bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemische Umwandlungen. XXVII [1]. Ein «stabiles» Benzoloxid Vorläufige Mitteilung
Authors: Prinzbach H. , Vogel P.
Published: December 2004

By thermal isomerization of the 3‐oxa‐6.7‐diphenyl‐tetracyclo [3.2.0.02, 7. 04, 6]‐heptane‐1. 5‐dicarbomethoxylate (4) besides the oxanorbornadiene 3 and the hydroxy‐fulvene 7, the ‘stable’ benzeneoxide 7‐oxa‐2.5‐diphenyl‐bicyclo [4.1.0] hepta‐2.4‐diene‐3.4‐dicarbomethoxylate (5) has been isolated. In the temperature range −50 to 170°C no equilibration with the monocyclic oxepine 6 has been detected.
Free‐electron model and triplet‐state lifetime of benzene
Authors: Sen Purnendranath , Basu Sadhan
Published: December 2004

Using the free‐electron model the triplet‐state lifetime of benzene for the 330 mμ band has been estimated to be about 36 sec, which compares favourably with the corrected experimental value of 30 sec. It has also been established that the perturbing singlet must be a π‐σ singlet rather than a π‐π singlet.
Localized impurity states in the Hartree‐Fock, LCAO approximation. I.
Authors: Martino F.
Published: December 2004

One‐electron energies and wave functions for deep trap impurity electrons in a crystal are calculated by the Hartree‐Fock, single determinant method. The interactions arising from a many‐electron single determinant crystal wave function, with automatic inclusion of exchange effects, are those which determine the one‐electron functions and energies. The crystal plus impurity system has no translational symmetry and hence the Bloch theorem is not applicable for the solution of the essentially infinite Hartree‐Fock eigenvalue matrix. Thus we develop a technique in which the Hamiltonian and overlap matrices are written in terms of bordered matrices, with the interaction of the impurity functions with the rest of the crystal environment contained in the bordering rows and columns. The resulting secular equation explicitly includes the effects of orthogonalization of the entire basis set, including the impurity functions. This technique could be used in an iterative calculation of the electronic structure of a small number of electrons, assuming that the rest of the electrons in the environment are fixed according to an initial estimate.
Inelastic molecular collisions with an orientation‐averaged interaction energy
Authors: Shin Hyung Kyu
Published: December 2004

The importance of molecular orientations for vibrational‐translational energy transfers between diatomic molecules has been investigated. An angle‐dependent potential function is assumed, and it is averaged over the orientations and vibrations of colliding molecules. For I2I2 and Cl2Cl2, it is found that the calculated average vibrational transition probability for a colinear collision is over‐estimated by large factors (1/γ) compared to that obtained when all possible molecular orientations are considered. At 3000K, 1/γ = 34.4 for I2I2 and 17.6 for Cl2Cl2, while it is 6.8 and 5.9 for N2N2 and O22, respectively. It is also shown that 1/γ decreases rapidly as temperature increases. At 20000K, 1/γ ≈︂ 3 for I2I2, Cl2Cl2, and N2N2, while it is ≈︂ 2.5 for O2O2. In general, when the molecules are large, and when strong attractive forces act between them, 1/γ is very large at low temperatures (<10000K).
Electronic structures and spectra of halogenated purines and pyrimidines II.π‐Electronic structure of 2‐chloropurine and its related derivatives
Authors: Song Pill‐Soon
Published: December 2004

Electronic structures and spectra of “non‐alternant” heterocyclic 2‐chloropurine and its analogs have been computed with different MO techniques, namely, HMO, ω‐SCF‐HMO (ω = 1.4 and 0.5), and PPP semiempirical SCF‐ASMO‐CI. Triplet‐state energies have been calculated by the last method. In general, it is found that at least semiquantitatively consistent results on the ground‐state properties of the molecules are obtained from the different MO methods. As expected, excited states of the molecules are not satisfactorily treated by the HMO and σ techniques. However, an excellent agreement between the observed and calculated π‐π* transition energies has been obtained with the PPP method. In view of the semiquantitative consistency of the ground‐state properties, the use of simple methods such as HMO and ω(=0.5)‐SCF techniques is justifiable for limited application to molecular biology.

Results on the molecular geometry, dipole moments, ionization potentials, xanthine oxidase reactivity and spectra have been discussed with regard to the halogen substitutions in the purine base. The significance of these results with reference to the biological uses of substituted purines is briefly described.
Exposé d'une méthode de détermination des orbitales virtuelles pour les interactions de configurations. Application à l'etat fondamental de l'atome de béryllium
Authors: Leclercq J. ‐M.
Published: December 2004

A method for the determination of the virtual orbitals for configuration interaction is described. This method is a generalization of the one used by Watson in 1960 for the ground state of the beryllium atom. The important point in the method is to complete the set of functions used successively. As an illustration the method is applied to the ground state of the beryllium atom. The method seems to be efficient.
Configuration interaction study of H2 and H3 systems
Authors: Gianinetti E. , Majorino G. F. , Rusconi E. , Simonetta M.
Published: December 2004

The configuration interaction method has been applied to the H2 and H3 systems. The effect of increasing the size of the atomic Slater‐type orbital basis has been studied. A minimization procedure with respect to orbital exponents has been carried out.
Zur konstruktion von energiehyperflächen
Authors: Preuss H.
Published: December 2004

An analytical approximation for the hypersurface ℰ (pr‐approximation) is given using the two‐ and three‐center‐functions pλμ and r, which is valid for any number N of atoms and is invariant with respect to the number of centers in its analytical structure (rule of construction). This is valid too if N is reduced either by the association of atoms or by transitions to infinity. pλμ can be fixed by two‐center‐systems. But r is still free except for the fulfilling of some simple requirements. The rule of construction proposed for ℰ is an example for using so‐called analytical computers.
Group theory and reaction mechanisms: Permutation theoretic prediction and computational support for pseudorotation modes in C2H and C5H rearrangements
Authors: Bouman Thomas D. , Duncan Charles D. , Trindle Carl
Published: December 2004

The McIver–Stanton rules concerning the symmetry of transition states have a counterpart in rules concerning the permutation symmetry of single steps in degenerate rearrangements, derivable with the aid of Longuet–Higgins group theory. The generalized rules are illustrated by the widely studied PX5 polytopal rearrangements. The analysis leads to prediction of hitherto unexplored “pseudorotation” pathways for rearrangements in ethyl and homotetrahedryl cations. CNDO computations of system energies, gradients, and curvatures at critical points on the C2H and C5H surfaces indicate that symmetry‐breaking in keeping with the permutation‐theoretic predictions is a key feature of the low‐energy rearrangements of these systems. In particular, computation indicates that the C2v “classical” homotetrahedral cation corresponds to an energy maximum rather than an energy minimum, or a transition state.
Matrix elements and their selection rules from ladder operator considerations
Authors: Hadinger G. , Bessis N. , Bessis G.
Published: December 2004

Within the Schrödinger–Infeld–Hull factorization framework it is shown that, by introducing a parameter ε in the quantization condition, that is, ε(j–|m|)=integer ≥ 0, and, thus, considering “symmetrized” ladder operators, one can use the same formulas to handle both class I (ε = +1) and class II (ε = −1) problems. Starting from this unified point of view, after building up the associated angular momentum operators and their ε‐dependent eigenfunctions, one unique closed‐form expression of the coupling coefficients is obtained. This expression embodies many sparse and known previous results, without being more intricate than any of them. The basic material, allowing the application of a Wignera–Eckart theorem to matrix elements of an operator on the basis of eigenfunctions of factorizable equations, and a quick determination of the associated selection rules are given. Some examples are treated as an illustration.
Determination of excitation energies and transition moments in a second order polarization propagator approach. Application to the Be atom and the CH+ molecule
Authors: Oddershede Jens , Jørgensen Poul , Beebe Nelson H. F.
Published: December 2004

Excitation energies and transition moments have been determined from a second order polarization propagator and the effect of including energy shifted denominators has been investigated. Results for Be and CH+ show a change of 2–5% for the transition moments and of 0–20% for the singlet excitation energies in a second order approach compared to a first order (time‐dependent Hartree‐Fock) approximation. Both Be and CH+ are triplet unstable in the time‐dependent Hartree‐Fock approximation. The triplet instability is removed for Be but not for CH+ in a second order polarization propagator approach.
The physics of the born–oppenheimer approximation
Authors: Essén H.
Published: December 2004

A new derivation of the Born–Oppenheimer separation of electronic and nuclear motion is presented. The arguments used differ from those in earlier works in not being specially designed for molecules. Instead they aim at an intuitive understanding of the qualitative behavior of the low energy bound states of any, real or hypothetical, Coulomb interacting system of particles. The virial theorem is the starting point of the discussion. After a brief explanation of how it can be used to understand atomic structure it is applied to molecules. It is found that coordinates of collective and individual motion are natural coordinates for the approximate separation, rather than nuclear and electronic. It is also shown that it is the form of the interaction between the particles that is responsible for the separation; the smallness of met/MNu is irrelevant.
Problems of the calculation of intermolecular interactions on complexes with strong delocalized π‐bonds within the PCILO framework
Authors: Lochmann R.
Published: December 2004

Strong delocalized π‐bonds must be approximated by localized π‐bonds within the PCILO framework. From this approximation some difficulties result in the calculation of intermolecular interactions. If only one subsystem involves delocalized π‐bonds the difficulties seem to be not very important. But if both subsystems involve such bonds, the PCILO results are not reasonable in some cases.
Calculation of molecular crystals within the PCILOCC framework
Authors: Lochmann R.
Published: December 2004

Stabilization energies and equilibrium distances of one‐dimensional (HF)n and (H2O)n chains have been calculated by means of the PCILO method for finite chain length and by the PCILOCC method for infinite chain length. Both types of calculation are compared with corresponding CNDO/2‐MO and CNDO/2‐CO calculations. Further we have performed an analysis of the individual contributions of the stabilization energies per monomer of the PCILO and PCILOCC calculations.

The results show that the PCILOCC method is well suited for the calculation of molecular associations with translational symmetry.
Molecular calculations with the MODPOT, VRDDO, and MODPOT/VRDDO procedures. IV. Boron hydrides and carboranes
Authors: Popkie Herbert E. , Kaufman Joyce J.
Published: December 2004

Reference completely ab initio 6–3G and nonempirical 3G/MODPOT (ab initio effective core model potential) LCAO‐MO‐SCF calculations (using the same valence atomic orbital basis) were performed for a series of boron hydrides (B4H10, B5H9, B5H11, and B6H10) and a test 3G/MODPOT + VRDDO (variable retention of diatomic differential overlap for charge conserving integral prescreening) calculation were also performed for B5H9, B6H10, and B10H14. The agreement between the ab initio 6–3G and the corresponding 3G/MODPOT calculations was excellent for valence orbital energies, gross atomic populations, and dipole moments. The results also compared favorably to previous ab initio minimum STO basis results of Lipscomb and coworkers. The 3G/MODPOT + VRDDO calculations verified that for such spatially compact molecules (such as boron hydrides, which are fragments of polyhedra), the VRDDO procedure does not result in a noticeable savings in computer time for molecules of the size and shape of B5H9 and B6H10, in contrast to the savings previously realized for organic molecules of comparable atomic size. However, the agreement in calculational results between the 3G/MODPOT and the 3G/MODPOT+VRDDO results was still as extremely close as it had been for the organic molecules.

3G/MODPOT calculations were also carried out for B8H12, B9H15, B10H14, B10H14−2, 1,2‐C2B4H6, and 1,6‐C2B4H6 and the results compared to the previous minimum STO basis results. For B10H14, the 3G/MODPOT+VRDDO method led to savings in computer time of 28% over the 3G/MODPOT method itself.

The agreement of the 3G/MODPOT results with available experimental photoelectron spectral data for B5H9 and 1,6‐C2B4H6 was as good as that of the previous ab initio minimum STO basis calculations.
Electronic structure of TCNQ, studied with HAM/3
Authors: Åsbrink L. , Fridh C. , Lindholm E.
Published: December 2004

The electronic structure of tetracyanoquinodimethane (TCNQ) is calculated using the new semiempirical method HAM/3. The calculated photoelectron spectrum is in reasonable agreement with the measured spectrum. The excitation energies are obtained directly in HAM as the differences of the energies of the unoccupied and the occupied orbitals. The calculated UV spectrum is in good agreement with the measurements. The weak band at 5.3 eV, which earlier had been assumed to correspond to a forbidden transition, is allowed according to HAM. The electron affinity is also in reasonable agreement with the measured value. An explanation has been given for the experimental observation of several resonance states (negative electron affinities). p‐Quinodimethane has also been studied.
A comparative study of multiple scattering calculations on CrF63−
Authors: Kai Aldwyn Tang , Larsson Sven
Published: December 2004

The multiple scattering molecular orbital method, with different choices of sphere radii and local exchange, is applied to the cluster CrF63−. The orbital energies are almost always in the same order but uniformly moved up or down the energy scale depending on which parameters are used. Charge densities are only slightly dependent on the parameters. A method to avoid interaction with Rydberg‐like states is suggested.
Complex coordinate calculations of resonances in N‐electron atoms
Authors: Junker B. R.
Published: December 2004

We present a discussion of the functional dependences of the wave functions for bound, resonant, and scattering states on the radial coordinate ρ and the rotation angle α in the complex coordinate method. We conclude that for bound states and resonances, ρ and α are constrained to appear in the wave functions only in the for ρ exp(iα). On the other hand, this constraint is not obtained for the scattering states since the energy of the scattering states depends on α. In addition we suggest a partitioning of the resonant wave function into two parts—a boundlike or “Q‐space” part and a scattering like or “P‐space” part. With these concepts one can incorporate physical insight into the choice of configurations as one does in other methods and can apply the complex coordinate method to many electron systems with an expected rate of convergence similar to other techniques. Its advantages are that a single calculation yields the position and width of the resonance, only square integrable functions are used, only a solution of a straightforward eigenvalue problem is required unlike some methods, arbitrarily accurate target states are easily incorporated, and polarization terms can easily be explicitly included. Variational calculations for the position and width of the lowest 2S resonance in the negative helium ion are reported using trial wave functions containing 39, 43, 55, 24, and 32 “P‐space” configurations, respectively. Values of 19.387 eV and 12.13 meV are obtained for the position and width, respectively, for the resonance over a range in the rotation angle of almost two orders of magnitude. One also finds that inclusion of free‐particle‐like basis functions improves the representation of the scattering states.
Resonances and complex scaling: A rigorous overview
Authors: Simon Barry
Published: December 2004

We review certain aspects of the theory of resonances and give a comprehensive review of the rigorous aspects of complex scaling.
Closed‐shell SCF–CIMO treatment of all‐reactive electrons in complex heteroorganic molecules
Authors: Hilal Rifaat
Published: December 2004

A semiempirical molecular orbital (MO) method is outlined that is designed for correlation and prediction of the spectra and other properties of complex molecules. Within the ZDO approximation, the reactive (π‐bonding and nonbonding) electrons are treated explicitly considering the σ electrons as an unreactive static potential. The electronic repulsion integrals are evaluated using the multipole expansion formulas, which allow the characterization of each orbital by specification of its quadrupole moment, from which all two‐center repulsion integrals involving it would be computed. A preliminary application of the all reactive electron self‐consistent field (ARE‐SCF‐CI) MO method is made to organic carbonyls as well as some selected cyanine dyes. The predicted n → π* and π → π* transition energies and intensities are in good agreement with experimental data. The calculated ionization potentials are 0.2–0.7 eV lower than the observed values. The present method, although it requires further possible refinements, bridges the gap between the simplicity of the PPP method and the required overall interpretation of the electronic properties.
Diatomics‐in‐molecules study of LiOH
Authors: Nemukhin A. V. , Stepanov N. F.
Published: December 2004

The diatomics‐in‐molecules method is applied to calculate the ground state 1A′ potential energy surface for LiOH. Three different sets of polyatomic basis functions are investigated. An adequate description of the surface is obtained only with the set including both neutral and ionic atomic states.
Atomic energy levels and oscillator strengths calculated with a screened potential
Authors: Wu Irene C. , Miller Kenneth J.
Published: December 2004

A screened potential model (SPM) is formulated with Slater‐type functions to reproduce the density of the electron shells. The orbital exponent for the valence shell is optimized to calibrate the SPM against experimental valence and Rydberg s and p energy levels for the alkali metals (Li, Na, and K) rare gases (He, Ne, Ar, and Kr), second‐row atoms, and Cu, Zn, Mg, S, and Ga. The resulting one‐electron wave functions are used to calculate the dipole and velocity forms of the oscillator strengths and 〈1/r3〉 for spin‐orbit coupling. The excellent agreement with the averaged experimental results suggests that the SPM atomic orbitals are a good starting point for the evaluation of one‐electron properties.
Fourth‐Order terms in the diagrammatic perturbation expansion for the electronic energy of atoms and molecules
Authors: Wilson Stephen , Silver David M.
Published: December 2004

Third‐order diagrammatic perturbation theory provides a simple and accurate description of the electronic structure of atoms and molecules beyond that afforded by independent electron models. The largest corrections to such treatments, the fourth‐order terms, are presented and discussed. All of the diagrams, which arise when the closed‐shell Hartree–Fock function is utilized as a reference function, are given through fourth order.
Perturbative configuration interaction using localized orbitals in the INDO hypothesis. I. Theory and applications to energetical problems
Authors: Douady J. , Barone V. , Ellinger Y. , Subra R.
Published: December 2004

A complete development of the PCILO method is presented for the INDO approximation. The introduction of exchange terms in the theoretical treatment is discussed and a detailed analysis of the successive contributions to the total energy is given. The method is applied to various conformational problems (geometry optimization, rotation, and inversion barriers). Its ability to deal with biological systems is tested on the acetylcholine neurotransmitter. Inversion barriers are highly improved with respect to the corresponding CNDO algorithm. A better account of σ‐π exchange phenomena can be expected with the presented PCILO‐INDO development.
Quantum‐chemical investigation of the silicon and carbon coordination bond in their isostructural compounds
Authors: Vitkovskaya N. M. , Mantsivoda V. B. , Moskovskaya T. E. , Voronkov M. G.
Published: December 2004

Ab initio calculations within the minimal basis set of STO‐4LGTO have been carried out on molecules of type H3MX (M = Si, C; X = H, NH2, OH, F). The influence of the MH3‐group inversion on the electronic structure of these compounds has been investigated and illustrated by MO electron density maps. The ability of the central atom to form an additional bond has been estimated with the help of calculations on the complexes of these molecules with the hydrogen negative ion. The complexes of type [H4SiX]− have been found to be more stable than their unbonded components. The [H4CX]− complex formation has not proved to be advantageous.
Further analysis of the iterative hypervirial‐scaling method
Authors: Fernández Francisco M. , Castro Eduardo A.
Published: December 2004

A previously given iterative procedure to improve wave functions is analyzed. Its relationship with other well‐known approximation methods is investigated. Hypervirial operators depending on a real parameter are proposed and their connection with the employment of an infinite number of hypervirial relations is analyzed. A way to use formulas that are valid for exact eigenfunctions in the case of approximate functions is presented. Formal results are applied to the harmonic oscillator and hydrogen atom models in order to show their practical utilization.
Ab initiomolecular orbital study of the hydrogen‐bonded pyrrole ⃛acetonitrile complex
Authors: Lumbroso Henri , Pappalardo Giuseppe Concetto
Published: December 2004

The total dipole moments, molecular energies, and π‐electron densities for the linear and orthogonal pyrrole ⃛acetonitrile hydrogen‐bonded complexes were studied in theab initiovalence bond framework using the minimalSTO‐3G basis set. That the orthogonal conformation, although slightly less stable than the other, is predominant as observed in carbon tetrachloride, can be explained by its relatively high symmetry number.
Potential‐energy surfaces in the lower excited states of benzene⇌Dewar–benzene isomerization process
Authors: Tsuda Minoru , Oikawa Setsuko , Kimura Katsuhiko
Published: December 2004

Adiabatic potential‐energy surfaces in the lower excited states following the benzene⇌Dewar–benzene isomerization process were calculated by the INDO/S method postulating the concerted reaction mechanism which is proved to be valid in the ground state by the calculation of the intrinsic reaction coordinate. It was concluded that the benzene molecule in the 1B1u and 1E2u excited states readily isomerizes to Dewar–benzene in the condensed phase although the quantum yield may not be large. Bryce‐Smith's proposal, that the isomerization to Dewar–benzene occurs only after the intersystem crossing to the 3B1u state in benzene molecule, will not be probable; for the 3B1u route is not favorable to the isomerization in comparison with these singlet routes. However, the rearomatization of Dewar–benzene in the ground state may produce the 3B1u benzene in small yield with higher yield of the ground‐state benzene. The activation energy in the rearomatization is calculated to be 19.03 kcal/mol. These conclusions are consistent with the experimental facts. Molecular orbital correlations in the isomerization and the ionization potentials of Dewar–benzene were also discussed.
Parametrization of the equations‐of‐motion method for conjugated hydrocarbons
Authors: Shibuya Tai‐Ichi , Funada Tadashi
Published: December 2004

The equations‐of‐motion (EOM) method has been parametrized for the evaluation of the “π → π*” transition energies and moments of conjugated hydrocarbons. In this new semiempirical scheme, the effect of the dynamical screening by σ electrons is explicitly included.
Binding energies at different momenta for the valence orbitals of HCl by the binary (e, 2e) method
Authors: Suzuki I. H. , Brion C. E. , Weigold E. , Williams G. R. J.
Published: December 2004

The binding energy spectra for the valence orbitals of hydrogen chloride have been obtained using the binary (e,2e) method at 1200 eV. The strength of the innermost valence orbital (4σ) is severely split among several ion states in the energy range 25 to 41 eV. The measured cross sections are compared with results of calculations using contracted Gaussian basis sets of double‐zeta quality, and with a one‐particle Green's function calculation.
Comparison between intervalence charge transfer and molecular tautomerism
Authors: Chu San‐Yan , Lee Shyi‐Long
Published: December 2004

The charge exchange process in the intervalence (mixed‐valence) system is interpreted in terms of the nonstationary state mechanism which is a well‐known approach for rationalizing the molecular tautomerism process. The two kinds of processes are viewed in a close analogy in the sense that both involve a pair of near‐degenerate levels in a double‐well potential. However, a comparison is made between the two cases to demonstrate that an electron moves not only faster but also farther in distance than a nucleus does.
Electronic structure of transition‐metal complexes. I. Parametrization for CNDO/2 method
Authors: Kai Eiko , Nishimoto Kichisuke
Published: December 2004

A new parameterization for the first transition metal has been proposed in the framework of CNDO/2 method. We carried out CNDO/2 calculation of hexamine complexes [M(NH3)6]2+ and hexa‐aquo complexes [M(OH2)6]2+ in the high spin state where M = Mn, Fe, Co, Ni, and Cu, using new parameters. It is shown that the calculated order of binding energy is MnL < FeL < CoL < NiL ≈ CuL (where L means the ligand), and is in good agreement with experiment. We discussed how the orbital nodes affect the nature of bonding between metal and ligand.
EHF Description of superexchange: Relations to Anderson's model
Authors: Mayer I. , Angelov S. A.
Published: December 2004

It is shown that the treatment of the superexchange in insulators, based on the spin projected extended Hartree–Fock (EHF) method may be considered as a direct generalization of Anderson's ligand field (or kinetic exchange) theory: the EHF methods permits to construct explicitly the effective orbitals for the magnetic electrons and to determine all the parameters occurring in Anderson's theory from only one variational problem.
Electronic spectra of nucleic acid bases: Variable electronegativity calculations and an analysis of existing results
Authors: Srivastava S. K. , Mishra P. C.
Published: December 2004

Variable electronegativity Pariser–Parr–Pople (VE‐PPP) calculations have been carried out on the bases of nucleic acids and 5‐fluorouracil. Directions of polarization for the various electronic transitions in these molecules have been calculated using the wave functions obtained by this and the CNDO/S‐CI methods. The calculated excitation energies, oscillator strengths, and directions of polarization have been compared with the PPP results due to Pullman and co‐workers and Bailey as well as the experimental ones. It has been found that a comparative study of this type is much more useful for understanding the transitions in the molecules than the individual calculations. The VE‐PPP method is found to generally give the best results. The directions of polarization have been used to identify the transitions in the molecules and to compare the excitation energies obtained by different methods. It is shown that the transitions in these molecules do not have the characteristics of those of benzene derivatives. All the observed peaks in the molecules have been explained as π*→π.
Configuration interaction matrix elements. III. Spin functions relating the unitary and symmetric group approaches
Authors: Wormer P. E. S. , Paldus J.
Published: December 2004

Spin functions that are compatible with orbital ordering and geminal antisymmetry conditions are investigated. It is shown that two widely used classes of spin functions, namely, the spin‐bonded functions and Yamanouchi–Kotani (or, equivalently, Gelfand–Tsetlin) functions possess these properties. The relationship of the latter with Young–Yamanouchi spin functions is also outlined using graphical techniques of spin algebras. These techniques are also used to rederive the Hamiltonian matrix elements between spin‐bonded functions and to show the relationship among the various schemes used in this case.
Nonconservation of excitons as a mechanism of light‐energy capturing
Authors: Hadžiselimović E. A. , Marinković M. M. , Tošić B. S.
Published: December 2004

The analysis of nonstationary processes, taking place in exciton systems in consequence of the nonconservation of the number of elementary excitations, is presented and it is pointed out to a new possibility of light‐energy capturing which exists in ecological systems due to the nonconservation of excitons. It is shown that, due to the nonconservation, the one‐dimensional molecular chain is able to capture permanently the light energy of the order of 50 keV to 5 MeV. A part of the captured energy is expected to have a role in internal bioprocesses. It is also shown that the system is a seat where the processes of continuous creations and annihilations of pairs of excitons having opposite momenta take place with a probability of the order of 10−4 to 10−2. Further investigations would allow to identify biological phenomena caused by those processes.
Thermal dissociation of 1,2‐dioxethane. III. Localized molecular‐orbital study
Authors: Hilal Rifaat
Published: December 2004

The localized MO's (LMO's) of 1,2‐dioxethane in its ground state and along the dissociation reaction path (to formaldehyde products) are generated using Boys' criteria for localization. The total charge density in each LMO is partitioned into atomic and overlap densities and the binding or antibinding character of each LMO is discussed in terms of the forces exerted on the nuclei by these densities. The driving force for the dissociation reaction is shown to arise essentially from the atomic dipole forces exerted on the oxygen nuclei by their lone‐pair LMO's. The characterization of a saddle point on the potential energy surface has been discussed in terms of the electrostatic equilibrium between forces exerted by the electron clouds “incomplete following” and “preceding.” The differences between the LMO's obtained from the two Hartree–Fock solutions to which the SCF procedure converges have been discussed.
Theory of the potential of a donor ion in silicon
Authors: Csavinszky P. , Morrow R. A.
Published: December 2004

In this paper a variational principle has been formulated for obtaining an approximate solution of Poisson's equation for the potential of a donor ion embedded in Si. A comparison of a two parameter approximate analytical potential with the exact numerical potential shows excellent agreement for several electron concentrations. It is also found that the present theory, using the concept of a “spatially variable dielectric constant,” leads to a donor‐ion potential which deviates significantly from the potential of Dingle, which has been the traditional starting point of calculations of electron mobility limited by ionized‐impurity scattering.
Dynamics and conformation of polypeptides
Authors: Gupta V. D.
Published: December 2004

The dynamics of simple polypeptides is studied both from theoretical and experimental viewpoints. Theoretically, dispersion curves and frequency distributions are obtained from Wilson's GF matrix method as modified by Higgs for an infinite helical system. The systems studied are polyglycine I and polyglycine II, polyalanine in α and α forms, poly‐L‐proline I and poly‐L‐proline II, and poly‐L‐hydroxyproline. Conformation sensitive modes and their dispersion in the BZ are reported. In several of these, the results are compared with the measurements from inelastic neutron scattering. Since the neutrons have a large incoherent scattering cross section for hydrogen, it enables us to examine a normal mode via the motion of protons involved. In addition, neutron scattering is not controlled by symmetry dependent “selection rules.” Conformational studies of oligomers of glycine, alanine, and proline in relation to their polymeric forms as deduced from the dispersion curves and spectroscopic studies are presented. Recent measurements on the specific heat of polyglycine and polyalanine by Finegold et al. are also reported.
Protein backbone interaction with nucleic acid base pairs: A theoretical investigation
Authors: Hosur Ramakrishna V. , Pohorille A.
Published: December 2004

A novel model of interaction between peptide backbone and nucleic acid base pairs, proposed earlier on the basis of model building studies has been theoretically investigated. Interaction energies for two different schemes of H‐bond interaction between peptide backbone and base pairs AU and GC have been calculated for different conformations of peptide backbone. The different H‐bond parameters have been calculated. The importance of such an interaction in specific recognition has been discussed in light of the results of theoretical calculations.
Theoretical model for exploration of catalytic activity of enzymes and design of new catalysts: CO2 hydration reaction
Authors: Sokalski W. Andrzej
Published: December 2004

The quantum chemical model for predicting the optimal molecular environment exerting the highest catalytic activity on transition complex has been proposed. It was applied for the CO2 hydration reaction at the nonempirical LCAO MO SCF level. The possible use of the resulting optimal charge distribution of environment for design of new synthetic catalysts and explanation of the carbonic anhydrase action was discussed. In addition, a simplified approach based on the difference electrostatic molecular potentials evaluated within the many center multipole expansion is presented. It may enable us to perform corresponding estimations even by means of a programmable calculator.
Interaction between polymers: Dispersion energy of two infinite linear chains
Authors: Beleznay F. , Suhai S. , Ladik J.
Published: December 2004

Using the newly developed discrete variant of the k · p perturbation theory for linear chains an expression is derived for the dispersion interaction between two infinite chains valid for both insulating and metallic polymers. It is shown that the formally divergent dispersion energy is also finite for metallic systems, but it may be considerably enhanced in polymers with partly filled bands as compared with insulting ones. The accuracy of the proposed k · p expansion is investigated on model chains through comparisons with direct ab initio Hartree–Fock crystal orbital calculations. Applying second order perturbation theory an explicit formula in terms of band parameters is given for the numerical calculation of the dispersion energy.
Relativistic theory of binding energies of heavy positive ions
Authors: Marini U. , Marconi Bettolo , March N. H.
Published: December 2004

The self‐consistent relativistic Thomas–Fermi theory of heavy positive ions with N electrons and nuclear charge Ze is shown to lead to a chemical potential μ which has the scaling property

with ϵ = α2Z2, α being the fine structure constant. Combining this with the Layzer–Bahcall expansion for the total energy E(Z, N), namely,

it is proved that the coefficients Enm (N) at large N have the asymptotic behavior Nn–2m/3#1/3. The corresponding result for the scaling of the relativistic Thomas–Fermi energy is

Scaling properties of the higher order terms in Enm (N) and E(Z, N) are also proposed.
Hyperviral extension for energies of parameter‐dependent systems
Authors: Ferńndez Francisco M. , Castro Eduardo A.
Published: December 2004

The energy of a linearly perturbed enclosed system is calculated by way of the hypervirial methodology in the semiclassical limit. Solutions of this equation are compared with the exact as well as with WKB approximate results for the harmonic oscillator model.
Electron correlation described by extended geminal models: The EXGEM2 and EXGEM3 models
Authors: Røeggen I.
Published: December 2004

The general extended geminal model is reviewed and two new approximate models EXGEM2 and EXGEM3 are introduced. In a test calculation on water using a double‐zeta basis set, the approximate models recover 93.4% of the full CI correlation energy defined within the same basis set. A test calculation on the neon atom demonstrates that the performance of the models in comparison with the full CI, will improve as the basis set is increased. It is suggested that for basis sets of moderate and large size, and which include polarization functions, the extended geminal models are likely to recover 95%–97% of the correlation energy obtainable by the full CI.
Quantum chemical calculation of phosphorescence microwave double resonance spectra
Authors: Minaev B. F. , Muldahmetov Z. M. , Irgibaeva I. S. , Tlepbergenov T. O. , Kizhner D. M.
Published: December 2004

Lifetimes of individual spin sublevels, vibronic intensities of phosphorescence, zero field splitting, hyperfine and nuclear quadruple tensors for the lowest triplet state, g factors, and dipole nature of microwave transitions have been calculated on the bases of CNDO and INDO methods taking into account spin–orbit, spin–spin, vibronic, and hyperfine interactions by perturbation theory. The results are in qualitative agreement with phosphorescence microwave double resonance data. Influence of intermolecular interaction on the zero field splitting are also investigated.
Coherent multiphoton absorption: Dependency on the relative phase of two successive pulses
Authors: Besnainou Sylvette , Stone James , Diels Jean‐Claude
Published: December 2004

When a multilevel system excited by a laser pulse absorbs a cascade of photons, a second pulse of same frequency, equal duration but dephased by π takes it back to its initial state. This property can be inferred by studying the laser field system interaction matrix, using the rotating wave approximation.
Towards a “Chemical” Hamiltonian
Authors: Mayer I.
Published: December 2004

An analysis of the LCAO Hamiltonian is performed in terms of a “mixed” formulation of the second quantization for nonorthogonal orbitals, compressing the different interactions to one‐ and two‐center terms as far as possible by performing appropriate projections. For this purpose an operator of atomic charge is also introduced, the expectation values of which are the Mulliken gross atomic populations on the individual atoms. The LCAO Hamiltonian is decomposed into terms having different physical meaning and significance: (i) sum of effective atomic Hamiltonians; (ii) the electrostatic interactions in the point‐charge approximation; (iii) the electrostatic effects connected with the deviation of the actual charge distribution from the pointlike one; (iv) two‐center overlap effects; (v) finite basis (“counterpoise”) correction terms related to the individual atoms; and (vi) similar finite basis correction terms with respect to the two‐center interactions. Only terms of types (i) to (iv), containing no three‐ or four‐center integrals, are considered as having physical significance. Based on the analysis of the Hamiltonian, an energy partitioning scheme is developed, and explicit expressions are given for one‐ and two‐center (and basis extension) components of the SCF energy. The approach is also applied to the problem of intermolecular interactions, and an explicit formula is given permitting calculation of the “counterpoise” part of the supermolecule energy by properly taking into account that it depends not only on the extension of the basis, but also on the occupation of the additional orbitals in the intervening molecule—a factor completely overlooked in the usual scheme of calculations.
Some remarks on the hydrogen atom
Authors: Grinberg Horacio , Marañon Julio , Vucetich Hector
Published: December 2004

The path integral for the Green's function involving the Coulomb potential in combination with the Kustaanheimo‐Stiefel transformation is used to generate the atomic orbitals of the nonrelativistic hydrogen atom as various combinations of the product of one‐dimensional isotropic harmonic oscillator wave functions. The use of the transformation is justified, by connecting the homogeneous space with the quotient space in the Feynman quantization formalism.
Incidence of the relativistic corrections in electronic properties of 5d compounds: MS–Xα Calculations on hexachloroiridates (III and IV) and tungsten trioxide
Authors: Chermette H. , Pertosa P. , Goursot A. , Penigault E.
Published: December 2004

Multiple‐scattering–Xα (MS–Xα) calculations have been performed on IrCl, IrCl, and WO clusters. Relativistic calculations have been performed by the inclusion of the approximation of Wood and Boring in the MS–Xα method, i.e., mass–velocity and Darwin terms are taken into account self‐consistently, while the effects of the spin–orbit operator are estimated by first‐order perturbation theory. The strong contraction of s and p orbitals can be seen on selected displays of radial wave functions and significant changes in the energy diagrams between the nonrelativistic and the relativistic calculations can be obtained. The comparison with photoemission spectra clearly shows the necessity of including relativistic corrections in the calculations. The calculated spin–orbit parameters are in agreement with experiment for core levels, while a strong dependence of the spin–orbit parameters on the one electron energies is pointed out; this dependance is unconnected from the atomic contributions to the molecular orbitals.
Routes to full CI through extrapolation in multireference configuration calculations for electronic structures
Authors: Burton Peter G.
Published: December 2004

“Full CI” energy extrapolation techniques for use with MRDCI (or MCSCF‐CI) wave function calculations are illustrated for (H2)2 which is “pathological” [C. F. Jackels and I. Shavitt, Theor. Chim Acta 58, 81 (1981)]. Our analysis suggests that this extrapolation should be fundamentally more reliable than cluster correction formula results, through the application of a double internal consistency scaling of systematic error estimates, despite explicit treatment of only a small fraction of the configuration list of a full CI. The results of extrapolation suggest that the van der Waals interaction for H2–H2 at R = 6.5a0 in the planar T configuration is less than 200 μH greater than our semiempirical estimate for this interaction strength. Although the role played by the limited basis (80 functions) is not assessed by the present calculations, it appears possible that absolute errors from extrapolation from 16255 SAF results to estimate the full CI value (912464 SAF's) are as small as 0.5 kJ/mol.
Theoretical studies on the conformation of saccharides. V. Hydration of the acetal segment in glycosides
Authors: Tvaroška Igor , Kožár Tibor
Published: December 2004

Hydration sites of the acetal segment were studied in five of the most stable conformers of 2‐methoxy‐tetrahydropyran (MTHP) as the first step in the determination of the hydration scheme of glycosides. The intramolecular geometries of a supermolecule formed with MTHP and water were calculated by a PCILO quantum‐chemical method. The hydration sites determined can be classified into two groups: (a) individual sites, in which water interacts with one oxygen only, and (b) bridging sites, in which water interacts with both oxygens. The interaction energies of the individual sites are approximately 22 kJ mol−1, and 26 and 29 kJ mol−1 in the bridging sites. An increase of the number of water molecules in the hydration shell of MTHP showed that monohydration of the glycosidic linkage oxygens was most advantageous. Despite of the fact that the hydration shell have various structures in the individual MTHP conformers, the obtained results indicate that the hydration does not operate against the anomeric or exoanomeric effects, i.e., it does not influence the equilibrium of the MTHP conformers in favor of the trans arrangements of a glycosidic bond. Therefore, the experimentally observed stabilization of the trans positions in aqueous solutions should be considered as a result of influence of water being a dielectric continuum.
Conformational and MO studies of hydroxy‐2‐aminotetralins
Authors: Kocjan D. , Šolmajer T. , Hodošček M. , Hadži D.
Published: December 2004

Attempting to explain the differences in the pharmacological profiles of the isomeric monohydroxy‐and dihydroxy‐2‐aminotetralins (DHAT) which are potent dopaminergic agonists we have calculated the conformational energies of 2‐aminotetralin and its N,N‐dipropyl derivative using the QCFF/Pi and PCILO methods. Molecular electrostatic potential (MEP) maps based on ab initio (STO‐3G) wave functions were computed for both dihydroxytetralins. Root‐mean‐square (rms) deviations from steric congruence between the enantiomeric 5,6‐ and 6,7‐DHAT based either on atomic centers or on the minima in MEP near the putative points of attachment to the receptor are small, but may nevertheless be sufficient to cause differences in activity on subtypes of the dopamine receptor. N,N‐dipropyl substitution influences the conformational energies of the skeleton and the preferences in the orientation of the propyl groups in the isomeric DHAT may be important for the interaction with the receptor. The HOMO energies of the isomeric HAT and DHAT do not correlate with their potencies.
Spectroscopy with sound on superfluid 3He B
Authors: Lee D. M.
Published: December 2004

Collective modes of superfluid 3He B have been studied by means of sound attenuation and sound velocity studies. A new sound attenuation peak has been observed in superfluid 3He B at ħω ≈ Δ(T). This peak has been identified with the real squashing mode. Pulse time of flight methods has been used in these studies. At high sound amplitudes, interesting transient effects have been observed which have been tentatively identified with solitonlike behavior.
Generator coordinate treatment of some model periodic systems
Authors: Kauder L. R. , Ray A. K. , Trickey S. B.
Published: December 2004

The generator coordinate method (GCM) is a powerful variational technique invented for studying nuclear collective motion and extended in recent times by Lathouwers, Van Leuven, and Laskowski et al. to problems of molecular electronic structure and vibrations. In preparation for the application of GCM to electron correlation and lattice dynamical problems in solids, we have studied linear periodically bounded systems consisting of one‐ and two‐mass anharmonic chains of both finite and infinite length. Preliminary results for the variational energy and vibrational spectra from some simple intrinsic functions are presented.