bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long‐range interaction between 1s and 2s or 2p hydrogen atoms
Authors: Kołos W. 
Published: December 2004

AbstractLong‐range interaction energy between two hydrogen atoms has been computed in the second order of the perturbation theory. All states of the system arising when one of the atoms is in the 1s and the other in the 2s or 2p state have been considered. The energy represented by a series expansion in inverse powers of the internuclear distance, R, has been computed up to the terms in R−8. The results are believed to give reliable interaction energies for R > 15 a.u. Accurate interaction energy for two ground‐state hydrogen atoms has also been obtained up to the terms in R−10. Results for the B′ 1∑ state are employed to discuss the experimental ground‐state dissociation energy of H2, D2, and HD. For H2 all values of the dissociation energy obtained from various experimental absorption limits, by using the computed potential energy curve to separate off the effect of rotation, are shown to be satisfactorily consistent. The resulting total energy of H2 is, however, higher than the most accurate theoretical value.
Geometric approximation for molecular polarizabiities
Authors: Howat G. , Trsic M. , Goscinski O. 
Published: December 2004

AbstractMolecular polarizabilities calculated with the geometric approximation are shown to be independent of the type of perturbation theory used. Agreement with finite field calculations, including anisotropies, is obtained for small molecules. A modified procedure for including sigma and pi contributions in a differentiated way is developed within the CNDO scheme. Applications to planar conjugated systems are displayed.
Etude Quantique du Pouvoir Rotatoire Naturel et de la Biréfringence Gyrotropique dans un Cristal
Authors: Duprez‐Quesnoit C. 
Published: December 2004

AbstractA quantum calculation of the optical activity and gyrotropic birefringence is used in a molecular crystal to deduce symmetry properties. A study of the variation of the components of these tensors, when a change of origin occurs, is used to account for the formula for the electric excitation proposed by Landau and Lifchitz. It is shown that the results obtained are valid in the case of crystals with nonlocalized electrons.
Using group (or Loge) functions to explore the transferability of chemical bonds
Authors: Sanchez M. , Daudel R. , Dacre P. D. , McWeeny R. , Kwun S. , Valdemoro C. 
Published: December 2004

AbstractThe transferability of bonds in a set of small molecules has been explored. The molecular wave‐functions have been calculated from the group (or loge) function method, via a construction based on Gaussian functions. The transferability is very good and the effect of lone pairs on adjacent bonds has been analysed. Furthermore, a very simple procedure has been proposed to estimate the frontiers of the bonds.
PCILO Calculations on charge transfer complexes
Authors: Lochmann R. , Hofmann H.‐J. 
Published: December 2004

AbstractThe equilibrium distances of the complex components and the stabilization energies were calculated for the molecular complexes ethylene–fluorine, ethylene–chlorine, tetracyanoethylene–benzene, tetracyanoethylene–durene, and quinone–hydroquinone using the PCILO method. The results are compared with the experimental values and the theoretical predictions of the CNDO/2 method.
Effect of semi‐empirical parameters on the simple random‐phase approximation calculations of conjugated hydrocarbons
Authors: Niyogi B. Guha , Mukherjee D. C. , Sannigrahi A. B. 
Published: December 2004

AbstractSinglet‐singlet transition energies, oscillator strengths, triplet energy levels, and the ground state correlation energy of a number of conjugated hydrocarbons have been calculated by the simple random‐phase approximation (RPA) within the framework of the Pariser‐Parr‐Pople (PPP) model. The effect of semi‐empirical parameters in such calculations has been examined in detail. A set of parameters has been deduced from these parametric studies which is found to yield results for the singlet spectra of the molecules in excellent agreement with experiment. It is, however, not possible to treat the triplet states using these same parameters, since they produce triplet instabilities in all the molecules. The triplet instability problem associated with semi‐empirical RPA calculations has been discussed in detail.
Angular dependence of Gaussian‐Lobe orbitals. III. Polyhedric lobe edifices
Authors: Le Rouzo H. , Silvi B. 
Published: December 2004

AbstractAn analysis is presented that shows how the angular symmetry defects of lobe orbitals constructed from a polyhedric edifice can be accurately evaluated, and how these lobe orbitals can be related to harmonic Gaussian functions, the exponents being tranferred by a scale factor procedure.
Atomic dipole approximation and energies of interactions between purine and pyrimidine bases. I. Electrostatic interactions of adenine with uracil, thymine, thiouracils, dihydrouracil, and 5‐fluorouracil
Authors: Geller M. , Jaworski A. , Pohorille A. 
Published: December 2004

AbstractThe atomic dipole approximation has been employed to calculate the energies of electrostatic interaction between adenine and various pyrimidine derivatives. Minima of the interaction energy for various planar configurations were determined. Inclusion of the “monopole–dipole” and “dipole–dipole” terms in the multipole expansion improves considerably the agreement with experimental data. The effect of sulfur substitution has been investigated in detail. Formation of NH…︁S hydrogen bonds is less favorable than of NH…︁O bonds, due largely to the lower atomic dipole of the sulfur atom resulting from the shift of the π‐electron charge toward the neighboring carbon. The results are relevant to the interactions of thiouracils in nucleic acids.
Theoretical studies of hemoproteins. I. Mathematical description of the allosteric effect
Authors: Kikuchi Takeshi , Nishimoto Kichisuke 
Published: December 2004

AbstractA new theoretical approach to the cooperativity of an enzyme has been proposed. When we applied the present theory to the allosteric effect of hemoglobin, we obtained a so‐called Koshland–Nemethy–Filmer formula. Our theory suggested that the sigmoid curve becomes sharper when the affinity of the first oxygen molecule of the hemoglobin is smaller.
Valence photoelectron spectrum of CoO. Ab initio calculations of energies and relative intensities within a limited CI framework
Authors: Wahlgren Ulf , Johansen Helge 
Published: December 2004

AbstractThe valence spectrum of CoO has been calculated using the CoO610− cluster, stabilized by an electrostatic field, as a model of bulk CoO. The wave functions were generated using basis sets of better than double‐zeta quality. SCF wave functions were obtained for the ground state and for the first ionized state of the cluster. Limited CI calculations were performed using these orbital sets. The lowest states of the ion correspond to the main lines in the spectrum, while higher states can give rise to high‐energy satellites to the main lines. The relative intensities of these satellites were estimated in the case of high‐energy incident photons.
Spin‐Free configuration‐interaction study of molecules using single‐parameter alternat molecular orbitals
Authors: Sarma C. R. , Dinesha K. V. 
Published: December 2004

AbstractA procedure is outlined for a programmable spin‐free configuration‐interaction (CI) study in molecules using single‐parameter alternant molecular orbitals for generating various configurations. The configurations were chosen to form bases for the irreducible representation {2N/2–2, 12S} of the general linear group GL(n). Using a transformation to biorthogonal space the CI matrix elements of a spin‐free Hamiltonian were generated. The procedure has been used to obtain the π‐electron energies for the 3,1Ag and 3,1Bu states of cis‐ and trans‐butadiene.
Hydrophobic “pocket” on photosynthesizing membrane near photosystem II
Authors: Yasnikov A. A. , Volkova N. V. , Kanivets N. P. , Mushketik L. S. , Vasilenok L. I. , Kukhar' V. P. , Pavlenko A. F. 
Published: December 2004

AbstractStudies concerning the effect of 2‐alkyl pyridine N‐oxides with different substituents on electron transfer, phosphorylation, and light‐dependent proton transport in photosynthesizing membranes of chloroplasts were conducted. It is determined that 2‐alkyl pyridine N‐oxides with short alkyl chains stimulate the Hill reaction and light‐dependent proton transport inside chloroplasts. Compounds having alkyl residues with 6‐10 carbon atoms in the chain inhibit electron transport, ADP phosphorylation, and reduction of ferrocyanide in thylakoids. A conclusion is drawn on the presence of the hydrophobic “pocket,” which is of importance for organization of the electron‐transport chain of chloroplasts, near photosystem II.
Intensities of spin‐forbidden transitions in molecular oxygen and selective heavy‐atom effects
Authors: Minaev B. F. 
Published: December 2004

AbstractIntensities of a1Δg←X 3∑g− and b 1∑g+ ← X 3∑g− transitions in molecular oxygen have been calculated on the basis of the INDO method taking into account spin‐orbit coupling by perturbation theory. The transitions are magnetic dipole in nature. The first of them (a − X) steals its intensity from 3Πg‐3∑g− and 1Πg‐1Δg transitions, which are determined by the orbital angular‐momentum operator. This source is not the principal one for the intensity of the second (b‐X) transition. Its intensity is stolen principally from microwave transitions between spin sublevels of the ground 3∑g− state. The last source explains the large difference in intensities of the a‐X and b‐X transitions. Calculated oscillator strengths are in a good agreement with experiment. The same integrals that determine the intensity also determine the parameters of the spin Hamiltonian for the ground 3∑g− state. These parameters are in a good agreement with experiment also, showing the validity of the whole calculation. In a condensed phase the investigated transitions are enhanced by intermolecular exchange interaction. It is known that an external heavy atom (EHA) enhances the b‐X transition of oxygen in solution, but does not influence the a‐X transition. In the collision complex O2‐EHA, which has a geometry without inversion symmetry, the microwave transitions between spin sublevels of the “3∑g−” state obtain electric‐dipole moments, which are stolen from the charge‐transfer transition. This mechanism explains the selective effect of EHA.
Notes on hydrogenic Gaussian lobe functions
Authors: Hoor Marten J. Ten 
Published: December 2004

AbstractThe Gaussian lobe representation of 2p and 3dxy functions of a one‐electron atom has been reconsidered. Contrary to earlier results, it has been found that the minimum energy associated with the simplest case of these functions is reached when the expansion centers coincide with the nucleus. This also seems to be true for representations with larger expansion lengths. Under similar conditions, Whitten's octahedral representation of the 2p function gives a better energy value than Poshusta's tetrahedral one.
Ab initio calculation of ESCA satellite intensities for a copper–chlorine complex
Authors: Larsson S. , de Mello P. Corrêa , Hehenberger M. 
Published: December 2004

AbstractAb initio SCF calculations carried out on the planar cluster CuCl42− suggest that the strong satellites at the high‐binding energy side of inner‐shell ESCA lines of Cu are due to charge relaxations in the σ‐bonding orbitals which mix with Cu 3d. The satellite state with the largest intensity may be described as a one‐electron excitation Cu 3d → Cl 3p.
SCF Theory of multiplet states
Authors: Carbó R. , Domingo Ll. , Gregori J. 
Published: December 2004

AbstractThe SCF theory of multiplet monodeterminantal states is described from a comprehensive viewpoint. In this context, the formalism and derived theorems are developed, as well as the description of a SCF closed‐shell‐like structure, namely the hypermultiplet. Numerical applications are discussed taking as a model the H2O molecule and its first positive ion. Wave functions of double ζ‐quality, with computed molecular properties of 16 states are given.
Electron correlation effects in SCF+CI wave functions—Fermi and coulomb correlation holes in HCN
Authors: Cooper Ian L. , Pounder Christopher N. M. 
Published: December 2004

AbstractThe Coulomb correlation hole distribution function has been computed with respect to various reference centers in the HCN molecule, using standard SCF+CI type wave functions. The extent to which statistical correlation between unlike‐spin electrons is introduced into an SCF wave function through the inclusion of configuration interaction has been assessed by an examination of the range and depth of such holes, and compared with the behavior of analogous Fermi distribution functions. Our results show that the range of Fermi correlation is consistently longer than that of the corresponding Coulomb correlation.
Theoretical study of some Van der Waals molecules
Authors: Kołos W. , Corongiu G. , Clementi E. 
Published: December 2004

AbstractThe Van der Waals molecules Ar · HF, Ar · H2O, and Ar · HCl have been analyzed with potential surfaces obtained by SCF energies corrected for the basis set superposition error and by including dispersion forces. The computed properties for these Van der Waals molecules are in good agreement with recent experimental observations.
Normal‐mode vibrational frequencies and thermodynamic properties of uracil and 4‐hydroxyuracil
Authors: Shibata Masayuki , Zielinski Theresa Julia , Rein Robert 
Published: December 2004

AbstractNormal‐mode vibrational frequencies were obtained for uracil and 4‐hydroxyuracil with the MINDO/3 SCF method. MINDO/3 vibrational frequencies and the moments of inertia for STO‐3G optimized geometries yielded a ΔS for U ⇄ U* of 1.06 e.u./mol by standard statistical thermodynamic equations. ΔG is then 6.29 kcal/mol in the gas phase for U ⇄ U*. The reaction field continuum model of solvent effect lowers ΔG to 5.3 kcal/mol in aqueous solution. The tautomeric equilibrium constant in solution is then 1.3 × 10−4, in good agreement with experimental values.
Regression analysis of enzyme reaction. O‐methylation of catechol derivatives by catechol‐O‐methyltransferase
Authors: Shinagawa Yasuko , Shinagawa Yoshiya 
Published: December 2004

AbstractThe electronic structures of catechol derivatives, 3,4‐dihydroxy‐1‐substituted benzenes, including epinephrine and norepinephrine, were calculated by means of the CNDO/2 and the MINDO/3 methods. Correlation between the maximum velocities divided by the molecular weight, as between the inverse of Michaelis–Menten constants in the O‐methylation reaction catalyzed by catechol‐O‐methyltransferase and the electronic indices calculated on the basis of the frontier electron theory was found. The correlation coefficient between the observed maximum velocities divided by the molecular weight and the calculated ones was 0.873. The regression analysis showed that the Coulombic forces at the C3 and C4 positions and the electron acceptable indices at C6 and meta‐O positions represented the best correlation with the biological activities (Vmax and Km). The electronic indices of the catechol moieties represent the rate‐limiting factor of the O‐methylation reaction.
V‐Coupling coefficients from SO(3) to the octahedral group
Authors: Au‐Chin Tang , Ching‐Yu Cho , Chia‐Chung Sun 
Published: December 2004

AbstractThe properties of V‐coupling coefficients from SO(3) to the octahedral group are discussed and, for the purpose of practical use in ligand field theory, the numerical values from j = 1/2 to j = 12 1/2 have been worked out through an Elliott‐503 computer. The values for j ≤ 4 1/2 are listed.
LCAO‐MO treatment for deep levels produced by ion implantation of oxygen in gallium arsenide
Authors: Ruo‐Zhuang Liu , Wen‐Lin Feng 
Published: December 2004

AbstractThe ion implantation of oxygen in either n or p‐type gallium arsenide results in the formation of a semi‐insulating layer that is thermally stable. There still is no reasonable explanation for this phenomenon (except one of us has made a preliminary investigationSee Ref. 1.
). In this paper, we simulate the crystal of GaAs by a molecular cluster. As is well known the molecular‐cluster model has a shortcoming in introducing “surface states” owing to the dangling of atomic bonds on the surfaces.See Ref. 2.
In order to suppress this effect, the dangling bonds were saturated with hydrogen atoms as proposed by Larkins.See Ref. 3.
Therefore, in this paper the perfect crystal of GaAs was simulated by a cluster of atoms with a composition Ga4As13H36 (which corresponds to a pseudocluster Ga13As13). In the authors' opinion, this kind of treatment may cause minor changes in the positions of a few energy levels, but the general energy diagram pattern will reflect the main features of the real crystal. The electronic states of the entire system are then computed by an LCAO‐MO technique (extended‐Hückel theory). The substitutional oxygen OAs, the arsenic vacancy VAs, and the OAsVAs complex are treated similarly. The results of the calculation show that the substitutional oxygen (OAs) forms deep donor levels in the forbidden gap. The arsenic vacancy also forms donor levels in the forbidden gap. On the other hand, the OAsVAs complex forms deep acceptor levels in the forbidden gap. Thus we have given a reasonable model for the mechanism of the formation of an insulating layer produced by oxygen ion implantation in GaAs.
Microscopic theory of the average band gap of semiconductors
Authors: Van Doren V. E. , Van Camp P. E. , Devreese J. T. 
Published: December 2004

AbstractIn Phillips' spectroscopic theory of semiconductors, the covalency and ionicity are derived empirically from the average band gap between the highest valence and lowest conduction bands. In this paper an explicit expression for the average band gap is derived based on a continued fraction representation of the polarizability matrix. Results of a calculation for six covalent and polar semiconductors, using the pseudopotential model, are presented and compare favorably with experimental values.
N2 Laser‐excited luminescence of antiferromagnetically coupled trinuclear chromium(III) complexes
Authors: Morita Makoto , Kato Yoshiaki 
Published: December 2004

AbstractExchange interaction parameters in several trinuclear chromium(III) complexes [Cr3O(R‐COO)6(H2O)3]X·nH2O (R = CH3, C2H5) are determined in the study of luminescence, time‐resolved luminescence (TRS), and decay time measurements over the temperature range 4–100°K. The presence of four inequivalent trinuclear clusters and a luminescence anomaly at 25 and 55°K are observed in the basic chromium(III) acetate prisms. Magnetic anomalies reported earlier should be attributed to the distortion and disordering of the hydrogen‐bonded channels in crystals at low temperatures.
Synchrotron radiation spectroscopy of quasi‐one‐dimensional materials
Authors: Mitani T. , Suga S. , Tokura Y. , Koyama K. , Nakada I. , Koda T. 
Published: December 2004

AbstractThe optical reflectivity spectra of quasi‐one‐dimensional polymers (SN)x, trans‐(CH)x, and polydiacetylene are investigated in an energy range from 1 to 25 eV by use of synchrotron radiation. Observed structures associated with π‐electron states are interpreted in terms of the quasi‐one‐dimensional one‐electron bands calculated by the LCAO‐type model.
Variational functions of the padé type—application to the ground state of the helium atom
Authors: Jolly P. , Saxena R. P. , Srivastava P. K. , Sane K. V. 
Published: December 2004

AbstractIt is shown that trial functions involving Padé approximants yield satisfactory results for the ground state of the helium atom. In particular, the five‐parameter form reproduces the best variational function of the type Ψ = e–zsϕ(u) obtained numerically, to a remarkable extent.
Multipole polarizabilities and shielding factors of the hydrogen atom from the hydrodynamic analogy to quantum mechanics. III
Authors: Shukla G. C. , Issa M. R. , Narayan M. S. 
Published: December 2004

AbstractVariational iterative solutions for multipole polarizabilities of the H atom have been carried out. The resulting numerical values of the Cauchy coefficients are in harmony with our recent work. The large frequency expansion of the multipole polarizabilities of the H atom is also calculated. The first term in such expansions, the multipole oscillator strength sum rule, is in harmony with earlier work.
Experimental designs for finding stationary points and for computing force constant matrix
Authors: Sana M. 
Published: December 2004

AbstractWe use an experimental design method for computing a local quadratic form which is adequate to find stationary points and to evaluate the force constant matrix on a k‐dimensional potential energy hypersurface. Two types of designs are particularly discussed: the composite and the Doehiert's plane. We give examples for illustrating the methodology. Some thermodynamical properties are deduced from our results. Such a method may be used with every type of theoretical calculations (SCF or CI) and with any program without modification.
A scaled “one‐electron Hamiltonian” model for open‐shell LCAO–MO–SCF calculations
Authors: Bhattacharyya Sankar Prasad 
Published: December 2004

AbstractAn approximate technique of generating orthonormality‐constrained one‐electron orbitals for the description of open‐shell systems is suggested. The “off‐diagonal Lagrangian‐multiplier problem” is circumvented by using a common potential for both the closed‐ and open‐shell electrons. This common potential is generated by a scaling of the usual exchange potential of Hartree–Fock theory. The problem of choosing an appropriate scaling parameter (μ) is considered from both variational and perturbative points of view. The relationship of the present method with some other approximate open‐shell theories is explored. The numerical results of computations carried out at the semiempirical MO level are presented in order to bring to light the dependence of computed molecular properties on the magnitude of the scaling parameter.
n‐Local energies as accuracy measures on approximate wave functions
Authors: Grelland Hans H. 
Published: December 2004

AbstractA class of multilocal functions called n‐local energies, which can serve as accuracy criteria on approximate wave functions, are defined. Their interpretation is discussed and their multilocal form is shown to be a result of the holistic character of the quantum description. The analogy with the reduced local energy of Thomas, Javor, and Rothstein is demonstrated. The explicit formula for the simplest n‐local energy capable of measuring the deviation from the exact solutions of the Schrödinger equation is obtained in the one‐determinantal case.