bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport of excitation energy in a doped molecular aggregate. III. numerical investigation of exciton hopping with various exciton‐depleting processes
Authors: Datta Sambhu N. , Prabhu N. V. 
Published: January 2005

AbstractA brute‐force numerical investigation has been carried out on the hopping of excitons in a three‐dimensional molecular aggregate. Possibilities of vibronic decay, rapid chemical reactions of saturated species, radiative decay of overpopulated molecules, and cooperative chemical reactions involving saturated exciton populations on traps of two different types have been considered. Investigation have been performed with two types of initial distribution of excitons—facial and random—and for 10,000 or, sometimes, for 20,000 time steps each of duration 1ps. Several interesting observations have been made from this computer experiment: (1) The total number of occurrences of fast reactions depends upon the initial distribution of excitons. (2) It decreases if other exciton depleting processes are at work. (3) It also depends on the pattern of placement of traps. (4) The location of impurities also affects the rate of occurrence of these reactions. Thus, more reactions occur when the excitons are initially concentrated on one face and traps are suitably located on the path of flow of these excitons. A random initial distribution tends to equilibrate the excitons quickly over all the lattice points, thus giving rise to fewer reactions. (5) The number of reactions need not necessarily increase with the number of reaction centers; in fact, it decreases as more centers are added when the supply of excitons is severely limited. (6) A Complicated dynamics results when different types of additional processes, viz., enhanced fluorescence, radiative emissions, and cooperative chemical reactions are simultaneously allowed. The cooperative process has been clearly found to dominate. A first‐order rate constant of about 108 s‐1 has been calculated for the occurrence of the cooperative process. This rate is affected when other nonconserving processes are switched on. Observations (1), (4), and (5) are the most important conclusions of our work. They lie outside the scope of traditional models such as the random walk model, the diffusion model, and the lattice model for the migration of excitons in a molecular aggregate. © 1993 John Wiley & Sons, Inc.
Complex scaling and Lyapunov converters
Authors: Kumičák Juraj , Brändas Erkki J. 
Published: January 2005

AbstractIt is proved that for a certain class of potentials dilation operators used in the method of complex scaling (CSM) represent a special case of Lyapunov converters. The time evolution of quantum systems is investigated from the viewpoint of this result, with special emphasis on the time evolution of resonant functions. © 1993 John Wiley & Sons, Inc.
On the positivity condition in the nonunitary transformation theory of irreversibility
Authors: Brändas E. J. , Antoniou I. E. 
Published: January 2005

AbstractThe Misra–Prigogine–Courbage Nonunitary Transformation Theory of Irreversibility is revisited in connection with the role played by the fundamental positivity preserving condition of the associated semigroup evolution. Comparisons between various viewpoints referring to general context of non‐Markovian formulations are given. Some recent criticism of the Misra–Prigogine–Courbage theory regarding attempts to derive irreversibility and the approach to equilibrium without any approximations and/or loss of information is corrected. © 1993 John Wiley & Sons, Inc.
Generalized spectral decompositions of mixing dynamical systems
Authors: Antoniou I. , Tasaki S. 
Published: January 2005

AbstractWe introduce a method for the explicit computation of the eigenvalue problem of the evolution operator of mixing dynamical systems. The method is based on the subdynamics decomposition of the Brussels–Austin groups directed by Professor I. Prigogine. We apply the method to three different representatives of mixing systems, namely, the Renyi maps, baker's transformations, and the Friedrichs model. The obtained spectral decompositions acquire meaning in suitable rigged Hilbert spaces that we construct explicitly for the three models. The resulting spectral decompositions show explicitly the intrinsic irreversibility of baker's transformations and Friedrichs model and the intrinsically probabilistic characters of the Renyi maps and baker's transformations. The dynamical properties are reflected in the spectrum because the eigenvalues are the powers of the Lyapunov times for the Renyi and baker systems and include the lifetimes for the Friedrichs model. © 1993 John Wiley & Sons, Inc.
Amplitude squared squeezed states in the Fock–Bargmann space
Authors: Martín M. , Sandoval L. , Rivas‐silva J. F. , Palma A. 
Published: January 2005

AbstractSqueezed states are normally studied in configuration space or using the Glauber formalism for the coherent states. Here we show that the use of the Fock–Bargmann space can lead to more general solutions, especially in the case of squeezed states associated with the square of field amplitude. The relations that we obtain are completely general and several well‐known, approximate results can be obtained as the limit cases of our approach.© 1993 John Wiley & Sons, Inc.
The hydrogen atom in a semi‐infinite space limited by a hyperboloidal boundary
Authors: Ley‐Koo E. , Mateos‐Cortés S. 
Published: January 2005

AbstractThe hydrogen atom in a semi‐infinite space limited by a hyperboloidal boundary, with the nucleus at a focus, is investigated as a model of an atom on the surface of a solid. The energy eigenvalues, hyperfine structure, and electric dipole moment of the system are evaluated for different focal distances and eccentricities of the boundary. It is shown that the system tends to become infinitely degenerate at the ionization threshold as the boundary closes in approaching the nucleus. This model includes as special cases the corresponding models in the literature with plane and paraboloidal boundaries. © 1993 John Wiley & Sons, Inc.
Related upper and lower bounds to atomic binding energies
Authors: Tai C. C. , Vatsya S. R. , Pritchard H. O. 
Published: January 2005

AbstractThe method proposed by Singh for the calculations of lower bounds to atomic binding energies has been generalized to encompass upper bounds as well. The result is a pair of related matrix eigenvalue problems, constructed from similar sets of basic matrix elements, with the solution of one yielding the tower bound, and of the other, the upper bound. The upper bounds are identical to those calculated by the Rayleigh–Ritz method, which can be useful when the inversion of the normalization matrix is ill‐conditioned. The lower bounds are comparable with the best available in the literature. © 1993 John Wiley & Sons, Inc.
Analytical calculation of the electrostatic interaction energy within the CNDO framework
Authors: Dehareng D. , Dive G. , Ghuysen J. M. 
Published: January 2005

AbstractThis work analyses the adequacy of an analytical electrostatic energy formulation within the CNDO framework to predict the stable conformations of large molecular complexes. Comparisons are made with abinitio results for small systems such as water‐formamide, methanol‐water‐imidazole, or guanine‐cytosine and with AM1 results for two large systems: a molecular tweezer + the 9‐methyladenine complex and a model active site of the α‐chymotrypsin and its ligand complex. This approach is efficient in providing reliable confromers for large molecular systems in a very fast way. © 1993 John Wiley & Sons, Inc.
Optimally convergent determinantal expansion of many‐electron wave functions
Authors: Thephilou A. K. , March N. H. 
Published: January 2005

AbstractIt is shown that the many‐electron wave function can be expanded optimally in terms of a set of slater determinants that reduces considerbly the number of determinats differing by a single‐particle wave function. The method is based on a variational procedure. The first step of the present method is the Brueckner optimization. The other determinants of the expansion are obtained by successive optimizations performed under additional constraints. The method is illustrated by specifically three‐and four particle example. Finally, it is concluded that the eigenstates of a many‐ particle system can be approximated by states that neglect single‐particle excitations. The Zero‐order approximation of the present scheme is the Hartree–Fock approximation. © 1993 John Wiley & Sons, Inc.
A numerical integration scheme for the evaluation of correlation energy functionals
Authors: Fortunelli Alessandro , Salvetti Oriano 
Published: January 2005

AbstractA numerical integration scheme is presented for three‐dimensional integrals occurring in electronic structure calculations, concentrating attention on the evaluation of the correlation energy through a density‐functional expression. The scheme is based on the choice of density‐based weight functions that naturally partition the space into “atomic” volumes (in which the integration is performed in terms of spherical coordinates) and “diatomic” volumes (in which the integration is performed in terms of confocal elliptical coordinates). Such a choice is justified on the basis of the analytical behavior of the integrand. The attainable accuracy and the required computational effort within the proposed scheme are discussed in detail in a test application on the C60 molecule in the symmetrical configuration. Finally, a comparison with previously proposed schemes is presented. © 1993 John Wiley & Sons, Inc.
Decay dynamics of a metastable state in a time‐varying electric field: A three‐level prototypical system
Authors: Adhikari S. , Bhattacharyya S. P. , Bhattacharyya D. M. 
Published: January 2005

AbstractIn a numerical experiment, the dynamics of natural decay of a metastable state is shown to be strongly affected by the presence of an external time‐varying electric field of high intensity. The metastable state, depending upon its level width, is shown to be stabilized by a near‐resonant electric field. The applied field may even cause population transfer to a neighboring bound level that is not directly populated by the natural decay process. The effects of continuous and pulsed perturbations are both analyzed numerically, and perturbation, theoretically. © 1993 John Wiley & Sons, Inc.
Computation of many‐center exchange integrals over Slater orbitals up to 4d by means of optimized Gaussian expansions
Authors: Montagnani Raffaele , Salvetti Oriano 
Published: January 2005

AbstractThe previously described optimization of small Gaussian expansions, to be employed for the computation of many‐center two‐electron integrals over Slater basis sets, has been extended, with some refinements, up 4d orbitals. © 1993 John Wiley & Sons, Inc.
Ab initio potential energy function for the dynamics of the fluoronium ion
Authors: Gianturco F. A. , Buonomo E. , Semprini E. , Stefani F. , Palma Amadeo 
Published: January 2005

AbstractThe various structures and geometries of the cation FH (fluoronium ion) have been investigated over a broad range of relative orientations between the proton and the HF molecule using ab initio, correlated wave functions and focusing on the lowest‐energy channel that can lead to the production of vibrationally excited HF in the collisions with near‐thermal H+ atoms. Various quality controls have been carried out on the accuracy of the target molecule description and a reliable, overall structure of the vibrational–rotational potential energy surface is obtained, for the first time extensively enough, to carry out scattering calculations in the direct excitation channels for the rotovibrational modes. © 1993 John Wiley & Sons, Inc.
Least‐motion stepwise [2 + 2] ketene cycloadition pathways predict the more hindered cis‐cycloadducts
Authors: Firestone Raymond A. 
Published: January 2005

AbstractKetene cycloadditions give predominantly the more hindered product. This has been adduced as evidence for concerted antarafacial cycloaddition in accord with the Woodward–Hoffmann rules. However, stepwise mechanisms, heretofore discounted, are now shown to account for the products in a simple least‐motion manner that requires only that rotation in the intermediates be not greatly faster than cyclization. This requirement is amply supported by the literature. © 1994 John Wiley & Sons, Inc.
Net signs of molecular graphs: Dependence of molecular structure
Authors: Gutman Ivan , Lee Shyi‐Long , Luo Yeung‐Long , Yeh Yeong‐Nan 
Published: January 2005

AbstractThe concept of internal connectivity associates to each eigenvector of the molecular graph a graph with signed edges. We show that the respective edge signs can be deduced without knowing the graph eigenvectors. The dependence of the edge signs on molecular structure is elucidated. The sign of an edge whose end vertices are νr and νs is found to be the result of separate interactions through all paths connecting the vertices νr and νs. The analysis of the edge signs is particularly simple in the case of acyclic systems. © 1994 John Wiley & Sons, Inc.
Electron‐pair distributions and chemical bonding
Authors: Wang Jiahu , Smith Vedene H. 
Published: January 2005

AbstractThe electron‐pair (intracule and extracule) densities of the first‐row hydrides may be understood on the basis of the different chemical‐bonding schemes in this series. Thus, the LiH pair densities show a strongly ionic nature and may be fairly well described by Li+H−. The CH‐pair densities, on the other hand, may be approximated by the promolecular superposition of a carbon and a hydrogen atom with an accumulation of pair density in the internuclear region signifying covalency. In the case of FH, its pair densities show a predominately ionic structure and are closer to those of F−than to those of the promolecular superposition of a fluorine and a hydrogen atom. The slight deformation of longitudinal pair densities observed in FH is largely due to the presence of the H+. © 1994 John Wiley & Sons, Inc.
Local hardness revisited: Definition and the spin‐polarized Kohn–Sham formulation of density functional theory
Authors: Garza Jorge , Robles Juvencio 
Published: January 2005

AbstractThe definition of local hardness is clarified within the Kohn–Sham formulation of the density functional theory. Exact equations for the local hardness of open‐ and closed‐shell electronic systems are derived. It is found that the Kohn–Sham independent particle kinetic energy does not contribute to local hardness. The apparent contradiction with previous work of Parr et al. is cleared up when the local hardness definition is revised. © 1994 John Wiley & Sons, Inc.
On the space of eigenvectors of molecular quantum mechanics
Authors: Wulfman Carl 
Published: January 2005

AbstractAs the representative point on an electronic energy surface moves along any closed level curve, the corresponding electronic eigenvectors behave as does the normal to a Moebius strip when its foot is moved around the strip. This introduces a topology into the space of eigenvectors that is not envisaged in the definition of Hilbert space, but is fundamental to molecular quantum mechanics. Salient properties of these “non‐Hilbertian” vector spaces are established. © 1994 John Wiley & Sons, Inc.
Generalized bond orders
Authors: Randić Milan , Guo Xiaofeng 
Published: January 2005

AbstractWe introduce generalized bond orders defined in terms of weighted Kekule valence structures. The weights were determined by the contributions of linearly independent and minimal conjugated circuits in individual Kekule valence structure. When special values for the contributions of conjugated circuits of different size are assumed, one obtains quantities that show considerable similarity to the Pauling and the Clar's bond orders. Pauling bond orders are obtained when one assumes that all conjugated circuits make equal contribution to bond orders. © 1994 John Wiley & Sons, Inc.
Approximately N‐representable density functional density matrices
Authors: Soirat A. , Flocco M. , Massa L. 
Published: January 2005

AbstractFor the first time, we obtain practical density matrices approximately N‐representable by correlated‐determinant wave functions, which are functionals of the electron density and entirely defined by information obtainable from the X‐ray coherent diffraction experiment. © 1994 John Wiley & Sons, Inc.
Protonation of fused aromatic systems: Ab initio study of some model Wheland intermediates
Authors: Eckert‐maksić M. , Maksić Z. B. , Klessinger M. 
Published: January 2005

AbstractStructure and properties of Wheland's intermediates are studied in some model systems. The effect of the annelated small ring is simulated by bending two vicinal CH bonds in benzene toward each other. The extent of bending describes the ring‐size effect of a small fused fragment molecule. The electrophilic substituent is represented by a proton. Calculations at the HF/6‐31G* and MP2/HF/6–31G* levels of sophistication confirm the Mills–Nixon (MN) hypothesis. It is conclusively shown that ß‐complexes are more stable than are α‐protonated species. The results are interpreted in terms of the ground‐state density distribution dictated by rehybridization and of the transition structure π‐electron redistribution triggered by protonation. Their effects are additive to a large extent as far as CC bond distances are concerned. Energetic properties are determined by the interplay of two characteristic π‐electron localization patterns, one caused by the initial angular strain and the accompanying rehybridization related to the ground state and the other one occurring during formation of the proton σ‐complex. This interplay destabilizes α‐intermediates relative to ß‐intermediates. © 1994 John Wiley & Sons, Inc.
A comparative basis‐set study of NeH+ using coupled‐cluster techniques
Authors: Pendergast Phil , Heck John M. , Hayes Edward F. 
Published: January 2005

AbstractUnrestricted Hartree‐Fock, coupled‐cluster calculations are reported for the ground state of NeH+ using atomic basis sets of increasing size and accuracy for both Ne and H. The goal is to determine the basis set and coupled‐cluster level of calculation needed to obtain a NeH+ potential energy curve of known accuracy. Here, it is shown that calculations using a quintuple zeta basis at the coupled‐cluster singles and doubles level with noniterative triples, CCSD(T), predict a Ne—H bond dissociation energy that is within about 0.01 eV of the exact Born–Oppenheimer molecular electronic structure result. Spectroscopic constants determined using the Simons–Parr–Finlan procedure are found to be in very good agreement with the experimental results. Calculations at the augmented quadruple zeta level for the two lowest triplet excited states of the NeH+ species are presented. Both of these states separate into ground‐state Ne+ and H(1s). The resulting potential curves predict stable minima at the SCF, CCSD, and CCSD(T) levels with dissociation energies of about 0.07 eV. Spectroscopic constants from the potential curves and dissociation constants are reported. © 1994 John Wiley & Sons, Inc.
Electronic structure calculations of 1,3‐dipolar cycloadditions using density functional and Hartree–Fock methods
Authors: Sosa Carlos , Andzelm Jan , Lee Chengteh , Blake James F. , Chenard B. L. , Butler Todd W. 
Published: January 2005

AbstractLocal spin density (LSD) methods were used to study the concerted 1,3‐dipolar cycloadditions for fulminic acid plus acetylene, fulminic acid plus ethylene, and nitrone plus ethylene. Cartesian Gaussian double‐zeta split‐valence basis sets augmented with one set of polarization functions (DZVP) were used for the LSD calculations. The LSD calculations were performed with the LSD exchange functional (Dirac) and with the Vosko, Wilk, and Nusair correlation energy functional (VWN). Nonlocal spin‐density corrections (NLSD) were estimated with the exchange functional of Becke and the correlation energy functional of Perdew (VWN + BP) and Becke, and the correlation energy functional of Lee, Yang, and Parr (B‐LYP). Vibrational frequencies were computed at the VWN and B‐LYP levels by numerical differentiation of the analytical first derivatives of the energy. Each of these reactions was examined using Hartree–Fock and Møller–Plesset perturbation theory for comparison. Geometry optimizations were carried out at the Hartree–Fock level with the 6‐311G(d,p) basis set, and correlation energies were computed up to the MP4SDTQ/6‐311G(d,p) level of theory. For the reactions of fulminic acid plus acetylene, fulminic acid plus ethylene, and nitrone plus ethylene, our best estimated density functional barrier heights are 7.8 ± 1.5, 8.9 ± 0.3, and 11.05 ± 1.9 kcal/mol, respectively. These results are in reasonable agreement with the correlated wave‐function calculations and experimental estimates. © 1994 John Wiley & Sons, Inc.
A dimensionally scaled generalization of constrained search energy density functionals
Authors: Valone Steven M. 
Published: January 2005

AbstractA dimensionally scaled generalization of constrained search density functional theory allows access to some simple model problems. These might be valuable for testing and perhaps improving conventional density functionals. One specific model problem is solved: When extrapolated to infinite numbers of spatial dimensions, the energy density functional for spherically symmetric, two‐electron systems can be calculated to arbitrary accuracy. © 1994 John Wiley & Sons, Inc.
Equilibrium geometry and electronic structure of benzylidene, arylethylidene, and heterocyclic arylidene malononitriles
Authors: Moustafa H. , El‐Taher S. , Hamed Maher M. , Hilal R. 
Published: January 2005

AbstractThe equilibrium geometry of some benzylidene, arylethylidene, and heterocyclic arylidene malononitriles has been calculated within the framework of the MNDO–MO formalism. Various structural factors are analyzed and discussed in terms of localized and delocalized MOS and π‐interaction between methylene malononitrile (MMN) and aryl moieties. The possibility of charge transfer (CT) from aryl to MMN moieties has been examined. The presence of a heterocyclic ring introduces a small perturbation into the MMN nuclear frame. p‐Substituents have a pronounced effect on the magnitude and direction of the dipole moment. The variation of ionization potentials and bond order with the Hammet σ p are examined and a straight‐line relationship is obtained. The correlation between physiological activity and quantum mechanical properties is analyzed in terms of heat of formation, ionization potential, dipole moment, and charge density on the aryl ring. © 1994 John Wiley & Sons, Inc.
Electronic structure of DNA dimer units, d(AG) · d, (CT), d(TG) · d(CA), · d(GT), and d(GA), in A and B conformations by DV–Xα cluster calculations
Authors: Shinoda Takako , Shima Nobuyuki , Tsukada Masaru 
Published: January 2005

AbstractThe electronic structure of d(AG) · d(CT), d(TG) · d(CA), d(AC) · d(GT), and d(TC) · d(GA), which are stacked base pairs in the DNA double helix, are elucidated for A and B conformations in detail by DV‐Xα cluster calculations. By using the S̃r values of the O2 (and O3) of each phosphate in the clusters together with those calculated in previous articles, it becomes possible to treat chemical reactivities of phosphates as recognition sites for all DNA fragments. Contour maps of the wave function of the HOMO and LUMO for bases differ subtly among the clusters and show the various fields around the P ion induced by the respective stacking constructed from four kinds of bases. © 1994 John Wiley & Sons, Inc.