bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transmission‐line matrix models for solving transient problems of diffusion with recombination
Authors: Gui Xiang , de Cogan Donard 
Published: October 2003

AbstractStarting from the general telegrapher's equation, we investigate two nodal network constructions for modelling diffusion with recombination by means of the transmission‐line matrix (TLM) method. The diffusion effect is modelled by the series and shunt capacitance in one approach, and by the series inductance and shunt resistance in the other. Both approaches use the series and shunt resistances to model the recombination effect. The constraint of using both TLM networks for solving transient problems of diffusion with recombination is found to be identical in terms of the physics behind the numerical routines. A practical way of determining the spatial resolution and iteration time step for accurate TLM numerical computations is suggested based on a simple frequency analysis. Copyright © 2003 John Wiley & Sons, Ltd.
Use of lossless transmission‐line segments and shunt resistors for TLM diffusion modelling
Authors: Gui Xiang 
Published: October 2003

AbstractIn diffusion modelling by means of the transmission‐line matrix (TLM) method, a nodal arrangement of using lossless transmission‐line segments and series resistors is almost exclusively adopted and is currently considered as a standard approach. In this paper, the use of shunt resistors instead of series resistors is shown to represent an equally valid configuration. As a starting point, we have derived the telegrapher's equation in its most general form for TLM modelling of diffusion processes. A general algorithm based on the shunt‐resistor TLM model for implementing a numerical solution of the diffusion equation in multiple dimensions is given. Fundamental analysis and calculated examples confirm that the alternative shunt‐resistor configuration does not exhibit the unwanted absorption effects suggested by a recent paper (Internat. J. Numerical Model.: Electronic Networks, Devices and Fields 2002; 15:261). Copyright © 2003 John Wiley & Sons, Ltd.
Computation of STM images of carbon nanotubes
Authors: Lambin P. , Márk G. I. , Meunier V. , Biró L. P. 
Published: October 2003

AbstractScanning tunneling microscopy (STM) is the only probing technique that allows for the investigation of both the topography and the electronic structure of carbon nanosystems at a subnanometer resolution. The interpretation of the STM images of carbon nanostructures involves complications that are normally absent in the study of planar crystalline surfaces. The complications typically appear from a number of quantum effects responsible for distortions in the microscope image of a nano‐object. Because of these difficulties, computer simulation plays an extremely important role in the analysis of experimental data. In the current article, we report on two theoretical approaches developed for aiding in the interpretation and understanding of the formation of the STM image of a nanotube: first, the quantum mechanical dynamics of a wave packet, which allows for the modeling of the flow of the tunneling current between a tip and a nanotube supported by a substrate; and, second, a tight‐binding perturbation theory that allows for the explicit calculation of realistic STM images and scanning tunneling spectra of carbon nanostructures. An atlas of computed STM images is provided for a series of 27 single‐wall nanotubes with diameter around 1.3 nm. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Further observations of projectile‐z dependence in target parameters of modified Bethe–Bloch theory
Authors: Porter L. E. 
Published: October 2003

AbstractSeveral studies of a systematic dependence on projectile atomic number (z) of the values of the two prominent target parameters of modified Bethe–Bloch theory have been published over the past 3 years. The target materials for which parameter values were extracted from stopping power measurements by analyses with modified Bethe–Bloch theory were initially the four organic (co)polymers—formvar, polyimide, polysulfone, and vyns—and the cobalt‐base alloy, havar. An additional (in press) study for the frequently utilized target materials, aluminum and copper, and for titanium and zinc targets, revealed considerable corroboration of the initially discovered trends. The scope of the investigation has been enlarged in the current study to include analyses of measurements with light projectiles of the stopping powers of 11 halogenated hydrocarbons, and with both light projectiles and heavy ions of the stopping powers of kapton (a polyimide), polycarbonate, havar, and nickel. The results of this, most recent, study are also generally corroborative of the previously established pattern of behavior of the two prominent parameters of modified Bethe–Bloch theory. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
A novel method for generating approximate wavefunctions
Authors: Weiner B. 
Published: October 2003

AbstractMolecular Hamiltonians are constituted by momentum operators (e.g., kinetic energy and interaction with electromagnetic radiation), local potential operators (e.g., electron–electron coulomb, electron–nucleus, and electron–external field interactions), and spin operators. In general, the effect of transformations that generate states from a reference state is to destroy this form. Here it is shown how one can generate all pure states by the action of a commutative semigroup of transformations that are diagonal in the space–spin coordinate representation that do not destroy this form and thus maintain the physical interpretability of effective Hamiltonians. Using such transformations, we formulate an approximation theory that has physical interpretation at all orders. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Internal energy and magnetic moment of three‐dimensional ferromagnets
Authors: Misra Anirban , Klein D. J. , Datta Sambhu N. , March N. H. 
Published: October 2003

AbstractThe unique relationship between the reduced internal energy and magnetic moment is investigated for a three‐dimensional ferromagnet on the basis of a many‐body k‐space spin‐wave solution of an anisotropic Heisenberg Hamiltonian of general site spin S. Spin‐wave interactions up through terms quartic in Boson creation and annihilation operators are considered. The three‐dimensional lattice on which the Hamiltonian is developed is in terms of the so‐called “bundle representation” for three independent axes as applicable to systems of orthorhombic and higher symmetry. The Hamiltonians considered are general enough to encompass models ranging from the ordinary (isotropic) Heisenberg Hamiltonian to the anisotropic Ising Hamiltonian, all for general values of S. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Unified quantum molecular dynamics method based on centroid molecular dynamics and semiempirical molecular orbital theory
Authors: Ohta Yasuhito , Ohta Koji , Kinugawa Kenichi 
Published: October 2003

AbstractWe have developed a unified quantum molecular dynamics method, in which the centroid molecular dynamics including the quantum effect of atomic nuclei is unified with the semiempirical molecular orbital calculation for the atomic configuration generated in the molecular dynamics. This unified method has successfully been applied to a couple of diatomic molecular systems for examining its performance. The method has yielded excellent agreement with exact quantum results and taken sufficiently short CPU time for practical use. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Inclusion of Rydberg orbitals in semiempirical calculations on excited states?
Authors: Head John D. 
Published: October 2003

AbstractSemiempirical methods, especially Zerner's INDO/S method, are well‐established tools for theoretically investigating the low‐lying valence excitations in large biologically important molecules. In recent years ab initio calculations have shown that low‐lying excited states arise from both valence and Rydberg states. Using experience from ab initio calculations we explore whether Rydberg orbitals can be successfully added to semiempirical procedures. The procedure, implemented in Zerner's INDO/S method, consists of adding a shell of Rydberg orbitals at a single center on the molecule. New integral approximations are introduced to take into account that a Rydberg orbital has a much greater radial extent than the valence basis functions and allow mixing between the valence and Rydberg excited states. Parameters for the Rydberg orbitals are obtained by fitting to the experimental vertical excitation energies for ethylene and benzene while keeping the original valence orbital parameters fixed. The procedure is then evaluated by examining the vertical excitation energies computed for t‐butadiene, all‐trans hexatriene, cyclobutadiene, pyrrole, and furan. Overall we obtain encouraging results suggesting that Rydberg orbitals can realistically be treated by a semiempirical procedure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Global optimization of SixHy at the ab initio level via an iteratively parametrized semiempirical method
Authors: Ge Yingbin , Head John D. 
Published: October 2003

AbstractPreviously we searched for the ab initio global minima of several SixHy clusters by a genetic algorithm in which we used the AM1 semiempirical method to facilitate a rapid energy calculation for the many different cluster geometries explored. However, we found that the AM1 energy ranking significantly differs from the ab initio energy ranking. To better guarantee locating the ab initio global minimum while retaining the efficiency of the AM1 method, we present an improved iterative global optimization strategy. The method involves two separate genetic algorithms that are invoked consecutively. One is the cluster genetic algorithm (CGA), mentioned above, to find the semiempirical SixHy cluster global minimum. A second and separate parametrization genetic algorithm (PGA) is used to reparametrize the AM1 method using some of the ab initio data generated from the CGA to form a training set of different reference clusters but with fixed SixHy stoichiometry. The cluster global optimization search (CGA) and the semiempirical parametrization (PGA) steps are performed iteratively until the semiempirical GA reparametrized AM1 (GAM1) calculations give low‐energy optimized structures that are consistent with the globally optimized ab initio structure. We illustrate the new global optimization strategy by attempting to find the ab initio global minima for the Si6H2 and Si6H6 clusters. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Computational prediction of relative group polarizabilities
Authors: Jin Ping , Brinck Tore , Murray Jane S. , Politzer Peter 
Published: October 2003

AbstractEarlier work has shown that molecular polarizabilities correlate well with the quantity V/IS,ave, where V is the volume of the molecule and IS,ave is the average value of the local ionization energy on its surface. We now extend this to group polarizabilities; we computed V/IS,ave for four common chemical groups (NO2, CH3, NH2, and OH) in a variety of molecules. The transferabilities of IS,ave, V, and V/IS,ave are examined, as well as the correlation between V/IS,ave and literature polarizabilities of CH3, NH2, and OH. This permits the value for NO2 to be predicted (α = 2.77 Å3). The dependence of IS,ave, and therefore V/IS,ave, upon the remainder of the molecule is discussed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Mechanism of phosphoryl transfer in kinases investigated by semiempirical calculations
Authors: Hutter Michael C. , Helms Volkhard 
Published: October 2003

AbstractThe reaction mechanism of the enzymatic phosphoryl transfer in active site model systems of three kinases has been studied previously by AM1 semiempirical molecular orbital calculations. The computed mechanism shows the synchronous shift of a proton to the transferred PO3 group in all our kinase model systems despite the chemical variety of the phosphoryl acceptors and the distinct differences of the associated energy profiles. Here, computed geometries are compared with X‐ray crystallographic data and results of density functional calculations. Further, the presence of the transition‐state analog aluminum fluoride was found to alter the protonation state of the phosphoryl acceptors. In combination with recent experimental studies we suggest that the concerted mechanism of phosphoryl transfer is common to all kinases. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Crystal orbital study of polycarbonyl
Authors: Podeszwa Rafał , Bartlett Rodney J. 
Published: October 2003

AbstractWe present crystal orbital calculations of polymeric carbon monoxide (polycarbonyl) by means of Hartree–Fock (HF), density functional theory (DFT), and second‐order many‐body perturbation theory [MBPT(2)] methods. The calculations are performed with improved integral evaluation routines. The results include optimized geometries obtained with HF and DFT methods and MBPT(2) correlation energies calculated at fixed geometry. The chain forms a zig‐zag of equidistant carbonyl groups. The results indicate the relative stability of polycarbonyl and may suggest the possibility of experimental detection of metastable forms of the polymer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Study of decoherence in a NMR quantum computer using tetrafluoropyridine
Authors: Tei Minaru , Mizuno Yoichi , Manmoto Yoshinori , Sawae Ryuichi , Takarabe Kenichi 
Published: October 2003

AbstractRecently, quantum algorithms have been realized on a quantum computer by using a nuclear magnetic resonance technique. The nuclear magnetic resonance quantum computer (NMR‐QC) consists of nuclear spins of molecules that are coupled by J‐coupling to each other and the nuclear spins take a role of quantum bits (qubits). In performing quantum algorithms on NMR‐QC, the decoherence effects are a key problem. We studied the decoherence effects in the four‐qubit NMR‐QC using the fluorine nuclear spins of tetrafluoropyridine molecules. The nitrogen nuclear spin in the tetrafluoropyridine molecule increases the transverse relaxation rate of nearby fluorine nuclear spins about 10 times because of its quadrupole moment. In this study we evaluated the decoherence effects in the NMR‐QC by utilizing controlled‐not quantum gates. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Interface structures of III–V semiconductor heterostructures
Authors: Kim Seong‐Gon , Kim Sungho , Shen Jun , Nosho B. Z. , Erwin S. C. , Whitman L. J. 
Published: October 2003

AbstractWe report first‐principles calculations of the electronic and geometric structure of the (110) cross‐sectional surfaces on InAs/GaSb superlattices and compare the results to scanning tunneling microscopy images of filled electronic states. We also study the atomic scale structure of (001) interface surfaces and the adsorption of deposited atoms on these surfaces to simulate the process occurring during the heterostructure growth. In both the predicted and measured images the InAs (110) surfaces appear lower than GaSb, a height difference we show is caused primarily by differences in the electronic structure of the two materials. In contrast, local variations in the apparent height of (110) surface atoms at InSb‐ or GaAs‐like interfaces arise primarily from geometric distortions associated with local differences in bond length. We further observed that both Ga‐ and Sb‐terminating (001) surfaces showed dimerization of surface atoms. Ga‐terminating (001) surfaces exhibited substantial buckling of surface atoms while Sb‐terminating (001) surfaces did not show appreciable buckling. The adsorption of arsenic atoms occurred preferably at the bridge sites between the dimerized Sb atoms on Sb‐terminating (001) surfaces. Indium atoms, on the other hand, were observed to have somewhat equal probabilities to be adsorbed at a few different sites on Ga‐terminating (001) surfaces. Our calculated energies for atomic intermixing indicate that anion exchanges are exothermic for As atoms on Ga‐terminating (001) interfaces but endothermic for In atoms on Sb‐terminating (001) interfaces. This difference may explain why GaAs interfaces are typically more disordered than InSb interfaces in these heterostructures. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Electronic polarization of 1H‐benzotriazole in water: Ground and first excited‐state dipole moments
Authors: Ludwig Valdemir , Coutinho Kaline , Borin Antonio Carlos , Canuto Sylvio 
Published: October 2003

AbstractSequential Monte Carlo and quantum mechanical calculations of the electronic polarization of the ground and first vertical excited states of 1H‐benzotriazole in water are made. Using statistically uncorrelated configurations and CASSCF ab initio calculations the increase in the ground and excited state dipole moments of 1H‐benzotriazole from gas phase to aqueous environment are obtained as 2.89 ± 0.10 and 2.75 ± 0.11 D, leading to total moments of 6.89 ± 0.10 and 6.40 ± 0.11 D, respectively. Structures are sampled using the statistical correlation interval obtained from the autocorrelation function of the energy and statistical convergence of the calculated dipole moments is shown. These water‐polarized dipole moments of 1H‐benzotriazole are used to obtain the solvatochromic shift of the first absorption transition. The resulting theoretical blue shift of 570 cm−1 for the strong and characteristic π → π* transition is in good agreement with the inferred experimental value of ∼700 cm−1. The use of the gas‐phase values of the dipole moments are useful for the qualitative understanding of the shift but the polarization of the solvent is required to achieve quantitative agreement. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
One‐ and two‐exciton migration dynamics of a dendritic molecular aggregate
Authors: Takahata Masahiro , Nakano Masayoshi , Yamada Satoru , Yamaguchi Kizashi 
Published: October 2003

AbstractThe two‐exciton dynamics in a dendritic molecular aggregate composed of monomers coupled with each other by the dipole–dipole interaction is performed to investigate the effect of two‐exciton states on the exciton migration using the master equation approach. Although the spatial unique feature of exciton migration from the periphery to the core in the one‐exciton model is also observed in the two‐exciton model, about 36% of such exciton migration is found to be carried out by the relaxation among two‐exciton states in the present model. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Time‐dependent density functional theory calculations of X‐ray absorption
Authors: Rehr J. J. , Ankudinov A. L. 
Published: October 2003

AbstractThere has been dramatic progress in recent years both in calculations and in the interpretation of X‐ray absorption spectra (XAS). Often an independent‐electron approximation with final state potentials is adequate. However, for soft X‐rays (i.e., energies less than about 1 keV) local field effects can be important. Such local fields arise from the dynamic screening of both the external X‐ray field and the coupling to the core hole created in the absorption process. These effects require a theory that goes beyond the independent‐electron approximation. We developed an efficient approach for treating such effects in molecules and solids based on a generalization of time‐dependent density functional theory (TDDFT), with a local approximation for the screening response. The approach has been implemented in our self‐consistent, real‐space Green's function code FEFF8 in terms of screened dipole transition matrix elements. Typical results are discussed for the XAS of the N4,5 edges of solid Xe and for the L2,3 edges of 3d transition metals. Our approach accounts for the deviations of the L3/L2 intensity branching ratio from the 2:1 value of the independent electron approximation. For the N4,5 edges of Xe, the approach also accounts for the observed fine structure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Derivation and efficient implementation of a recursion formula to calculate harmonic Franck–Condon factors for polyatomic molecules
Authors: Hazra Anirban , Nooijen Marcel 
Published: October 2003

AbstractWe present a simple derivation of a recursion formula for calculating harmonic Franck–Condon (FC) overlap integrals for polyatomic molecules. We also provide an efficient algorithm for computer implementation of the recursion formula. The algorithm resolves the problems associated with earlier implementations and has the following features: (1) It allows obtaining convergence of the series of FC overlap integrals to the degree desired (the measure of convergence is the sum of the FC factors, which is unity for the converged series); (2) the maximal number of quanta in the normal modes does not have to be specified a priori; (3) there is no computer memory bottleneck to do large FC calculations with many normal modes; (4) the algorithm uses binary trees to store data, thus making data retrieval fast and the algorithm highly efficient. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
n‐Electron problem and its formulation in terms ofk‐particle density cumulants
Authors: Kutzelnigg Werner 
Published: October 2003

AbstractApproaches to the solution of then‐electron problem in terms of the reducedk‐particle density matricesγkor their cumulantsλkare critically reviewed. The advantages of a cumulant‐based theory are outlined, especially its extensivity, which implies a connected‐diagram theorem. A perturbative analysis of the hierarchy ofk‐particle approximations, based on the irreducible contracted Schrödinger equations (ICSEk) (which are conditions for the stationarity of the energy), reveals that the three‐particle approximation is necessary to obtain the energy correct to the MP2 (second‐order Møller–Plesset) level. This disqualifies the naive use of thek‐particle hierarchy, in a linearly converging iterative scheme, as ineffective (compared, e.g., to coupled‐cluster theory). A promising alternative is, however, a quadratically convergent iterative scheme based on successive unitary transformations in Fock space. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Monte Carlo Wave Function (MCWF) approach to dissipative quantum systems interacting with a single‐mode quantized field
Authors: Nakano Masayoshi , Yamaguchi Kizashi 
Published: October 2003

AbstractWe investigate the quantum dynamics of a dissipative molecular system interacting with a single‐mode coherent field (with an initial average photon number 8) using the Monte Carlo wave function (MCWF) method. As quantum dissipation, we consider cavity relaxation (the dissipation of an internal single mode to outer mode) and molecular population relaxation and molecular coherent (phase) relaxation caused by nuclear vibration. In this study, we elucidate the effects of these dissipations on the unique quantum dynamic behaviors of this coupled system, e.g., collapse–revival behavior of Rabi oscillations, using the diagonal and off‐diagonal molecular density matrices. It is found that although slight cavity relaxation suppresses the revival of molecular population similarly to other relaxation effects with larger decay rates the cavity relaxation hardly suppresses the increase in the off‐diagonal molecular density matrix (representing the degree of coherency between the ground and excited states) in the quiescent region, the feature of which is related to the generation of the Schrödinger cat state, in contrast to molecular phase and population relaxations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003