bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some solutions in the graph theory of alternant benzenoids
Authors: Hall George G. 
Published: January 2005

AbstractA new formulation of the eigenvector equations for certain polymeric molecules is given. The electronic bands for the infinite molecules are deduced. For the finite molecules, the use of ghost molecules allows an exact specialization of the infinite to the finite eigenvector equations. The complete solution of the equations depends on the solution of a simple transcendental equation. Approximate solutions of this equation are given that bracket the accurate solutions so that, for molecules with many repeated moieties, the approximations become good. The general theory is illustrated by applications to the chrysene series and to the polyphenyls. © 1993 John Wiley & Sons, Inc.
The fundamental syntopy of quasi‐symmetric systems: Geometric criteria and the underlying syntopy of a nuclear configuration space
Authors: Mezey Paul G. , Maruani Jean 
Published: January 2005

AbstractPoint symmetry is a discrete concept; A nuclear configuration for a given stoichiometry either has or has not a particular point symmetry. By contrast, both static and dynamic properties of actual molecules exhibit continuous features. Using the formalism of fuzzy‐set theory, we had previously proposed the concept of syntopy as a continuous extension of the symmetry concept for quasi‐symmetric systems: This was based on an energetic criterion taking into account the energy costs of nuclear rearrangements. This extension of symmetry was necessarily dependent on the considered electronic state: For a given geometric arrangement of the nuclei, the energy cost of some rearrangement is dependent on the actual potential surface, that is, on the electronic state, in the Born–Oppenheimer approximation. In the extension of the syntopy model reported in the present work, we consider a syntopy criterion that is common to all electronic states. The syntopy thus defined—called the fundamental syntopy of the reduced nuclear configuration space—is independent of the potential surface and of the electronic state: It is defined only in terms of a geometric condition, which makes it more appropriate to rationalize mesoscopic structures. This new syntopy model provides a connection between all possible syntopies generated by the various potential‐energy surfaces supported by the considered family of atomic nuclei. © 1993 John Wiley & Sons, Inc.
On the applicability of a nonlinear Schrödinger equation to the determination of rate constants in Kramers' theory of chemical reactions
Authors: Schuch Dieter 
Published: January 2005

AbstractIn 1940, Kramers derived an expression for the rate constant of chemical reactions in viscous media. In this theory, chemical reactions are modeled as Brownian processes in the presence of potential barriers. The derivation of the rate constant is based on the solution of the Smoluchowski equation, a Fokker–Planck‐type equation in position space. Kramers' theory has been confirmed for reactions in systems ranging from nuclear processes to biochemical problems. The reaction rate can be obtained from the diffusion currents appearing in the Smoluchowski equation. A Smoluchowski‐type equation in position space, similar to the one applied by Kramers, has been used to find a nonlinear Schrödinger equation (NLSE) for dissipative, frictionally damped systems, taking into account wave‐particle duality. For several potentials, the NLSE can be solved exactly, and analytic expressions for the currents, appearing in the Smoluchowski equation and necessary to determine the rate constants, can be obtained. These currents are not only stationary, but can also be time‐dependent. It will be shown that, essentially, the determination of the time‐dependence of the currents can be reduced to the solution of Newton‐type equations of motion. © 1993 John Wiley & Sons, Inc.
Perturbation expansions, symanzik scaling, and padé‐type approximants: The anharmonic oscillator problem
Authors: Chandra A. K. , Bhattacharyya K. 
Published: January 2005

AbstractThe problem of representing an observable F(z) in the Padé scheme from its formal perturbative (Taylor) expansion in z is considered. It is demonstrated how the representation could be improved by incorporating in a simple manner, in the course of constructing such approximants, the knowledge of asymptotic (z → ∞) power‐law behavior of F(z). Comparison with the usual approximants is made with a thorough numerical survey on error estimates and variations of error with z, input information, and quantum number. Spectacular performance of the new strategy is exemplified. Test calculations chiefly involve various properties of the first five eigenenergy states of the quartic anharmonic oscillator system. A few consistency requirements, including the virial theorem, are also studied. © 1993 John Wiley & Sons, Inc.
Husimi representation for stationary states
Authors: Harriman John E. , Casida Mark E. 
Published: January 2005

AbstractThis paper considers a Husimi representation of quantum mechanics in which the (stationary) state of a system or ensemble is described by a Husimi function and an observable is described by a phase space function or distribution such that the expectation value of the observable is given by an integral over phase space of the product of that function or distribution and the Husimi function. The density matrix, Wigner function, and Husimi function are considered to be alternative ways of describing the state of a system or ensemble, and methods of recovering the Wigner function or density matrix from the Husimi function are discussed. The classical limits of the Wigner and Husimi functions and of the relationship between them are considered. © 1993 John Wiley & Sons, Inc.
Coupling coefficients for systems with two open electronic shells: Transition metal ions with pM dN configuration
Authors: Plakhutin B. N. , Arbuznikov A. V. , Trofimov A. B. 
Published: January 2005

AbstractWe derived the necessary conditions to which the vector coupling coefficients (VCC) amn and bmn, describing atomic L, S‐multiplets of pMdN and dNs1 configurations (1 ⩽ N ⩽ 9, 1 ⩽ M ⩽ 5), should satisfy. It is shown that for two‐open‐shell systems under consideration the unknown VCC should satisfy not only usual restrictions resulting from the spheric symmetry, but also some additional equation introduced in the present paper in the form of a postulate. VCC obtained were used for the ab initio calculations (by the general SCF coupling operator method) of several transitionmetal atoms and ions with electronic configurations 3d14p1, 3p43d3, and 3p53d3. To check the presented theory, we carried out a detailed comparison between these results and analogous data, obtained by the atomic Roothaan‐Hartree‐Fock method [2]. © 1993 John Wiley & Sons, Inc.
Unrestricted Hartree–Fock method for infinite systems with antiferromagnetic array: Analysis of antiferromagnetic state of trans‐polyacetylene
Authors: Yoshizawa Kazunari , Ito Akihiro , Tanaka Kazuyoshi , Yamabe Tokio 
Published: January 2005

AbstractAn improved unrestricted Hartree–Fock (UHF) crystal orbital method for infinite one‐dimensional systems having antiferromagnetic spin array is presented. This variational version of the UHF method is composed of two steps of self‐consistent‐field (SCF) calculations. The second SCF equation is to be solved using the canonical transformation between specific crystal orbitals around the Fermi level of the first conventional SCF solution. The energy gain and the forbidden band gap (correlation gap) associated with the hypothetical antiferromagnetic state of trans‐polyacetylene are examined as an example. © 1993 John Wiley & Sons, Inc.
Time scales and other problems in linking simulations of simple chemical systems to more complex ones
Authors: Clementi Enrico , Corongiu Giorgina , Estrin Dario , Hollauer Eduardo , Stradella Omar G. 
Published: January 2005

AbstractWe shall start with very small systems like H2 and H3, computed with very accurate methods (Hylleraas–CI) or atomic systems up to Zn with accurate methods (CI), then move to more complex ones, like C60, but now with somewhat less accurate methods, specifically Hartree–Fock with density functionals, the latter for the correlation energy but not for the exchange energy. For even more complex tasks like geometry optimization of C60, we have resorted to even simpler and parametrized methods, like local density functionals. Then, we could use quantum mechanics either to provide interaction potentials for classical molecular dynamics or to directly solve dynamical systems, in a quantum molecular dynamics approximation. Having demonstrated that we can use the computational output from small systems as input to larger ones, we discuss in detail a new model for liquid water, which is borne out entirely from ab initio methods and nicely links spectroscopic, thermodynamics, and other physicochemical data. Concerning time scales, we use classical molecular dynamics to determine friction coefficients, and with these we perform stochastic dynamic simulations. The use of simulation results from smaller systems to provide inputs for larger system simulations is the “global simulation” approach, which, today, with the easily available computers, is becoming more and more feasible. Projections on simulations in the 1996–1998 period are discussed, new computational areas are outlined, and a N4 complexity algorithm is compared to density functional approaches. © 1993 John Wiley & Sons, Inc.
4‐Currents in relativistic quantum chemistry
Authors: Avery John , Antonsen Frank , Shim Irene 
Published: January 2005

AbstractSome topics in relativistic quantum chemistry are reviewed with special emphasis on 4‐currents and 4‐potentials. It is shown that, both in molecular quantum theory and in solid‐state physics, calculations can include relativistic and magnetic effects by means of 4‐currents without an excessive increase in complication, provided that 4‐component Dirac spinors are used rather than the Pauli approximation. © 1993 John Wiley & Sons, Inc.
Looking at atomic orbitals through fourier and wavelet transforms
Authors: Fischer Patrick , Defranceschi Mireille 
Published: January 2005

AbstractSolutions of Hartree–Fock equations expressed as Gaussian functions are studied in various spaces: position, momentum, and position–momentum spaces. The use of the wavelet transform allows one to visualize position and momentum characteristics of atomic orbitals on the same drawing. A complementary viewpoint is then obtained on top of usual position and momentum representations. Applications to Gaussian “atomic” orbitals modeled as one‐dimensional functions are performed. © 1993 John Wiley & Sons, Inc.
Challenges to computational quantum chemistry from contemporary advances in polyatomic molecular electronic spectroscopy
Authors: Kasha Michael , Parthenopoulos Dimitri , Dellinger Barry 
Published: January 2005

AbstractMolecular electronic spectroscopy featuring intramolecular proton transfer and twisted intramolecular charge transfer poses a whole new range of problems for computational quantum chemistry. The development of the four‐level laser based on the intramolecular proton‐transfer focuses on the subtleties of the interaction of the singlet and triplet electronic state manifolds of the two different tautomeric species. Examples are given of the sensitive variation of proton‐transfer fluorescence with chemical substitution. A competing excitation channel is shown to exist when internal molecular torsion couples with sudden polarization to yield a twisted intramolecular charge transfer configuration. In such systems, three competing fluorescences can be observed. Several electronic puzzles will be presented that can provide fertile territory for quantum chemical computations. © 1993 John Wiley & Sons, Inc.
Theoretical treatment of electron capture processes for closed‐ and open‐ shell systems
Authors: Bacchus‐Montabonel M. C. , Amezian K. 
Published: January 2005

AbstractA full theoretical treatment of electron capture processes using ab initio configuration interaction methods within a semiclassical collisional formalism has been developed. An application to closed‐ and open‐shell systems is presented on the example of oxygen‐ion/He collisions. © 1993 John Wiley & Sons, Inc.
The molecular simulation approach to complex hydrodynamics
Authors: Mareschal M. , Kestemont E. , Mansour M. Malek 
Published: January 2005

AbstractWe present here some recent results obtained in the direct simulation of nonequilibrium fluids. First, the transition to convection is studied by means of a hard‐disk model with the appropriate boundary conditions. The quantitative agreement between molecular dynamics and Navier–Stokes hydrodynamics is an impressive argument in favor of the hydrodynamic modeling down to atomic scales, even in nonequilibrium states. Next, the Rayleigh–Brillouin spectrum of a hard‐sphere fluid subjected to a temperature gradient is presented. The simulation is used as a quantitative test of the “Landau–Lifshitz” hypothesis concerning the amplitude of the fluctuating hydrodynamic fluxes, extended to nonequilibrium. Finally, a short description of shock waves in a dilute system is given and the discrepancy between the molecular simulations and the continuum approach is further discussed. We conclude by some remarks concerning the perspectives in nonequilibrium fluids offered by the development of large‐scale computers. © 1993 John Wiley & Sons, Inc.
Ab initio studies of crystal field effects. VII. Structure of 2,3‐diketopiperazine using a 13‐molecule cluster, a calculation involving 1092 basis functions
Authors: Peeters Anik , Van Alsenoy C. , Lenstra A. T. H. , Geise H. J. 
Published: January 2005

AbstractThe structure of 2,3‐diketopiperazine in a crystal phase (P21/c), modeled by a 13‐molecule cluster surrounded by point charges, was completely optimized using standard gradient procedures. The (ab initio) MIA approach was used to perform the SCF step, which using a 4‐21G basis set, involves calculations using 1092 basis functions. Results are in very good agreement with experimental (X‐ray) data, in contrast to a previous study in which a model was used consisting of only point charges. © 1993 John Wiley & Sons, Inc.
The structure of n‐fold negatively charged C60 (n = 1, 2,…,6)
Authors: Hutter Jürg , Peter Lüthi Hans 
Published: January 2005

AbstractRestricted Hartree–Fock calculations were performed to optimize the structure of C60 and its negatively charged ions. The length of the short bond was found to increase lineraly with the charge, whereas the longer bond steadily decreases, resulting in a difference of only 0.0266 Å between the two bond types. Icosahedral symmetry was retained in all calculations. The state with the highest spin multiplicity is calculated to be the lowest in energy for all ions. © 1993 John Wiley & Sons, Inc.
Cluster‐size convergence of some physical parameters of bare (Nin) and CH3‐Chemisorbed (CH3Nin) nickel (111) clusters: An ab initio study
Authors: Bureau Christophe , Defranceschi Mireille , Delhalle Joseph 
Published: January 2005

AbstractHartree–Fock calculations of the molecular geometry and electronic properties (ionization potentials) of bare Nin clusters (n = 3, 7, 13, and 25) and nickel clusters bearing a chemisorbed CH3 radical are reported. A basis of double‐zeta quality on light atoms including carbon and a model core potential along with double‐zeta plus polarization auxiliary basis set for nickel atoms have been used. Computed properties serve to assess cluster‐size convergence when nickel atoms core electrons are described with [1s–3d] pseudopotentials. In spite of their simplicity, results with these potentials are in good agreement with previously reported theoretical and experimental data on seven‐atom clusters. This suggests that the cluster‐model approach to surface bonding using simple pseudoopotentials can lead to meaningful results and tractable computationl times when applied to larger chemisorbed organic molecules. Thus, this approach may be adequate to help find out direct experimental evidence of the interfacial bonding for grafted structures obtained under cathodic electropolymerization of acrylonitrile on nickel surfaces. © 1993 John Wiley & Sons Inc.
Polarization correction of the electrostatic potential for aromatic compounds: Study of the nucleophilic attack
Authors: Dive G. , Dehareng D. 
Published: January 2005

AbstractThe electrostatic potential (EP) and the polarization correction (PL) on the (EP) were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level within two basis sets: 6‐31G** and MINI‐1. One calculation was performed using the polarized MINI‐1** basis set. The quantity total interaction energy (TEH) defined as −EP + PL can be used as an indicator of the nucleophilic attack preferential position. By reference to 6‐31G**, MINI‐1 provides very satisfactory results. Moreover, the MINI‐1** results are very similar to the MINI‐1 ones. It appears that −EP does not provide a reliable tool to study the nucleophilic attack susceptibility, whereas TEH seems to be very well adapted for this kind of approach. © 1993 John Wiley & Sons, Inc.
Preliminary theoretical study of perfluorodimethyl ether and its protonated form
Authors: Fontaine Michèle , Delhalle Joseph , Defranceschi Mireille , Lécayon Gérard , Boissel Jacques 
Published: January 2005

Abstract3‐21G RHF calculations on (CF3)2O and (CF3)2OH+ molecules are carried out to assess the changes induced in the molecular properties of ether links in poly (perfluoro ethers) interacting with acid sites at contact surfaces. Geometry of the species, vibrational frequencies, proton affinity, and energetics of the (CF3)2OH+ fragmentation provide a preliminary basis to understand problems raised by lubricant degradation. © 1993 John Wiley & Sons, Inc.
Ab initio study of the electronic properties of potential antagonists of the glycine receptor: 1. Transition state of the 2‐pyridone · H2O/2‐hydroxypyridine · H2O tautomeric equilibrium
Authors: Michel Andrég. , Trudel Yolaine , Dion Claude 
Published: January 2005

AbstractGlycine receptor substrates are molecules potentially involved in tautomerism phenomena. This study is expected to provide information that might help understand their intrinsic reactivities; such physicochemical data would allow us to establish predictive models in a search for better antagonists. Ab initio molecular orbital studies, using 3‐21G and 6‐31G* basis sets, are reported for the tautomeric equilibrium of 2‐pyridone · H2O/2‐hydroxypyridine · H2O. The geometry of the transition state has also been optimized. The results show the important effect of the water molecule through the formation of hydrogen bonds. This system will be used as a prototype for the design of antagonists of the glycine receptor, a potential site for the action of new antiepileptic drugs and compounds preventing ischemic brain damage. © 1993 John Wiley & Sons, Inc.
Theoretical evaluation of atomic charges to be integrated into conformational analyses of neutral lipids
Authors: Culot Christine , Dory Magdalena , Durant Francois , Vercauteren Daniel P. 
Published: January 2005

AbstractConformational analyses of large molecules as fatty acids and triglycerides are usually amenable by molecular mechanics. A correct evaluation of the electrostatic energy term is thus crucial in determining reliable results. In this contribution, we have considered the most abundant fatty acids in biomembranes, i.e., lauric, stearic, oleic, and elaidic acid, and the corresponding triglycerides, i.e., trilaurin, tristearin, triolein, and trielaidin, and estimated the Mulliken and potential‐derived charges both at the semiempirical AM1 and ab initio HF MO STO‐3G level. Atomic charges obtained by the Mulliken population analysis do not take into account the full geometry of the molecule. On the contrary, the change of conformation, due to different chains length or the presence of a trans or cis double bond, greatly influences the repartition of the potential‐derived charges. A systematic comparative analysis shows that charges calculated by AM 1 are not suitable because as they do not reproduce potential‐derived charges obtained by ab initio. © 1993 John Wiley & Sons, Inc.
Ab initio rotational constants of interstellar species: Cyanoacetylene hydrogenated derivatives
Authors: Arnau Arturo , Silla Estanislao , Tuñón Iñaki 
Published: January 2005

AbstractBy means of ab initio calculations, the rotational constants and dipole moments of HnC3N (n = 1, 3, 5, 7, and 9) species have been calculated at the HF / 6‐31G* level of theory. Selected cases have been also calculated at the MP2/6‐31G* level and the influence of calculation level on rotational constant values is briefly discussed. Some of these species were discovered in the interstellar medium, while others have still not been detected there, although their existence is very probable. The results given here could help in their detection. © 1993 John Wiley & Sons, Inc.
Harmonic oscillator tensors. II. angular momentum expressions of matrix elements of vibrational operators
Authors: Palting Pancracio 
Published: January 2005

AbstractThe spatial symmetries of the harmonic oscillator and the recently found irreducible tensors constructed from the associated annihilation and creation operators are exploited to obtain new expressions for the elements of the matrix representatives of several examples of vibrational operators. Since all vibrational operators are expressible in terms of the irreducible tensors, their matrix elements reflect the angular momentum symmetry inherent in them, for the results derived here are in terms of the Clebsch–Gordan coefficients and the isoscalar factors that arise from the couplinig rule of the irreducible tensors. Familiarity with the mathematical properties of these quantities derived from the elementary theory of angular momentum facilitates the evaluation of many vibrational operators that may be of importance in the study of potentials in this basis. In particular, it is shown that the nonvanishing of matrix elements is governed by a law of conservation of angular momentum along the axis of quantization of the nondegenerate harmonic oscillator. © 1993 John Wiley & Sons, Inc.
Polystyrene models. III. modeling backbone/side‐group interactions by an ab initio study of 2,4‐diphenylpentane
Authors: Lagowski J. B. , Vancso G. J. 
Published: January 2005

AbstractThe Structure and the energy of the stable conformations of the two possible stereochemical configurations of 2,4‐diphenylpentane are obtained using the ab initio molecular orbital theory. The objective was to mimic the possible structures and determine the corresponding energies of the dyads of syndiotactic and isotactic polystyrene and, consequently, to study the interactions between the phenyl groups. The results of complete geometry optimization showed significant changes in geometrical parameters compared with those expected from the ideal hydrocarbon structure. The steric strain is most pronounced in some of the gauche conformations where large (approximately 40°) distortions of the backbone torsional angles and/or simultaneous phenyl group rotations in the range of 30°–40° away from its global minimum position may occur. In addition to the discussion of the geometrical parameters, the corresponding dipole moments are also calculated and differences related to the various structures and discussed. © 1993 John Wiley & Sons. Inc.