bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of mutations. II. Physical model of genetic stability
Authors: Cooper W. Grant 
Published: December 2004

AbstractA physical model for genetic stability of DNA is constructed in terms of the “microscopic” model for uninduced point mutations and the electromechanical thermoelastic properties of the macroscopic “global” DNA system. Theoretical considerations show how experimental data from one of the least complicated but useful genetic systems, T4 bacteriophage, support the proton‐code model of DNA discussed by Löwdin. The stability of an unperturbed DNA system is treated to illustrate the dynamical coupling between the “global” motion of DNA and the stability at local genetic sites. The method for analyzing a DNA system perturbed by “low‐energy” optical or acoustical frequencies is indicated. The model provides a physical explanation for “hot spots” (genetic sites highly susceptible to mutation) and suggests that quantum theory may be as useful in the biological sciences as it is in the physical sciences with respect to designing and interpreting certain experiments in genetics. The incidence of human cancer as a function of chronological age is discussed in terms of the model.
A direct CI method with a multiconfigurational reference state
Authors: Roos Björn O. , Siegbahn Per E. M. 
Published: December 2004

AbstractA method for direct configuration–interaction (CI) calculations with a multiconfigurational reference function is described. The reference state can contain several closed‐shell electronic configurations and the CI expansion comprises all single and double replacements out of all these configurations. The resulting secular problem is solved using a variation‐perturbation method. A number of examples are given showing the efficiency of the method. The largest CI expansion used in calculations with this program so far contains 76,471 spin‐ and space‐symmetrized configurations.
Floating spherical Gaussian orbital model study of some hydrogen‐bridged systems: LiBeH3, LiBH4, LiCH5, and BeBH5
Authors: Bhargava Shobha , Ray N. K. 
Published: December 2004

AbstractThe floating spherical Gaussian orbital (FSGO) method has been used to study the equilibrium geometries and electronic structures of some hydrogen‐bridged systems containing lithium, beryllium, boron, and carbon. The predicted geometries are in good agreement with other theoretical estimates. The binding energies for these hydrogen‐bridged systems are estimated and discussed. The FSGO total energies (EFSGO), for all systems studied here, are found to be well correlated to nuclear–nuclear repulsion (Vnn) and nuclear–electron attraction (Vne) terms by a relation of the type EFSGO =\documentclass{article}\pagestyle{empty}\begin{document}$ {\textstyle{3 \over 7}} $\end{document} (2 Vnn + Vne).
New method for approximate Hartree–Fock calculations using density approximations and coulomb field corrections. I
Authors: Noack Wolf‐Eckart 
Published: December 2004

AbstractA method is proposed that reduces the computational effort of HF calculations considerably by reducing the number of two‐electron integrals that have to be calculated. The following concepts are used: (i) approximation of the electron density by only few functions for the Coulomb part of the HF matrix; (ii) modification of this approximate density, to improve its Coulomb field; (iii) in the exchange part, a basis function χ is replaced by a function \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi $\end{document} consisting of fewer Gaussian lobes; (iv) the error caused by this replacement is reduced by a modification of the densities \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \chi _i \tilde \chi _j $\end{document} in the exchange integrals. The computation time of the integral part is reduced by a factor 6 for molecules containing five first‐row atoms as, e.g., CF4, if one uses a 7S/3P basis set contracted to (5, 1, 1/3). The integral time increases roughly with n3, if n is the number of Gaussian lobes.
New method for approximate Hartree‐Fock calculations using density approximations and coulomb field corrections. II
Authors: Noack Wolf‐Eckart 
Published: December 2004

AbstractThe HF approximation method that was outlined in Paper I is tested with respect to several molecular properties. Three different levels of approximation a, b, and c are considered. Satisfactory results—compared to corresponding “exact” HF calculations—are obtained with the STO‐3G basis and the approximation level a. At this level the error in the binding energy is 0.001–0.025 a.u. for all considered molecules which contain up to six first‐row atoms as, e.g., cyclopentanone (C5OH8). The error in the reaction energies considered here is about 4 kcal/mol (the maximal error is 9 kcal/mol). Orbital energies, dipole moments, gross charges, equilibrium geometries, and barriers to internal rotation are well reproduced by the approximation method at all three levels.
Analyses of the electronic collective motions by means of a nonlinear dynamical equation
Authors: Toyoda Kaoru 
Published: December 2004

AbstractA nonlinear dynamical equation for the electronic collective motion is presented by employing the traditional time‐dependent procedure. The equation is applied to the model π‐electron system of ethylene, and the effects of nonlinear interactions are investigated using its several states as reference states. It is shown that the nonlinear correlation plays an important role in describing the change of the lower excited states.
Ab initio molecular fragment calculations with pseudopotentials. Some fragments containing nitrogen and oxygen
Authors: Gáspár R. , Gáspár R. 
Published: December 2004

AbstractParameters for the OH (sp2) and NH3 (planar, sp2) pseudopotential–FSGO molecular fragments have been established in this paper. Calculations for the molecules of formic acid, formaldehyde, and formamide show good agreement with experiment.
Experimental evidence on the chemisorption bond of two‐ and one‐dimensional boundaries
Authors: Kern R. 
Published: December 2004

AbstractThis paper is intended to provide an experimentalist's contribution to a critical discussion of adsorption energies and their significance. The experimental requirements, with special reference to the limitations and the quality of the information provided by the various techniques are briefly reviewed. The significance of the measurements, and the background theoretical (phenomenological and model) schemes which experimentalists use for interpreting their results, are discussed in order to show that the interpretations of surface measurements must be carefully analyzed by theoreticians intending to contribute to an understanding of surface bonding.
State of ions near a cathode: Adions or adatoms?
Authors: Laforgue‐Kantzer D. 
Published: December 2004

AbstractIt is the intent of this article to illustrate certain aspects of the present status of electrochemistry as regards theoretical interpretations. First a brief critical review of classical electrochemical kinetics is given and the directions are indicated in which improvement in theoretical treatments are hardly needed. Next, experimental results on the cathodic discharge of tin in darkness and in light are presented, and a tentative explanation based on the assumption that adatoms (and not adions) diffuse on the electrode surface as a result of stabilization by light is presented.
Bond polarization in the FeCO system: Semiempirical MO–SCF (BMV) calculations
Authors: Barbier C. , Vincent C. , Del Re G. 
Published: December 2004

AbstractCharge distributions in FeCO for different Fe–C distances and the Fe–C–O angle equal to 180° and 90° have been computed by the BMV method, a semiempirical SCF scheme including overlap and especially suited for transition‐metal atoms. A comparison with available EHT and ab initio calculations suggests that the BMV method is a useful complement to ab initio calculations. The information obtained on the dependence of the binding in FeCO on the Fe–C distance is also briefly discussed in connection with the views of experimentalists of the state of CO absorbed on iron.
Diamagnetism as a structure and bonding related property in semiconductors
Authors: Garbato L. , Manca P. , Spiga A. 
Published: December 2004

AbstractThe reformulation of the quantum mechanical expression of the diamagnetic susceptibility, in terms of bond and band related parameters, leads us to evaluate separately the Langevin and the Van Vleck components of the lattice magnetic susceptibility of semiconductors. Its validity, checked for a number of semiconductors covering seven different structures and almost the entire range of variability of Suchet's ionicity parameter, confirms that a definite link exists between the diamagnetism of semiconductors and dielectrics and the nature of their interatomic bonds.
Neutron elastic scattering studies of biological molecules and complexes
Authors: Chidambaram R. 
Published: December 2004

AbstractNeutron diffraction can provide very precise stereochemical information about hydrogen bonds and other features involving hydrogen atoms in crystals. This is because, unlike for x rays, the hydrogen atom has a significant scattering amplitude for neutrons relative to other atoms. High‐precision studies of a class of molecules, like those on α‐amino acids carried out at Brookhaven and Trombay, can provide important information on systematics of the structure, conformation, and hydrogen bonding parameters. Some attempts have also been made to extend these single‐crystal studies to some proteins like myoglobin, lysozyme, and trypsin. The large anomalous scattering amplitudes for some stable isotopes like 113Cd and 149Sm and the easy variability of neutron wavelength also provides, in principle, a method for solving the phase problem without crystallizing too many heavy atom derivatives. The combination of neutron and x‐ray diffraction data, now being used to study charge density distributions in organic molecules and hydrogen bonds, may be extended in the future to larger molecules of biological importance. The small‐angle scattering of neutrons is also a powerful technique for studying large biological particles in solution at low resolution to obtain information about sizes, shapes and distribution of constituents.
MSW–SCF–Xα studies of some silicon compounds. I. Iminosilicon (HNSi)
Authors: Scheire L. , Rotthier R. , Phariseau P. 
Published: December 2004

AbstractMSW–SCF–Xα calculations have been carried out to obtain ionization potentials (via Slater's transition state concept) and charge distributions for HNSi. The results are interpreted and compared with previous ab initio and CNDO/2 studies.
Variants of Rayleigh–Schrödinger perturbation theory—a new look
Authors: Bhattacharyya Kamal 
Published: December 2004

AbstractSeveral useful “redefined zero‐order Hamiltonian” variants of the Rayleigh–Schrödinger perturbation theory are derived by exploiting the freedom of choice for the orthogonality integral between zero‐ and first‐order wavefunctions. It is found that the more common Hamiltonian repartitioning schemes follow quite naturally, as a consequence of certain consistency requirements. The strategy adopted may as well be employed to derive various newer and profitable zero‐order Hamiltonians depending on the nature of the problems. This implication is strengthened by demonstrating the calculational success of one such derived scheme. Feenberg's “scale‐changed” Hamiltonian approach is also reinterpreted in the present context.
Meaning of the perturbation theory for a class of multiple‐well anharmonic oscillators
Authors: Graffi S. 
Published: December 2004

AbstractIt is proved that the Borel sum of the Rayleigh‐Schrödinger perturbation expansion eigenvalue of the triple well anharmonic oscillators p2 + x2 − 2g2nx2n+2 + g4nx4n+2, g > 0, n = 2.3,… is a complex eigenvalue of a different problem. Its relation with the eigenvalues of the original Hamiltonian is discussed.
Some remarks on the use of rational functions as variational functions
Authors: Jolly P. , Sane K. V. , Saxena R. P. , Srivastava P. K. 
Published: December 2004

AbstractWhen a Padé‐type function is used as a trial function, it is necessary to investigate the location of singularities and the zeros of the optimized function. It is shown that an unacceptable wave function can sometimes yield numerically acceptable values because of the nature of the integration procedure. It is also shown that it is possible to remove the undesirable features of a lower order form by invoking the next approximation.
Relation of the charge and spin correlation functions to the structures of π electron wave functions in alternant hydrocarbons
Authors: Hashimoto Katsufumi 
Published: December 2004

AbstractWe analyze, in the Pariser–Parr–Pople (PPP) model of alternant hydrocarbons, how the charge and spin correlation functions (CF's) are related to the structure of a CI wave function and the MO's of the systems. The analysis is based on the fact that an uncorrelated electron present in an orbital does not contribute to the linked dynamically correlated parts of the CF's. By using the fact, simple rules are deduced predicting the covalent or ionic nature of the correlation structure in a low‐lying state with two correlated electrons. The rules predict that the singlet minus and triplet plus states are covalent, while singlet plus and triplet minus states are ionic, where the plus and minus mean the alternancy symmetry. The rules also give a prediction for the unknown charge and spin correlation structures between different sites.
Calculation of systems involving strong delocalized bonds within a modified PCILO framework. I. Valence‐bond PCILO method
Authors: Lochmann R. , Weller Th. 
Published: December 2004

AbstractIn describing mesomer structures by the original PCILO method several problems may occur because of the use of localized bonds. A so‐called VB‐PCILO including a superposition of several mesomer boundary structures in the CI perturbation treatment will be proposed.
Ab initio calculations of guanidinium–carboxylate interaction
Authors: Sapse A. M. , Russell C. S. 
Published: December 2004

AbstractAb initio calculations (self‐consistent‐field Hartree–Fock) using 6‐31G and STO‐4G basis sets are used to investigate the interaction between guanidinium and methylguanidinium ion with the carboxylate group of formate. Binding energies and optimum geometries are obtained and compared with reported results using a smaller basis set (STO‐3G). The importance of this interaction in proteinsubstrate binding is discussed.
Approximate symmetries in the singly excited states of helium
Authors: Flurry R. L. 
Published: December 2004

AbstractConsideration of R(4) as the degeneracy group for the singly excited states of helium allows the assignment of R(4) irreducible representations (irreps) to these states. Induction of these irreps onto the irreps of SU(4) and U(4) provides a sufficient number of invariants to define the energy levels. Empirical equations allow all of the singlet states to be related to the first ionization energy and the Rydberg constant, to a good approximation. Empirical equations can also be derived for the triplet states, but their relation to the ionization energy and/or the Rydberg constant is not obvious.
On a unified treatment of kinetics and diffusion, and a connection to a nonlocal boltzmann equation
Authors: Ulmer W. 
Published: December 2004

AbstractFick's law of diffusion has been generalized to include kinetic processes, the transport term of the Boltzmann equation, and nonlocal interaction processes. It is shown that the collision interaction term can be obtained by the introduction of a quantum stochastic potential equation. Some approximations of a nonlocal Boltzmann equation can be solved exactly. The solutions can be applied to problems of molecular pattern in biology.
The INDO/2‐AHP (average hole potential) method for excited states: Comparison with the simple INDO/2‐HP (hole potential) method
Authors: Banerjee Manas , Bhattacharyya Sankar Prasad 
Published: December 2004

AbstractThe INDO/2 version of the average hole potential (AHP) model is analyzed. The model is applied to study the geometric features, molecular inversion barriers, singlet‐triplet splittings, etc., of a few small carbonyl molecules (H2CO, HFCO, F2CO) in the 1,3nπ* states with partial as well as complete optimization of all geometric parameters in the excited states. The results are compared with those obtained by a simple hole‐potential (HP) model.
On the relationship between the electron‐pair distribution function and the correlation energy of an atom
Authors: Ugalde J. M. , Boyd Russell J. 
Published: December 2004

AbstractThe pair distribution function h(r12;r1, γ) and the virial theorem are used to derive a general expression for the local contributions to the total correlation energy of an atom. A direct link between correlation effects and the correlation energy is obtained by use of G(r1, γ) and Γ(r1, y). The former is the probability associated with a given choice of r1 and γ, while the latter describes the local contribution to the correlation energy. Explicit calculations for the ground state of helium indicate that the angular dependence of the local contribution to the correlation energy is essentially independent of r1, whereas the local correlation energy shows a strong r1 dependence. The maximum contribution to the correlation energy occurs at intermediate values of γ where there is close agreement between the Hartree–Fock and exact densities.
The quantum mechanical many‐body problem in hyperspherical coordinates. Analysis of systems with coulomb interactions in terms of many‐dimensional hydrogen‐like wave functions
Authors: Avery John , Larsen Peter Sommer , Hengyi Shen 
Published: December 2004

AbstractA method is described for using many‐dimensional hydrogen‐like wave functions as a starting point for constructing solutions to the Schrödinger equation of an N‐particle system. The solutions are built up from symmetry‐adapted hyperspherical harmonics, multiplied by functions of the hyperradius, r. Approximate asymptotic solutions for large values of r are discussed, as well as approximate solutions valid near r = 0. Properties of hyperspherical harmonics are discussed. General methods are presented for resolving arbitrary functions into hyperspherical harmonics and for constructing simultaneous eigenfunctions of generalized angular momentum and total orbital angular momentum.
Optical properties of large molecules and clusters in the frenkel exciton picture
Authors: Avery John , Hvidt Søren 
Published: December 2004

AbstractFrenkel exciton theory is reviewed. This theory yields general formulas relating the absorption and circular dichroism spectra of large molecules or clusters to the optical properties of their subunits. It is shown that for weakly interacting systems, the circular dichroism associated with a band of exciton states is proportional to tr(FH), where F is an “optical matrix” constructed from the positions and transition dipole moments of the subunits, and H is an interaction‐energy matrix. It is shown that if a system expnds isotropically, then tr(FH) falls off as the inverse square of the linear dimensions. This result is compared with experimental measurements of the low‐temperature optical rotatory dispersion of proteins as a function of temperature. The optical properties of helical polymers are also discussed as a function of their geometrical parameters.
Toward the variational treatment of spin‐orbit and other relativistic effects for heavy atoms and molecules
Authors: Hess Bernd A. , Buenker Robert J. , Chandra Praphull 
Published: December 2004

AbstractObservation of trends in computed spin‐orbit splittings for relatively light molecules leads to the conclusion that relativistic corrections to the electronic charge distribution are important when treating molecules containing heavy atoms (Z > 18). In order to preserve the nature of the successful computational techniques currently applied to light molecules in so far as possible, particularly to allow for the treatment of correlation effects in an efficient CI procedure on an equal footing with relativistic effects, emphasis is placed on the development of a two‐component formalism for this purpose. A first attempt in this direction consists of formulating a spin‐free quantum mechanical operator that reflects relativistic kinematics. The mass‐velocity term in the Breit‐Pauli Hamiltonian is not appropriate for a variational treatment, however, since it drastically alters the spectrum and gives results that are not bounded from below. To avoid this problem the relativistic free particle energy has been used directly for the representation of the kinetic energy, and in addition the Darwin term has been included as a correction to the potential energy. This approach can be justified with reference to the Foldy–Wouthuysen reduction of the Dirac equation, but the class of basis functions used in a variational procedure with this Hamiltonian must be restricted to avoid the formation of a node in the wavefunction at the nucleus; the same problem is circumvented in the Cowan–Griffin method by imposing Dirac boundary conditions on the wavefunction. With this method, accurate spin‐orbit splittings have been computed for Br, I, Xe+, CBr, and XeF, but the resulting total energies are found to be overly sensitive to the representation of the inner shells of these systems. Improved results for both valence and inner shells are then shown to follow from the use of the no‐pair equation, which provides a variationally tractable two‐component method employing a momentum dependent potential that gives a realistic description of relativistic effects for atoms and molecules over a suitably large range of Z.
Soliton defects in polyacetylene: Local‐density functional results
Authors: Kutzler F. W. , White C. T. , Mintmire J. W. 
Published: December 2004

AbstractWe report local‐density functional results for the electronic structure of neutral soliton defects in polyacetylene. The results were obtained using a modified version of the discrete variational method Xα molecular cluster model. For defect‐free chains the calculated X‐ray and ultraviolet photoelectron spectra are in good agreement with experiment. For chains with low concentrations of solitons, we find the forbidden gap broadens slightly, and two nearly dispersionless bands, split by several tenths of eV, are introduced into the gap. The predicted splitting is in accord with recent experimental results for this defect.
The omega function for the lithium atom
Authors: Smeyers Yves G. , Delgado‐Barrio G. , Doreste‐Suárez L. , Martin‐González J. M. 
Published: December 2004

AbstractThe omega model is reviewed in the case of a three‐electron function and the omega function determined for the lithium atom ground state by using a procedure based on Brillouin' theorem. The resulting function is analyzed in terms of natural configurations, and the correlation coefficient determined as a function of the distance to the nucleus. It is found that the omega function is essentially equivalent to two configurations built up with the occupied NO' and that the model introduces mainly correlation at large distance. These results contrast with those obtained for the beryllium atom using the same model.