bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uniform quality gaussian basis sets for molecular calculations. IV. Gradient and charged optimized basis sets for CH4
Authors: Poirier Raymond A. , Daudel Raymond , Csizmadia Imre G. 
Published: December 2004

AbstractComparison of the molecular Q‐optimized and molecular gradient optimized carbon basis sets for CH4 showed that molecular Q optimization is an excellent substitute to the more expensive molecular gradient optimization. The parameter Q of the Q optimization is related to the population (i.e., net charge) on the atom.
Dna‐Dependent rna polymerase from E. coli: Structure investigation
Authors: Marchenko T. V. , Lipkin V. M. , Yu. Chertov O. , Sverdlov E. D. , Ovchinnikov Yu. A. 
Published: December 2004

AbstractE. Coli RNA polymerase holoenzyme consists of two large subunits—β and β' (molecular weights 155,000 and 165,000), of two identical α subunits (molecular weight 36,500), and of the initiation factor α (molecular weight 86,000). The complete amino acid sequence of the RNA polymerase α subunit was determined. According to the primary structure the polypeptide chain of the α subunit has a molecular weight of 36,512 and consists of 329 amino acid residues. In order to determine the primary structure of large β and β' subunits of E. coli RNA polymerase, the protein fragmentation and sequencing procedure was combined with sequencing of the corresponding structural genes, which facilitated the ordering of the peptide fragments obtained during sequencing of the polypeptide chains. In all, 4714 base pairs of the rpoBC operon were sequenced including the entire structural gene of the β subunit and an initial segment (528 base pairs) of the β' structural gene. The β subunit appeared to consist of 1342 amino acid residues from which molecular mass was calculated to be 150618.6 daltons. The spatial organization of DNA‐dependent RNA polymerase was studied with the aid of chemical modification and limited proteolysis. Photochemical affinity modifications were used to find out subunits of the enzyme responsible for binding of the DNA template and the RNA product.
Molecular orbital studies on nucleoside antibiotics. IV. conformation of 3'‐deoxyadenosine (cordycepin) and 3'‐amino‐3'‐deoxyadenosine
Authors: Saran Anil , Patnaik Lalit N. 
Published: December 2004

AbstractPCILO computations have been carried out on the conformation of 3'‐deoxyadenosine (cordycepin) and 3'‐amino‐3'‐deoxyadenosine. These nucleoside antibiotics results as a consequence of modification in the sugar part of adenosine. Both C(2')‐endo and C(3')‐endo sugar puckerings have been considered in the computations and the results obtained indicate that these nucleoside antibiotics have very similar conformational preferences as compared to those of the parent nucleoside adenosine. This similarity which is quite marked in aqueous solution has important biological significance.
Significance of the electron trap parameters of glow curves of photosynthetic membranes
Authors: Tatake V. G. 
Published: December 2004

AbstractSeveral methods are available to determine the electron trap parameters such as activation energy E, preexponential frequency factor s, and the lifetime τ of the electrons in the trap states in photosynthesis. These parameters are also related by the Arrhenius expression which helps in calculating the E values without any assumptions regarding the particular order of kinetics applicable or the values of preexponential factors. Subsequent calculation then yields the values for s and τ in a straightforward manner. However, application of these methods (as well as the Arrhenius expression) to some of the experimental data has recently yielded such values that give rise to some questions regarding the meaning attributable to these parameters. The significance of these findings are discussed in view of the correlation of thermoluminescence and delayed light emission studies in photosynthetic membranes.
Active transport in the light of thermodynamics of open systems
Authors: Panda B. C. 
Published: December 2004

AbstractA brief thermodynamic analysis of transport processes in open systems is presented. It is shown that the concept of an active transport in the usual sense of the existence of a flow against the direction of its conjugate force is operationally unrealistic. The so‐called metabolically coupled active transport has been shown to be mathematically falacious. The experimental establishment in favor of the active transport process by the use of metabolic inhibitors has been logically disproven. From this analysis it is naturally concluded that all transport processes in the living organisms can be reduced to passive ones if one recognizes all the possible potential gradients existing in the system. Assuming the existence of active transport process is as erroneous as taking for granted a vital force explaining the life phenomena. It simply indicates our lack of knowledge about the pattern of superposition of a complete set of driving forces or about the nature of a yet unknown physical driving force and the generating mechanism of such a force.
Relationship of correlation energy and size
Authors: Ang M. H. , Yates K. , Csizmadia I. G. , Daudel R. 
Published: December 2004

AbstractAnalysis of available data on atoms has led to a relatively simple empirical relationship between the correlation energy and second moment <r2>, a measure of the size of the electron density. With the aid of this simple relationship it is possible to predict correlation energies with fair accuracy given the SCF or Hartree–Fock limit values for the size of the electron density. Preliminary extensions of this work to two‐ and ten‐electron molecules indicate that it may be possible to predict molecular correlation energies to semiquantitative accuracy from SCF data on the electronic distribution.
Inclusion of hydrogen p orbitals in the semiempirical calculation of NMR parameters. III: INDO CHF calculations of orbital and dipolar contributions to spin–spin coupling constants involving protons
Authors: Facelli J. C. , Contreras R. H. 
Published: December 2004

AbstractThe self‐consistent perturbation theory is used to calculate noncontract contributions to spin–spin coupling constants involving protons. Molecular wave functions were obtained with a modified version of the INDO method which includes hydrogen 2p orbitals in its basis set. It is found that in many cases the orbital and dipolar terms are by no means negligible, being particularly important in geminal HH couplings. Results reported in this paper for this type of coupling, reproduce experimental trends in the series CH4, NH3, and OH2. In general, noncontact terms are found to decrease as the number of bonds separating the interacting nuclei increases.
Self‐Consistent APW–k · p method. II. Application to NaCl
Authors: Da Cunha Lima I. C. , Da Silva A. Ferreira , Parada N. J. 
Published: December 2004

AbstractThe self‐consistent APW–k · p method is utilized to obtain the band structure of NaCl in the “muffin‐tin” approximation. Qe have investigated the convergence of many intermediate results, e.g., crystalline potential, matrix elements of the momentum operator, and energy eigenvalues at the Γ point. The summation in reciprocal space, included in the definition of the matrix D of the theory, is performed by direct sum and also by a special points technique. For the convergence criteria used, the results converged after five iterations.
Calculation of one‐electron properties using limited configuration interaction techniques
Authors: Raghavachari Krishnan , Pople John A. 
Published: December 2004

AbstractOne‐electron properties may be evaluated by configuration interaction methods using analytical differentiation of the total energy with respect to an external perturbation parameter. Dipole moments are reported using such a method for CO and H2CO. Inclusion of single substitutions does not change calculated dipole moments appreciably with this method. The differences between this method and the direct evaluation of an expectation value are discussed.
Computer‐generated formulas for two‐center coulomb integrals over slater‒ type orbitals
Authors: Jones Herbert W. 
Published: December 2004

AbstractFormulas can be automatically generated for all two‐center Coulomb integrals over Slater‐type orbitals by means of the “C‐matrix” single‐center expansion method with use of “computer algebra.” The formula coefficients may be stored in two‐dimensional arrays.
Perturbation theory in large order for some elementary systems
Authors: Bender Carl M. 
Published: December 2004

AbstractReasons for understanding the general problem of perturbation theory in large order are discussed. It is shown that the behavior of perturbation theory in larger order is generally very simple because it reflects just the semiclassical content of the theory. Many simple examples are given, including some graph‐counting problems. The behavior of mass‐renormalized perturbation series for some very simple field‐theory models is examined. It is shown that mass renormalization hardly affects the large‐order behavior of a weak‐coupling perturbation series. However, in a strong‐coupling perturbation series mass renormalization has a dramatic effect.
Unified derivation of the perturbation series for the real and imaginary parts of the energy of hydrogen in the stark effect and of the negatively anharmonic oscillator
Authors: Silverstone Harris J. 
Published: December 2004

AbstractThe wave function for hydrogen in the Stark effect (or for the negatively anharmonic oscillator) with an outgoing‐wave boundary condition, constructed in Langer‐Cherry fJWKB form, is continued back to the origin. The asymptotic expansions for ReE and ImE are determined by the requirement that the wave function be regular at the origin to zeroth and first order in the exponentially small parameter that characterizes ImE. One fJWKB function turns out to be the Rayleigh‐Schrödinger perturbation theory wave function.
Numerical estimates of the convergence of the Rayleigh‐Schrödinger perturbation expansions for the energy levels of various models of the benzene molecule
Authors: Pellegatti Alain , Čížek Jiří , Paldus Josef 
Published: December 2004

AbstractWe estimate radii of convergence of the Rayleigh‐Schrödinger perturbation expansions for various energy levels of the π‐electron model of the benzene molecule, described by the Hubbard Hamiltonian in both weakly and strongly correlated limits. They are determined using a “generalized” Cauchy criterion applied to the numerically determined coefficients of the pertinent expansions.
Superoperator approach to propagator approximations
Authors: Weiner Brian , Goscinski Osvaldo 
Published: December 2004

AbstractThe superoperator formalism for matrix propagators is reviewed, with special attention to the validity of superoperator resolution of the identity. The equation of motion for the particle‐hole propagator is discussed. Decoupling procedures based on inner projections and partitioning are examined showing the desirability of self‐consistent approximations. The conditions under which a state can be a vacuum for a given linear manifold of operators are analyzed.
Coupling of internal rotations in propanelike molecules
Authors: Wesenberg G. , Weinhold F. 
Published: December 2004

AbstractA linear‐combination‐of‐bond‐orbitals (LCBO) formulation of INDO–SCF–MO theory is employed to investigate the origin of rotation barrier coupling in propane and related molecules. The dominant contributions to rotor coupling in propane are identified to be (i) a direct steric (bond–bond) interaction, involving the close approach of two methyl CH bonds in the eclipsed–eclipsed geometry, and (ii) a nonvicinal bond–antibond effect, which arises when the side of a σCH bond orbital in an eclipsed methyl group comes into favorable overlap with the “backside” lobe of the coplanar σ antibond in the staggered–eclipsed geometry. A smaller nonadditive interaction of each methyl rotor with the central group is noted to be of importance when the central atom contains lone pairs. Aspects of this qualitative picture, and its dependence on geometry changes, are tested in applications to (CH3)2CHF, (CH3)2NH, (CH3)2O, (CH3)2CCH2, (CH3)2CO, and C(CH3)4.
Ab initio Hartree–Fock–Slater calculation of Tetrathiafulvalene (TTF) and the TTF1+ and TTF2+ ions
Authors: Trsic M. , Laidlaw W. G. 
Published: December 2004

AbstractThe electronic structures of TTF, TTF1+, and TTF2+ are described by means of an ab initio Hartree–Fock–Slater procedure with a double‐zeta STO basis. Electronic and photoemission spectra, bonding, and charge distributions are discussed and compared to experiments and previous calculations.
Connections between perturbation theory and the Van Vleck transformation: Illustrative calculations on the perturbed harmonic oscillator
Authors: Westhaus Paul 
Published: December 2004

AbstractWe continue to examine the connection between perturbation theory and the Van Vleck unitary transformation. Here we illustrate the formalism derived earlier by applying it to compute the stationary states of the perturbed harmonic oscillator. We find that each solution of the traditional Brillouin‐Wigner perturbation theory equations gives rise to a different unitary transformation which, when operating on the unperturbed ground state, produces one or the other of the perturbed eigenstates. With any of the perturbed states able to be reached by a unitary transformation on the unperturbed ground state, we advise caution in using approximate solutions of the perturbation equations in general cases, lest an unexpected stationary state be obtained.
Construction of an effective hamiltonian for open‐shell molecular systems
Authors: Biskupič Stanislav , Kvasnička Vladimír 
Published: December 2004

AbstractAn effective Hamiltonian for open‐shell molecular systems is constructed. The unrestricted Hartree–Fock orbitals are applied as a basis set of one‐particle functions. This effective Hamiltonian is determined as a simple product of the original total Hamiltonian and the spin annihilator. The second‐quantization formalism and the Feynman–Goldstone diagrammatic technique are used. The resulting effective hamiltonian is composed of zero‐ to four‐particle terms. A possibility of applying the nondegenerate diagrammatic perturbation theory constructed over this effective Hamiltonian is discussed.
Charge and spin correlation structures of conjugated π systems: Analysis of full CI wave functions of the PPP hamiltonian
Authors: Hashimoto Katsufumi 
Published: December 2004

AbstractAn analysis of the electronic correlation structures by means of the charge and spin correlation functions is carried out for full CI wave functions of four, five, and six membered conjugated π systems described by the Pariser–Parr–Pople Hamiltonian. The low‐lying states of these systems are classified as covalent (CV) and ionic (IN) states depending on whether the probability of finding two electrons simultaneously at the same position is small or large. It is found that many of excited CV states, the typical ones of which are the 21Ag state of linear π systems, have stronger CV character than the ground CV state, and their spin coupling structures are different from each other as well as from that of the ground CV state. The spin coupling structure in the ground CV state has an “antiferromagnetic” spin arrangement in favor of antiparallel coupling between nearest neighbor spins while in excited CV states the extent of the antiparallel spin coupling between nearest neighbor sites is decreased. IN states, which are less common for low‐lying states than CV ones, are also found to have characteristic modulations in the charge correlation. In particular, the charge correlations in the lowest singlet IN states, 11Bu of linear π systems, 11B2g of cyclobutadiene and 11B1U of benzene, are alternating.
Reduced local energy as a criterion for the accuracy of approximate Hartree–Fock wave functions. Application to H2O and CH4
Authors: Grelland Hans H. , Almlöf Jan 
Published: December 2004

AbstractThe reduced local energy EL of Rothstein and co‐workers is discussed as a criterion for the local accuracy of approximate wave functions. The behavior of EL for different approximation levels is discussed. It is shown that, for particular classes of wave functions, fluctuations of EL reflect local inaccuracies of the wave function as compared to certain convergence limits. The applicability of this criterion is illustrated with approximate Hartree–Fock wave functions for water and methane.
Evaluation of two‐center overlap and coulomb integrals derived from slater‐type orbitals
Authors: Jones Herbert W. 
Published: December 2004

AbstractThe strategy for the evaluation of two‐center overlap and Coulomb integrals is illustrated by using computer‐generated formulas produced from 1s orbitals. There is no loss in generality as these formulas have the same structure for higher quantum numbers. For small parameter values, singularities may be removed from the formulas by expanding exponential functions and collecting coefficients of like powers by machine. Suitable terminated expansions, along with exact formulas, permit high accuracy throughout the entire possible range of parameter values.
Quantitative structure activity relationships for some antitumor platinum(II) complexes
Authors: Abdul‐Ahad P. G. , Webb G. A. 
Published: December 2004

AbstractThe INDO–SCF method is used to provide electronic indices which are used as independent variables. These attempt to account for the variation in the antitumor activity and toxicity observed within a series of analogs of cis‐diamino dichloro platinum(II).
Two‐body operator matrix elements for pure and mixed orbital configurations in the unitary group approach
Authors: Kent R. D. , Schlesinger M. 
Published: December 2004

AbstractA complete list of expressions is given covering all possible types of nontrivial two‐body operator matrix elements in the unitary group approach. The matrix elements are expressed in terms of factors which depend on the unique spin coupling chain indicated by each Weyl tableau. The method applies equally to pure and mixed orbital configurations. The results extend and clarify previous general treatments of Drake and Schlesinger and Paldus and Boyle. We worked out two examples of 3(ƒ4) matrix elements of V4. V4 interaction and of 4(ƒ5)→4([2(ƒ3)]d2) matrix elements of V1 · V1 interaction.
Remarks on the use of the average occupation numbers in the SCF process for open shell systems
Authors: Colle Renato , Salvetti Oriano 
Published: December 2004

AbstractIt is shown that the utilization of an average occupation number for open shell orbitals, having different occupation numbers in a degenerate wave function, tantamounts to disregard first order contributions in a CI‐type expansion of the wave function. These contributions are taken into account in a SCF process that derives the differently occupied open shell orbitals as eigenfunctions of different Fock‐type operators and accounts for the total symmetry.
Generalized Euler transformation in extracting useful information from divergent (asymptotic) perturbation series and the construction of Padé approximants
Authors: Bhattacharyya Kamal 
Published: December 2004

AbstractEuler transformation for accelerating convergence of a series is considered in the context of handling divergent (asymptotically convergent) perturbation series. A generalized (parametrized) version of this transformation is developed, based on the conjecture of Dalgarno and Stewart, which works better. Viewed from this standpoint, the Padé approximants follow as a special case of the parametrized Euler transformation (PET), as is the case with the μ transformation procedure of Feenberg in a perturbative context. The PET is shown to serve as a more general method of handling a divergent series and is able to appreciate the construction and convergence behavior of specific sequences of Padé approximants. The role of parametrization in the context of the Z−1 perturbation theory of atoms is also noted and the workability of the adopted strategy is demonstrated by choosing some specific test cases.
Unrestricted‐Hartree–Fock wave functions approximating low‐lying covalent states of ring π systems
Authors: Hashimoto Katsufumi 
Published: December 2004

AbstractWe show that spin projected unrestricted‐Hartree–Fock (PUHF) wave functions are able to well approximate some low‐lying covalent states of ring π systems. The UHF wave functions belong to either the axial or torsional spin density wave class. Their spin structures are found to be approximations for the spin correlation structures of the corresponding exact wave functions. The PUHF wave functions become close to exact eigenstates with homopolar valence bond characters in the strong correlation limit.
Dilated Weyl theory applied to a set of N‐coupled singular second‐order differential equations
Authors: Elander Nils , Rittby Magnus , Brändas Erkki 
Published: December 2004

AbstractWeyl's theory for a set of N‐coupled singular second‐order differential equations is analyzed in relation to S‐matrix theory and a dilated version is presented. Applications of this theory to two single channel scattering model problems and a two‐channel model problem are given. Some implications of the present theory are discussed.
Kinetic theory of bridge processes
Authors: Christophorov L. N. , Gorbach V. V. , Kharkyanen V. N. 
Published: December 2004

AbstractThe detailed consideration of the kinetic aspect of the bridge process has allowed us to correctly write a kinetic equation beginning with knowledge of system microparameters. The solution of the equations makes it possible to elucidate the character of the relaxation process and to determine its typical constants as functions of those microparameters. Particular attention was given to kinetics in the presence of polaron effects. In this case the standard perturbation theory applied to derive the kinetic equations is not valid. The solutions obtained for this case are different both in the form of correlation functions and in the character of the interaction taken into account.
Localized bond model for molecular energy to fourth order in perturbation theory
Authors: Cullen John M. , Zerner Michael C. 
Published: December 2004

AbstractThe localized bond model of Malrieu, Diner, and Claverie is extended to fourth order in perturbation theory. Single, double, triple, and quadruple replacements from the doubly occupied bonding reference function are included utilizing a symmetric form of diagrammatic perturbation theory. The fourth order theory derived executes on a computer as quickly as does the third order theory. Results are examined utilizing the Pariser–Parr–Pople and CNDO/2 model Hamiltonians, and are compared with third order results and with either exact results where they are known, or with a configuration interaction of all singles and doubles. The influence of the initial hybridization, localization, and bond polarization is discussed. In general, the fourth order corrections are of comparable size to third order. Improvement in results appears to be marginal in the Nesbet–Epstein scheme in passing to fourth order because of the oscillating nature of the series; for Moller–Plesset theory errors are approximately halved. The relative energies as a function of modest geometry change about minima is about the same at third order as it is at fourth for most cases examined.