bluuebunny/crossref_metadata_2025 huggingface dataset:
A variational principle for transition and density matrices and approximations to the equations‐of‐motion
Authors: Dmitriev Yuri , Roos Björn
Published: December 2004

A general variational principle for transition and density matrices is proposed. The principle is closely related to Rowe's variational treatment of the equations‐of‐motion method. It permits the simultaneous construction of coupled approximations for two eigenstates, and it is a straightforward extension of the usual variational method.
Generation of genealogical spin eigenfunctions
Authors: Grabenstetter J. E. , Tseng T. J. , Grein F.
Published: December 2004

A method is given for generating the Yamanouchi‐Kotani genealogical spin eigenfunctions which requires neither storage of eigenfunctions for smaller numbers of electrons, nor summations of large order, nor explicit use of results from the theory of representations of the symmetric group. An explicit formula is given for the coefficients of expansion in terms of spin products.
Equivalent spherical harmonics
Authors: Schmelzer A.
Published: December 2004

It is known that the 2l+1 spherical harmonics Ylm can be transformed into cyclically equivalent orbitals, of which only a few examples have so far been given explicitly. In this article the totality of such cyclic sets is derived.

It is demonstrated that other kinds of equivalent spherical harmonics do not exist.

Finally a set of five equivalent d orbitals related to icosahedral symmetry is introduced.
Permutational symmetry of reduced density matrices
Authors: Kryachko Eugene S.
Published: December 2004

The problems of permutational symmetry of the density matrices in reduction are studied. Some necessary and sufficient conditions for N, [λ1], [λ2]‐derivability problem are given.
Uniform quality gaussian basis sets for organo‐silicon compounds
Authors: Mezey P. G. , Yates K. , Theodorakopoulos G. , Csizmadia I. G.
Published: December 2004

By applying the powerful direct optimization technique of conjugate gradients as adapted for the optimization of an open shell energy functional, a uniformly balanced (15s 10p) Gaussian basis set was obtained for the silicon atom. The quality of this basis set, as defined in terms of “exponent forces” or energy gradient |g|, is compatible with the quality of suitably chosen (10s 5p) carbon and (5s) hydrogen basis sets. Contractions better than double zeta were determined for all three bases of Si, C, and H. Using the primitive and contracted bases, ab initio SCF MO calculations were carried out on molecules of SiH4, CH4, and H2. Some of the computed results obtained for H2C = SiH2 are also included as an illustration for organo‐silicon compounds.
Variational localized‐site cluster expansions. VII. Higher ansätze and the linear heisenberg model
Authors: Garcíaa‐bach M. A. , Klein D. J.
Published: December 2004

The localized‐site cluster expansion technique is applied to the infinite linear Heisenberg model with both nearest‐neighbor and next nearest‐neighbor interactions. These cluster ansätze are systematically studied and improved, up to the so‐called 5‐site approximation. Generally we find the present cluster ansätze yield the most accurate variational results yet available.
Electronic structure calculation of [Fe(CN)6]−3 by the SCF‐MSXα method: Study of optical transitions, X‐ray photoelectron spectrum, and Mössbauer isomer shifts
Authors: Guenzburger Diana , Maffeo Bruno , Larsson Sven
Published: December 2004

The SCF‐MSXα method is used to determine the electronic structure of [Fe(CN)6]−3. Optical transition energies and valence electron ionization potentials are calculated and compared with experimental measurements. The electronic charge density at the Fe nucleus is calculated; this result and available electron densities at the Fe nucleus obtained by the same method for other Fe complexes are used to discuss the mechanisms involved in the interpretation of Mössbauer isomer shift values.
Level crossings and branch points studied by the multidimensional partitioning technique
Authors: Brändas Erkki , Froelich Piotr
Published: December 2004

The possibility of level crossings is discussed from a general multidimensional partitioning viewpoint. By extending the traditional motion of a self‐adjoint Hamiltonian to a self‐adjoint analytic family of operators, it is found that level intersections that appear fall into two mutually exclusive categories: the conventional diagonal one corresponding to Jordan blocks of order m = 1, and the nondiagonal one with m ≥ 2. Consequences with respect to some recent examples, such as Longuet‐Higgins “sign‐reversing loop” construction and the 1II near degeneracy in SiO, are discussed and examined.
Additivity model for calculations of UHF spin densities in some aza‐aromatic radical anions
Authors: Sharma K. K.
Published: December 2004

The additivity model suggested by Moss et al. has been applied for predicting spin densities in aza‐aromatic radical anions. The core‐resonance integrals (βrs) have been evaluated using Linderberg's relation. The spin‐density values calculated using the additivity model, have been found to be in good agreement with unrestricted Hartree–Fock (UHF) spin‐density values.
On the approximation of potential‐energy functions for two‐center systems
Authors: Barnsley Michael F. , Aguilar Jacques G.
Published: December 2004

Let E(R) be a potential‐energy function for a neutral or ionic diatom in the Born‐Oppenheimer approximation. Then the approximation of E(R) for 0 < R < ∞ starting from finite and typically small sets of given information is considered. The approach is based on the fact that the scaled potential curves F(R) = R2E(R) derive from an eigenvalue problem which depends linearly on R. The nature of the curves F(R) is examined in detail. The results include the discovery of various approximants, some of which display rigorous bounding properties and others, closely related, whose behavior with respect to the approximated function appears to be predictable.
Intermolecular correlation in a new approximation scheme
Authors: Aronowitz S.
Published: December 2004

It is demonstrated for a spin‐free, nonrelativistic, complete molecular Hamiltonian that there is an optimal solution to the separation of electronic and nuclear motions. The adiabatic approximation is obtained as a special limiting case. A fruitful interpretation of intermolecular correlation results from the assumption that such correlation involves the degeneracy of a molecular‐energy state of one molecule with that of another chemical species, e.g., cubane and cyclooctatetraene. As a consequence, rigorous relationships are established for the influence of nodal patterns of the electronic functions on intermolecular correlation. Also derived are stringent symmetry rules which both electronic and nuclear functions involved in the correlation must obey. Throughout the treatment is a many‐electron one.
Orbital optimization techniques: Comparative study in a semiempirical framework
Authors: Adnan S. S. Z. , Bhattacharya S. , Mukherjee D.
Published: December 2004

In this paper, MC‐SCF and CI methods have been explored for the calculation of ground‐ and excited‐state energies of some aromatic heterocycles in the PPP framework. A new algorithm for solving the orbital equations in MC‐SCF theory has been suggested and its performance has been compared with the conventional gradient optimization technique. Energies of first few transitions have been calculated and compared with rather extensive CI results.
On the adequacy of the molecular‐orbital picture for describing ionization processes
Authors: Cederbaum L. S. , Schirmer J. , Domcke W. , Von Niessen W.
Published: December 2004

General arguments concerning the adequacy of the molecular‐orbital (MO) ionization picture are given. Whereas the MO ionization picture is found to be valid for both outer valence and core electrons, it may completely break down in the inner valence region. The general considerations are supported by many‐body calculations on methane, acetylene, hydrogen cyanide, and dinitrogen tetroxide. It is demonstrated that the breakdown of the MO ionization picture is a common phenomenon.
Conformational analysis of double‐helical polynucleotides
Authors: Khutorsky V. E. , Poltev V. I.
Published: December 2004

The intramolecular interaction energy of the regular double‐helical polynucleotide as a function of variables that determine the mutual position of base pairs and sugar pucker was calculated using atom–atom potentials. The calculations showed the existence of two valley‐like regions with minimal values on the energetic surface. One of them corresponds to the A family of nucleic acids, the other to the B family. The points that correspond to the models constructed by means of x‐ray data are placed in a conformational space near the lines that describe the position of the bottom of the valleys.
Theoretical model study of the reactivity of benzo(a)pyrene diol epoxide with the amino groups of the nucleic acid bases
Authors: Lavery Richard , Pullman Bernard
Published: December 2004

A quantum‐mechanical model study, aided by classical potential calculations, of the formation of adducts between the candidate ultimate carcinogen benzo(a)pyrene diol epoxide and the amino groups of guanine, adenine, and cytosine is presented. An explanation for the preferential reactivity of guanine is proposed and conformational aspects of adduct formation are discussed for both nucleosides and B‐DNA.
Theoretical conformational analysis considering solvent effects
Authors: Hofmann Hans‐Jörg , Peinel Gustav , Weller Thilo
Published: December 2004

The conformational structure of some biologically important compounds (formamide, 1‐methyl‐1,4‐dihydronicotinamide, and chlorocholine) was examined using quantum‐chemical methods. For each of the systems studied a theoretical model (supermolecule approximation, classical continuum model, or hydration shell model) was selected to estimate the influence of solvents on the conformational structure.
Intermolecular interactions of globular proteins in the crystal state
Authors: Makarov A. A. , Monaselidze D. R. , Esipova N. G.
Published: December 2004

The present work is devoted to investigation of thermal transitions in the crystals of seven proteins to compare the protein globule stability in crystal and solution. Calorimetry methods, electron and optical microscopy, as well as x‐ray diffraction studies are used. It is found that protein crystals do not melt and that the destruction of the crystal lattice is a result of protein globule denaturation within the crystal. It is demonstrated that during the heating of pepsin and DF‐trypsin crystals it is possible to observe phase transition of the first order. Equilibrium temperatures of protein denaturation in crystals and in solution coincide. The peculiarities of the crystal state are revealed in the increasing thermal transition cooperativity and the system relaxation period.
Modern state of intermolecular interaction theory
Authors: Kaplan I. G.
Published: December 2004

The concept of potential surfaces and classification of various types of intermolecular forces are given. The possibilities and the criteria of applicability of modern methods for potential surface calculation at short, intermediate, and long distances are discussed. Special attention is paid to the methods for calculating interactions between large molecules.
Molecular orbital study of molecular nitrogen fixation
Authors: Turi Nagy L. , Pelikán P. , Liška M. , Haring M. , Čeppan M. , Breza M.
Published: December 2004

The model systems of molecular nitrogen fixation [N2 + H]⋅, [N2 + H]+, [N2 + H]−, [N2 + H2], [N2 + H2]+, and [N2 + H2]− were studied by the semiempirical INDO method. The study was based on the formal analogy between the catalytic reactions and the photochemical, radical, and ionic reactions on the other side. Symmetrical and donor‐acceptor properties of necessary catalytic systems were proposed using the dependence of energy characteristics and electron structure on reaction coordinate. On the basis of this MO study we have proposed the appropriate symmetry types of catalysts for each of acceptable models of nitrogen fixation. For one of the proposed systems there was realised a model MO computation with explicit inclusion of atoms of transition metals (Fe, V).
Influence of annelation by benzene ring on electronic absorption spectra and on character of the singlet π‐π* transitions at polynuclear p‐quinones
Authors: Nepraš Miloš , Titz Miloš
Published: December 2004

Aromatic polynuclear p‐quinones and their derivatives have been studied using their electronic absorption and luminescence spectra and their basicity. The data were used to provide a basis for the study of the relationships between the structure and the spectral characteristics.
Influence of intermolecular interactions on the DNA conformation
Authors: Malenkov G. G. , Gagua A. V. , Timofeev V. P.
Published: December 2004

Of the two known families of double‐stranded DNA conformations, A is stable in less‐polar, and B in more‐polar solutions. In some water‐nonelectrolyte solutions, B to A transition occurs when water activity in the system is near 0.8. In such systems, however, as water‐methanol, water‐ethylene glycol, etc., B conformation is stable at very low water activity. Hyperfine splitting constant of a spin label (A), a widely used criterion of the solvent polarity, was measured by EPR method in the solutions, in which B to A transition takes place at 25°C. A values in solutions of different compositions are close to each other. A method for quantitative estimation of Van der Waals and hydrogen‐bond contributions to A values is proposed. A values in water‐methanol solutions show that their polarity is too high for the A form to be stable. Decreasing temperature shifts the B‐A equilibrium to the B form, which correlates with increasing polarity of the water‐alcohol solutions, as measured by the EPR method. Thus B to A transition is mainly determined by the polarity of the environment, which, in turn, is determined by the ability of the solvent molecules to participate in Van der Waals interactions and hydrogen bonding.
Bose condensation of phonons in biological systems
Authors: Moskalenko S. A. , Pokatilov E. P. , Miglei M. F. , Kiselyova E. S.
Published: December 2004

Using the Bogolyubov's rate equation from the theory of superfluidity the possibility of Bose condensation of phonons in biological systems and the validity of Fröhlich's hypothesis has been proved. We took into account both the third and the fourth anharmonism in the rate equation. All the processes with active phonons (from one to four) of biological active modes have been investigated. Taking into account these processes the expression for the chemical potential is shown to be changed, but the conditions for Bose condensation of phonons still exist. For the first time we point out the possibility of soliton wave packet propagation in the coherent systems of phonons and photons. The possibility of Bose condensation of excitons in biological systems is also discussed.
Modeling of the short‐range order for polymers by the ideal peak method
Authors: Shilov V. V. , Kruglyak N. E. , Lipatov Yu. S.
Published: December 2004

The method of the modeling of the radial distribution function for liquid and amorphous polymers is described. The method consists in the use of pair functions of the radial distribution (ideal peaks) for the construction of the distribution function of intramolecular distances and the comparison of the theoretical function with the experimental one. The theoretical functions for two possible conformations of the poly(tetramethylene glycol) macromolecule were computed. It follows from comparison of the computed theoretical functions with the experimental one that the intramolecular distances do not become apparent in the experimental curve. The differential functions containing the contributions of the intermolecular distances only were obtained by subtraction of the theoretical function from the experimental. Comparison of the differential functions of the two conformational states which were taken as models proved that there are large numbers of gauche conformations in the liquid polymer in contrast to the crystalline polymer. On the basis of the analysis of the differential functions for liquid and crystalline poly(tetramethylene glycol), we concluded that the short‐range order of the polymer is distorted during the melting in that the basic plane of the poly(tetramethylene glycol) paracrystal becomes almost hexagonal.
Theoretical study of electronic spectra of the DNA bases
Authors: Kuprievich V. A. , Shramko O. V.
Published: December 2004

Excited π‐electronic states of cytosine and uracil are calculated by the CI method. The effects of a transition from the single‐excited configuration set to the set involving all double‐excited configurations are considered. The set expansion is shown to affect essentially the transition energies and oscillator strengths, in particular, an additional electron transition related to the first absorption band occurs in the singlet uracil spectrum. When doubly excitations are taken into account the triplet transition energies considerably increase and become practically insensitive to repulsion integral parametrization.
Solvation of nonpolar groups of biomacromolecules
Authors: Sarkisov G. N. , Agrafonov Yu. V. , Martynov G. A.
Published: December 2004

The method of correlation functions used in the theory of liquids is suggested for investigation of the solvation shell structure in the vicinity of nonpolar surfaces. An approach making it possible to obtain the molecule correlation functions in the solvation shell is worked out. In this approach the correlation functions are the product of the interatomic correlation functions.
Effective utilization of off‐diagonal hypervirial relations considering diagonal hypervirial relation: Harmonic oscillator case
Authors: Sakamoto Kazuyoshi , Terasaka Toshitaka
Published: December 2004

The effective utilization of hypervirial relations is scrutinized to improve the approximate excited‐state functions in the harmonic oscillator system. A new method is presented which simultaneously employs the off‐diagonal hypervirial relations with the diagonal hypervirial relation. In order to use these relations effectively, the following points are pointed out: (i) the presented method is useful to get better reasonable results for the excitation energies and the state functions; (ii) the ground state given must satisfy the virial theorem; (iii) in the hypervirial operator used here as xm, the smaller integers of m's present better results; and (iv) the employment of the comparatively small number of trial basis functions of the type exp (−γ|x|) is sufficient for reproducing the exact excited state. Especially among them, condition (ii) plays an important role. Applying all the proposals to the first and the second excited states, one gets a highly improved excitation energy, state function, and other physical quantities (e.g., transition moment and oscillator strength). The presented method is also found to be more effective than the employment of only the off‐diagonal hypervirial relations or the method of the scaling operation.
Second quantization for composite particles, reactive collisions, and unstable particles
Authors: Girardeau M. D.
Published: December 2004

The salient features of generalized second‐quantization representations for nonrelativistic systems of composite particles are reviewed and their application to a reformulation of the quantum theory of reactive collisions is discussed. Such representations allow the properties of the bound composite states to be built explicitly into the algebra of states and observables. A single unperturbed Hamiltonian simultaneously describes the free propagation of the various species of bound composites as well as of their unbound constituents, while the interaction Hamiltonian describes only true scattering and reaction processes. The inclusion of the binding of all composites in the unperturbed Hamiltonian cures the divergences in the Born series arising from bound‐state poles. Unstable composites can be included in a natural way, leading to an explicit representation for the kinematics and dynamics of their decay and their contribution to collision phenomena.
Quantum‐field theory and electrodynamics of superconducting systems
Authors: Fusco‐Girard M. , Mancini F. , Marinaro M.
Published: December 2004

By using quantum‐field theory techniques and the boson transformation method, we study systems that exhibit macroscopic ordered states. As an illustration, we apply the method to the study of superconducting systems by taking into account the quantization of the vector potential. The results of a dynamical calculation, performed in the pair approximation, are presented. The Higgs phenomenon is also discussed in the framework of a fully quantum theory.
Fiber bundles, sheaf theory, and generalization of differentiable manifolds in physics
Authors: Chow Yutze
Published: December 2004

Some aspects of fiber bundles, sheaf theory, and possible generalizations of the notion of differentiable manifolds are discussed.
Irreversibility, decay, and asymptotic dynamics
Authors: Emch Gérard G.
Published: December 2004

This paper contains the skeleton of one lecture, and of two raporteur's interventions, made at the Sanibel Symposium in February–March, 1979. The task asked of this lecturer was to present an outline of the program of nonequilibrium statistical mechanics, and to indicate some of the recent developments in our understanding of this program. Section I lists a few of the principal physical ingredients of the theory. The possible implementation of certain aspects of the program is demonstrated in Sec. II with the help of three exactly soluble models. Finally in Sec. III we extrapolate from these particular examples in two directions: the stochastic aspect of statistical mechanics, and some remarks on the theory of the quantum measurement process. The presence, at the Symposium, of several distinguished lecturers who presented their own original, and most interesting, contributions hopefully made appear less outrageous—at least at the time—the severe omissions due to the personal choices this particular speaker had to make to keep within the time limitations inherent to such a gathering. It is now hoped that, even when taken out of the full context of the Symposium, the rearranged text which follows might nevertheless help focusing attention on some of the important problems remaining to be solved. It is a pleasure to acknowledge here the stimulating hospitality of the Symposium Scientific Director, Professor P.‐O. Löwdin.
Nodeless wave function quantum theory
Authors: Hunter Geoffrey
Published: December 2004

The nodes where the wave function changes sign in conventional quantum theory can alternatively be regarded as places where the wave function descends to zero but rises again without changing its sign. This behavior is accomplished by adding delta function barriers to the potential energy wherever a node occurs in the wave function. This model is supported by the recognition that the wave functions of a subsystem, which is not truly isolated, are really marginal amplitudes which implicitly average out interactions of the system with its environment. The finite effect of these interactions is to replace the delta function barriers by barriers of finite width and height.
Variation principle for the time dependence of density operators and its relation to linear decoupling procedures for propagators
Authors: Dalgaard Esper
Published: December 2004

A modified form of Frenkel's time‐dependent variation principle, suggested by McLachlan for state vectors, is employed to discuss the optimal time evolution of a density operator ρ(t). An ansatz is made for this operator such that i(dρ/dt) = [S, ρ], where S(t) is a linear combination of operators belonging to a particular manifold of “basis operators.” The expansion coefficients are required to minimize the error Tr{[S – H, ρ]† [S – H, ρ]}. Linear response functions corresponding to the variationally determined density operator are compared to those derived by means of linear decoupling procedures for propagators based on the same operator manifold. The two approximation schemes are not equivalent, in general, and several consistency requirements must be fulfilled before it can be ascertained that a given linear decoupling procedure corresponds to an optimal time development of the density operator in the sense of McLachlan. Finally, the general applicability of the suggested variation principle is discussed.
Equations de Hartree–Fock dependant du temps
Authors: Smet F. , Tillieu J. , Van Groenendael Et A.
Published: December 2004

The time‐dependent Hartree–Fock (TDHF) equations are derived up to the second order when the system is perturbed by a monochromatic plane wave. The solutions of the equations are subjected to the orthonormalization conditions satisfied by the orbitals. In the equations, these conditions are expressed by the appearing of coefficients λ playing the part of Lagrangian multipliers. Relations between the coefficients λ are established. These relations are equivalent to the above‐mentioned orthonormalization conditions. This equivalence enables us to substitute for the solution of an integrodifferential equation system subject to constraint conditions, that of a free system. The TDHF equations obtained determine the first‐ and second‐order orbital perturbations, which no doubt verify the orthonormalization conditions. These orbitals can be used in the calculation, up to second order, of different nonlinear optical effects.
Effect of side‐chain disorder on the electronic structure of proteins
Authors: Suhai Sándor , Kaspar Johannes , Ladik János
Published: December 2004

The influence of side‐chain disorder on the electronic structure of proteins has been investigated in the case of polypeptides containing two or three different amino acid residues. It has been found that due to the different potentials of different side‐chain groups, the original valence and conduction bands of the homopolypeptides are split into narrow bands. The comparison of the densities of electronic states in simple homopolypeptides and in composite polymers shows that new forbidden regions in the energy spectrum of proteins may develop. The consequences of these effects for the semiconductive properties of proteins are discussed.
Criteria of accuracy of resonance eigenvalues
Authors: Moiseyev Nimrod , Weinhold Frank
Published: December 2004

Various criteria that have been suggested for assessing the accuracy of complex‐coordinate eigenvalues are critically tested in an application to the lowest helium 1S resonance, and found to be relatively ineffective. An alternative criterion is described, based on a generalized stabilization procedure, which seems better able to select the “best” resonance eigenvalue and to guide the construction of variational trial functions.
Effect of symmetry lowering on the band structure of polyacetylene
Authors: Morton‐Blake D. A.
Published: December 2004

In an attempt to apply band‐structure calculations to polymers with “reduced” symmetries, and simultaneously to examine some of the causes of band gaps in semiconducting polymers, two types of symmetry reduction are applied on the all‐trans polyacetylene chain. Using a neighboring‐segment approximation the consequent perturbations were used to calculate changes to the band structure of the undistorted chain and the energy gaps compared with those obtained from a direct calculation on the distorted polymer.
Hydrogenic orbitals as minimum‐basis functions for SCF calculations
Authors: Boerth Donald W. , Van‐Catledge F. A.
Published: December 2004

The orbital approximation that polyelectronic atoms can be qualitatively described by using hydrogenlike orbitals was tested quantitatively. Hydrogenic atomic orbitals (HTO's) were investigated as best‐atom minimum‐basis set functions and were compared to best‐atom Slater orbitals (STO's). The two sets of wave functions were compared in terms of the ground‐state energies, the electron densities at the nuclei, charge distribution in space, electron populations, and atomic “radii.” In the atomic calculations the HTO's give somewhat poorer atom descriptions that STO's. SCF calculations on diatomic molecules (N2, CO, and HF) indicate that while HTO's give higher molecular energies, they closely mimic STO's in terms of electronic reorganization. The principal difference between HTO and STO results was attributed to the compact nature of the HTO 2s orbital.
Toward a very simple picture of disorder effects in one‐dimensional organic conductors
Authors: Dugay M. , Roustan J.
Published: December 2004

We present a simple model for the calculation of some properties of disordered one‐dimensional organic conductors. We focus our attention on two points: the decrease of the insulator‐to‐metal transition temperature and the increase of the highest electrical conductivity temperature that both occur when the amount of disorder is increased. We give an explanation that brings a new insight to the still little understood zone around the insulator‐to‐metal transition. The model enters the general framework of the alternant molecular orbital method and seems to be a priori restricted to systems such as NMP‐TCNQ. We discuss its possible application to more complicated systems such as TTF‐TCNQ.
Degenerate symmetry‐adapted perturbation theory. Convergence properties of perturbation expansions for excited states of H2+ ion
Authors: Chałasińaski Grezegorz , Szalewicz Krzysztof
Published: December 2004

The degenerate Rayleigh‐Schrödinger (RS), Murrell–Shaw–Musher–Amos (MSMA), and Eisenschitz–London—Hirschfelder–van der Avoird (EL–HAV) perturbation theories are formulated and applied through high order to the interaction of a hydrogen atom with a proton for the excited 2sσg, 3pσu, 3dσg, and 4fσu states of the system. In contrast to the 1sσg and 2pσu states all the formalisms fail to provide a convergent series for any of the above states. However, numerical evidence is given that for sufficiently large internuclear separations the RS series is able to reproduce the Coulomb energy with an accuracy better than an arbitrary fraction of the exchange energy. Similarly the exchange energy can be reproduced by the sum of a few exchange corrections of the MSMA method. It has also been shown that both the MSMA and EL–HAV series can be continued analytically beyond the convergence radius by means of Padé approximants.
Concept of charge transfer: Investigation of charge transfer in the glyoxal–formamide, water dimer, and water–lithium cation systems
Authors: Otto P. , Ladik J.
Published: December 2004

In this paper an attempt is made to define charge transfer trying also other ways than Mulliken's population analysis. To illustrate this the amount of transferred charge (q) in the complexes HCONH2 + OHC—CHO in two relative geometrical positions, H2O + H2O and H2O + Li+ has been calculated with the help of Mulliken's population analysis using the wave function of the complex on the one hand and in the framework of different methods to subdivide the total space of the complex into subspaces for the acceptor and donor molecule, respectively, on the other hand. The results obtained show that Mulliken's population analysis gives a qualitatively correct description of the charge transfer process but to obtain the finer details most probably the use of a single number (q) is not sufficient. Further, the change in the total energy with respect to an effective charge transfer of a water dimer and of a solvent–cation complex has been investigated using the new mutually consistent field method. In this way the amount of transferred charge as well as the charge transfer interaction energy have been obtained in one step. These results have been compared with calculations applying second‐order perturbation theory including overlap and the supermolecule method.
Molecular‐orbital treatment of complex cations of magnesium and beryllium with acetonitrile
Authors: Morton‐Blake D. A. , Russell N. R.
Published: December 2004

Semiempirical MO calculations of the self‐consistent charge and configuration (SCCC) method are reported for the acetonitrile–metal solvated species (CH3CN)xMn+, where M = Be2+ and Mg2+. Comparison of the delocalization energies for various chemical structures x = 1, 2, 3, 4, 6 leads to an expectation of a tetrahedral structure for the Be2+ species and an octahedral structure for the Mg2+ species. The electronic nature of the donor–acceptor interaction is also discussed.
Variation of calculated single bond lengths in saturated hydrocarbon and silicon hydride molecules
Authors: Verwoerd W. S.
Published: December 2004

A series of saturated XnHm (X being either C or Si) molecules is studied using the MINDO/3 and MNDO quantum‐chemistry procedures. We find that the proximity of H atoms tends to shorten XX bonds, and that this effect is (especially for MINDO/3) much larger than a similar trend in experimental values. The connection between this and hybridization values calculated from localized orbitals is investigated. It is found that the hybridization model works well for XH bonds, whereas for XX bonds non‐σ‐bond effects also play a significant role. It is shown that the changes in electronic structure may be directly connected to differences in X and H atomic levels, so that similar bond length differences may be expected in other molecular orbital calculations.
Model for the lipid monolayer‐phase transitions
Authors: Maekawa Hiroyuki , Hosokawa Masahiko
Published: December 2004

A theoretical order–disorder model for the main phase transition of lipid monolayers is presented here. The model contains approximate treatments of hard‐core repulsions and attractive forces between molecules. The lipid molecules are assumed as the square plates and then the entropy of the configurations is obtained using the placement method in a two‐dimensional lattice. The approximation used to compute the thermodynamic behavior of the model turns out to be a kind of molecular‐field approximation. The resultant pressure–density isotherms for the three‐state model show the characteristic van der Waals loops.
Electrical and thermal properties of the partially oxidized salt of the magnus green salt with the formula Pt6 (NH3)10Cl10(HSO4)4
Authors: Kubota R. , Kobayashi H. , Tsujikawa I. , Enoki T.
Published: December 2004

The salt Pt6(NH3)10Cl10(HSO4)4(MGSPOS) with the average valence of Pt 2.33 was prepared in powder form by means of partial oxidization of [Pt(NH3)4][PtCl4](MGS) substituting HSO4− for 1/6 of both ligands NH3 and Cl−. The electrical conductivity σ has a maximum at about 230 K and a minimum at about 280 K. Therefore, the conductivity σ is semiconductive with the gap energy 0.04 eV below 230 K, and metallic in the sense of dσ/dT < 0 between 230 and 280 K, and again semiconductive above 280 K. The thermal analysis by DSC shows only on heating, three anomalies, G at ∼150 K, A at ∼ 200 K, and B at ∼250 K. The exothermic anomaly A succeeding to the weak anomaly G indicates that a glass transition takes place, and endothermic anomaly B corresponds to a structural transition. These two transitions may correspond to the two metal–semiconductor transitions found in the σ measurement. The ac calorimetry shows a specific heat anomaly also only on heating.
Use of noncanonical orbitals in many‐body perturbation theory
Authors: McDowell Keith
Published: December 2004

A formalism for dealing with noncanonical Hartree–Fock spin orbitals is presented within the framework of many‐body perturbation theory. A test calculation on the planar methyl radical is carried out which displays certain features of open‐shell calculations and which demonstrates the viability of using noncanonical spin orbitals. Results are found to be in good agreement with a previous configuration interaction calculation.
Static dipole and quadrupole polarizabilities of alkaline earth atoms
Authors: Sen K. D. , Schmidt P. C.
Published: December 2004

Static dipole and quadrupole polarizability (αd and αq, respectively) values of coupled Hartree–Fock quality have been calculated for the alkaline earth atoms Be(2s), Mg(3s), Ca(4s), and Sr(5s) using a method based on the many‐body perturbation theory. The present values of αd and αq for Be and αd for Mg are in excellent agreement with the other available results of similar accuracy. The CHF calculations of αd for Sr and αq for Mg, Ca, and Sr are being reported for the first time.
Suitability of a square step potential as an oscillator potential
Authors: Gustav Klaus , Colditz Roland
Published: December 2004

The time‐independent Schrödinger equation for a one‐dimensional square step potential with impenetrable walls was solved to prove the suitability as an oscillator potential. The mathematical structure of the eigenvalue conditions and the number of eigenstates within one potential step are discussed.
Binding: A unifying notion or a pseudoconcept?
Authors: Del Re Giuseppe
Published: December 2004

Communication between chemists and physicists working in different domains of physical chemistry may sound like a dream, but actually it must be established in order that the whole field may develop in a more efficient way. Binding is a unifying concept whose discussion may make it possible for specialists of different extractions to profit from each other's work. When different specialists speak of binding, they have some intuitive picture in mind. Does it correspond to a unique well‐defined concept, or is it just a cover for ignorance? A tentative definition is proposed as a starting point for discussion, but it is also emphasized that only from an open‐minded and thorough analysis of the various interpretations it should be possible to make real progress. An example showing very clearly the relationship between the various topics is that of biopolymers, whose understanding depends on the specification of the role of a variety of binding effects, from chemisorption to charge transfer to (one‐dimensional) metallic binding.
“Binding” technology and fundamental research: Some cases in catalysis
Authors: Ciambelli Paolo
Published: December 2004

The point of view of chemical engineers concerning the possible contributions of fundamental research to their work is briefly illustrated by reference to catalyst design. Specific questions on which the author is working are mentioned. The growing importance of zeolites and their challenge for fundamental research is also pointed out.
Experimental evidence on the chemisorption bond with the chemisorption on metals
Authors: Wedler G.
Published: December 2004

Which information on the properties of the adsorption complex can be obtained from the application of the standard methods in experimental surface science is discussed. None of the methods gives all the information necessary for a complete description of the chemisorption bond so that the results delivered by as many methods as possible should be taken into account.
Metal clusters and surfaces
Authors: Borello E.
Published: December 2004

The point of view of a physical chemist interested in metal clusters because of their connection with heterogeneous catalysis is illustrated. The analogies and differences between clusters and surfaces are given special attention. After a review of experimental techniques and of types of clusters studied, very important questions of theory are briefly considered, with special reference to Lauher's rules for predicting the stoichiometry of clusters. The relevance of clusters to surface studies is discussed also with reference to fluxionality and reactivity.
Matrix isolated clusters and microcrystals
Authors: Martin T. P.
Published: December 2004

After emphasizing the importance of absorption spectra of metal clusters, with special reference to alkali halide IR absorption, the equilibrium configurations and the binding energies of alkali halide clusters are discussed in terms of a very simple two‐body interaction.
Correlations between structure and properties of materials. X. Anomalous optical properties and Raman spectra of glassy ternary B2O3–BaTiO3–Na2O materials
Authors: Bertoluzza A. , Marinangeli A. , Morelli M. A. , Simoni R.
Published: December 2004

The anomalous behavior of refractive index and density in the glassy ternary B2O3–BaTiO3–Na2O materials is presented and discussed in terms of Raman spectroscopy results. The slope change in the optical properties as a function of composition takes place within the same range of composition in which the Raman spectra suggest a transition from a bridging type of attack on the glassy matrix by the oxygen present in the basic oxide, to a nonbridging type. The structural modifications of the materials at different compositions are inferred from a detailed analysis of the Raman spectra.
Binding of leucomycin and its derivatives to E. Coli ribosomes
Authors: Jain D. V. S. , Gombar Vijay
Published: December 2004

Structure‐activity relationships have been discussed for inhibition of [14C] erythromycin binding to Escherichia coli ribosomes by leucomycin and its acyl derivatives in the light of the Fujita‐Ban de novo model. The group contributions of various substituents show that acylation at position 4″ of the mycarose moiety of leucomycin increases affinity for binding of leucomycins to ribosomes. It is also indicated that unlike at position 2' in mycaminose region a free hydroxyl at position 9 of the lactone ring is not important for binding to ribosomes.
Cytochrome c: Ascorbate reduction site and possible electron‐transfer path
Authors: Myer Yash P. , Pande A. , Pande J. , Thallam K. K. , Saturno A. F. , Verma Balbir C.
Published: December 2004

The ascorbate reduction reaction of the native and urea‐perturbed forms, 0–8M urea, of horse heart ferricytochrome c is found to be a three‐step process: a urea‐dependent equilibrium step between a reducible and an irreducible form with a midconcentration of urea of 7.4M, a binding step with a binding constant of 5.9M–1, and a reduction step with a urea‐independent rate constant of 2.9 ± 0.3 s–1 [J. Biol. Chem. 255, 9666 (1980)]. The effect of adding urea, in addition to the generation of an irreducible form, is a slight lowering of the ascorbate‐protein binding constant, 5.9 to 2.7M–1, which is limited to the 0–5.5M concentration range. The thermodynamics of the ureadenaturation process also yields a three‐step mechanism, NX1X2D, with midconcentrations of urea of 2.5–3M, 6.2M, and 7.5M, respectively, where N, D, and the Xs are the native, the 9‐M‐urea, and the intermediate forms. The three processes are described as the loosening of the heme crevice opening, the solvent exposure of the polypeptide backbone, and the disruption of the tryptophan–porphyrin interactions, respectively [Biochemistry 19, 199 (1980)]. The reaction of the protein with 2,3‐butanedione, a group‐specific reagent for the guanidinium groups and an electron donor for this protein, is inhibited in the presence of ascorbate, but only one of the two functional groups is involved [J. Biol. Chem. 255, 11094 (1980)]. A correlation of kinetic and thermodynamic observations led to the conclusion that the ascorbate reduction of the protein is independent of the state of the heme crevice opening and of the polypeptide organized structures; instead, it is determined by the integrity of the tryptophan indole–porphyrin interactions. This information, when taken in conjunction with the selective inhibition of the reaction of the arginine side chains by ascorbate, establishes the binding site of ascrobate as one of the two arginyl side chains, and not the opening of the crevice or its vicinity. From the three‐dimensional structure of the protein, and taking into consideration the variability of the protein sequence, it is suggested that Arg‐38 is the ascorbate binding site, and that the electronic interaction between the indole of Trp‐59 and the porphyrin moiety must constitute, at least in part, the electron‐transfer path to heme iron.
Electron impact excitation cross sections for O II
Authors: Ganas P. S.
Published: December 2004

Generalized oscillator strengths and integrated cross sections from threshold to 1 keV are calculated in the Born approximation for the electron impact excitation of O II.
Ordered products of exponential operators by similarity transformations
Authors: Witschel W.
Published: December 2004

The well‐known Hausdorff similarity transformation is used to derive a number of identities for exponential operators. The method does not give new results, but is shown to be a simple alternative to Feynman disentangling, parameter differentiation–differential equation, coherent states, and Lie–algebraic‐matrix techniques.
Large‐Order perturbation theory
Authors: Wu Tai Tsun
Published: December 2004

The original motivation for studying the asymptotic behavior of the coefficients of perturbation series came from quantum field theory. An overview is given of some of the attempts to understand quantum field theory beyond finite‐order perturbation series. At least in the case of the Thirring model and probably in general, the full content of a relativistic quantum field theory cannot be recovered from its perturbation series. This difficulty, however, does not occur in quantum mechanics, and the anharmonic oscillator is used to illustrate the methods used in large‐order perturbation theory. Two completely different methods are discussed, the first one using the WKB approximation, and a second one involving the statistical analysis of Feynman diagrams. The first one is well developed and gives detailed information about the desired asymptotic behavior, while the second one is still in its infancy and gives instead information about the distribution of vertices of the Feynman diagrams.
Is quantum chemistry concerned with materials science?
Authors: Calais Jean‐Louis
Published: December 2004

The reasons for the surprisingly little contact between quantum chemists and materials scientists are discussed. Examples of areas where such contacts could be very beneficial are given.
Converging SCF calculations on excited states
Authors: De Mello P. Corrêa , Hehenberger M. , Zernert M. C.
Published: December 2004

A practical scheme for the calculation of excited states of the same symmetry as a given reference state is outlined in the context of the Hartree‐Fock method. In order to prevent the excited state from “collapsing” into a lower‐lying state, the prediagonalized Fock matrix is diagonalized in a restricted subspace, deleting the component associated with the orbital which participates in the excitation. Computationally, the deletion is accomplished by means of a “big shift” of the associated diagonal element of the prediagonalized Fock matrix. The resulting wave function will not be fully relaxed, but can be shown to be orthogonal to the reference state. The method has been implemented in a molecular UHF program. Applications to the 4σ hole state of CO and to an excited state of the CuCl ion are reported.
Symmetry groups of chemical graphs
Authors: Balasubramanian K.
Published: December 2004

The symmetry groups of all trees are shown to be expressible as generalized wreath products by a tree pruning algorithm. The symmetry groups of certain cyclic graphs which can be expresssed as generalized compositions are also shown to be generalized wreath products. The symmetry groups of complete multipartite graphs can be obtained in a similar manner. Character tables of symmetry groups of certain chemical graphs are also obtained.
Ab initio calculations of the electronic structures of Dimethylnitrosamine (DMN) and its Metabolite Hydroxydimethylnitrosamine (HDMN): A possible intermediate in carcinogenesis by DMN
Authors: Skancke Anne , Thomson Colin
Published: December 2004

The structure of N,N'‐dimethylnitrosamine (DMN) and its α‐hydroxy derivative have been computed using the ab initio force method with a 4‐21 basis set. The results are compared with experiment for DMN.