrostatic forces between the two protons and a single, nodeless, spherically symmetric charge cloud representing the electron, provided that, if the bond is stretched beyond about 3.6 a.u. the charge cloud switches suddenly from a central location to a position near one proton.
Coordinate rotated TDHF excitation energies Li− 1S → 1P
Authors: Nielsen Egon S. , Simons Jack 
Published: December 2004

AbstractWe present the first application of the coordinate rotation method, within the time‐dependent Hartree–Fock framework, to calculation of positions and widths of metastable excited states. The method is briefly outlined and results of its application to 1P excited states of Li− are given. Comparison of our results to those obtained using electron scattering methods by other workers is also made.
Structures, stabilities, and energies of isomerization of α‐cyano and α‐isocyano carbanions
Authors: Moffat J. B. 
Published: December 2004

AbstractAb initio STO‐3G calculations show that α‐cyano‐ and α‐isocyano‐substitution on carbanions produce a significant approximately equal stabilization of these charged species. Evidence is presented which suggests that the mechanism of such stabilization is qualitatively different for the cyano and isocyano substituents. The former appears to act through an electron delocalization process while the latter may operate by an inductive effect.
Instabilities of the symmetry‐adapted restricted‐hartree–fock ground state in infinite polyenes. I. Singlet instabilities
Authors: Karadakov P. , Castan̄o O. 
Published: December 2004

AbstractThe singlet instabilities of the RHF ground state in infinite polyenes have been studied in the framework of a semiempirical PPP Hamiltonian, accounting for long‐range Coulomb interactions until convergence of the ground‐state energy per electron value. The symmetry‐adapted RHF solution (SAS) has been shown to be unstable to the formation of bond‐order alternation waves (BAW's) and charge‐density waves (CDW's). The CDW solutions have been shown to be higher in energy than the corresponding BAW solutions and to represent saddle points of the energy hypersurface, unstable to the formation of BAW's for physically realistic range of variation of the semiempirical parameters. Analytical formulas for the SAS ground‐state energy per electron have been derived in case of a Coulomb law and a Mataga–Nishimoto formula for the two‐center Coulomb integrals.
New method for the direct calculation of electron density in many‐electron systems. I. Application to closed‐shell atoms
Authors: Deb B. M. , Ghosh S. K. 
Published: December 2004

AbstractA new density‐functional equation is suggested for the direct calculation of electron density ρ(r) in many‐electron systems. This employs a kinetic energy functional T2 + f(r)T0, where T2 is the original Weizsäcker correction, T0 is the Thomas–Fermi term, and f(r) is a correction factor that depends on both r and the number of electrons N. Using the Hartree–Fock relation between the kinetic and the exchange energy density, and a nonlocal approximation to the latter, the kinetic energy–density functional is written (in a.u.)

where \documentclass{article}\pagestyle{empty}\begin{document}$ C_k = {\raise0.7ex\hbox{$2$} \!\mathord{\left/ {\vphantom {2 {10}}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{${10}$}}(3\pi ^2)^{2/3} $\end{document}. Incorporating the above expression in the total energy density functional and minimizing the latter subject to N representability conditions for ρ(r) result in an Euler–Lagrange nonlinear second‐order differential equation

where μ is the chemical potential, we have ρ(r) = |ϕ(r)|2, and g(r) is related to f(r). Numerical solutions of the above equation for Ne, Ar, Kr, and Xe, by modeling f(r) and g(r) as simple sums over Gaussians, show excellent agreement with the corresponding Hartree–Fock ground‐state densities and energies, indicating that this is likely to be a promising method for calculating fairly accurate electron densities in atoms and molecules.