摘要:

AbstractSmall Sinand Alnclusters (n= 3–10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For eachn, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with availableab initiocalculationsdorbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three‐dimensional structures rather than two‐ or one‐dimensional structures, except forn= 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most‐stable structures. Ionization potentials,HOMO‐LUMOenergy differences, binding energies per atom, and average atomic valencies ar

ISSN:0192-8651    

DOI:10.1002/jcc.540090802

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this article, a modification of a procedure proposed by Zirrilliet al.for solving nonlinear equations is presented. The method permits the computation of minima and saddle points of energy functionals. The Müller‐Brown test potential and the quantum chemical description of some proton transfer reactions are given as exampl

ISSN:0192-8651    

DOI:10.1002/jcc.540090803

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractMonte Carlo statistical thermodynamic computer simulations are reported for several clusters Fe+(H2O)nat different temperatures and for a dilute aqueous solution of Fe+at 298 K. The energy of each configuration has been calculated in the pairwise additivity approximation using the MCY potential for the water–water interaction and anab initioanalytical potential built by us for the Fe+–H2O interaction. Energy and structural analysis of the generated configurations lead to the prediction of a coordination number of six for the first hydration shell of the Fe+ion, both in clusters and in dilute solution. Finally, the variation in the distance to the Fe+ion of the energy and orientation of water molecules in the solution are discus

ISSN:0192-8651    

DOI:10.1002/jcc.540090804

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe accuracy and applicability of the finite‐element method of the higher order interpolation functions to the one‐dimensional Schrödinger equation were examined. When the fifth‐order Lagrange and Hermite interpolation functions were used as the basis functions, practically exact solutions were obtained for all eigenvalues of several model potential energy functions. It was demonstrated that the appropriate analytical integration over the potential energy function within each element is important in the matrix element evaluation. The accuracy of the method was examined for the potential functions with a double minimum, which has a large classically forbidden region. The method was also applied to evaluate the Franck‐Condon factors of the transitions between the 11Σ g+and 21Σ u+states of Na2; the latter state having a double minimum in its potential e

ISSN:0192-8651    

DOI:10.1002/jcc.540090805

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe possible Cs, C2v, and C∞vstructures of AlO2corresponding to the two lowest electronic states which dissociate into the neutral Al(2P) and O2(3Σg−) fragments have been investigated at theab initioself‐consistent field (SCF) and CI levels using nonempirical pseudopotentials. The most stable structure corresponds to a C2vsymmetry in the2A2electronic state. However, this structure presents the three‐center three‐electron Hartree‐Fock instability and CASSCF calculations were necessary to unequivocally characterize it as true minimum. Moreover, only another stable structure, of C2vgeometry, was found to be a minimum, corresponding to a low‐lying excited state of2A1symmetry. The optimized C∞vstructures were not minima on the corresponding potential energy surfaces and no evidence of any stable Csstructure was found. Calculating values are compared with the different experimental data obtained from the reaction of Al and O2in frozen ga

ISSN:0192-8651    

DOI:10.1002/jcc.540090806

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe determination of the vibration‐rotation eigenvalues (for an electronic state of a diatomic molecule) is done using various algorithms, where the differential equationy″ +f(r)y= 0 (with given initial valuesyoandy′oat an originro) is to be integrated, that is, to be replaced by a “convenient” difference equation (DE). The best known are those of: Numerov (N), Runge‐Kutta (RK), and the Taylor series expansion (TS). Each algorithm is commonly associated with an “appropriate” DE, and the conventional comparisons of algorithms and/or DE are often misleading. This work compares different DE used in the same algorithm for the same potential and with the same tests. It considers the mentioned conventional DE, and three nonconventional ones: Hajjet al.(HKN) [J. Comp. Phys.,16, 150 (1974)], Cash and Raptis (CR) [Comput. Phys. Commun.,32, 299 (1984)], and Kobeissi “integrals superposition” (IS) [J. Phys. B,15, 693 (1982)]. A convenient test of these DE is presented and applied. It is shown that: (i) if ϵ is the average error by using Numerov DE, it is of 4ϵ for RK, 2ϵ for TS, ϵ × 10−3for HKN, 4ϵ × 10−4for CR and ϵ × 10−6for IS; (ii) if τ is the average computing time by using Numerov DE, it is of 2.9τ for RK, 3.4τ for TS, 1.5

ISSN:0192-8651    

DOI:10.1002/jcc.540090807

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA force field has been developed for use in MM2 calculations of geometric and energy data for linear peroxides R1OOR2and tested in some of them (R1, R2= H, Me, Et, Pri, But). The field obtained yield results that agree considerably better with experimental andab initiodata than those afforded by the only set of estimated parameters hitherto avai

ISSN:0192-8651    

DOI:10.1002/jcc.540090808

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractWe describe a simple and rapid algorithm for generating data structures and starting coordinates of polynucleotides for potential energy calculations. The algorithm is tailored to investigations in cartesian coordinate, rather than dihedral angle, space. First, instead of a tree structure for molecular design, we set up a helix from a simple list of bonds for the basic DNA subunits (sugar, phosphate, and bases). Second, instead of using successive transformations to obtain a set of coordinates in one reference frame, we apply a simple “matching” routine to patch DNA subunits. Third, we avoid ring closure and geometry optimization by allowing deviations from equilibrium values only for PO3′ bond lengths and O5′PO3′ bond angles at the residue connection sites. A double‐stranded helix is constructed from duplex building blocks (2 hydrogen‐bonded nucleotides) which are in turn built from the basic structural units. Every building block is constructed from two sets of geometric variables: {α, β, γ, χ,P, τmax}, one for each strand. The building blocks are then assembled into a helix by using the 6 rigid body transformations {Δx, Δy, Δz, ΘROLL, ΘTILT, ΘTWIST}. For cartesian space programs, generating starting coordinates by this procedure is particularly useful as an alternative to using actual crystal structure coordinates. After describing the algorithm in detail, we illustrate how it was used to generate modelA,B, andZDNA helices. We conclude by suggesting how the algorithm can be used to pursue a build‐up technique and to set up a wide range of starting conformations in the goal of l

ISSN:0192-8651    

DOI:10.1002/jcc.540090809

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe multiple scattering Xα(R) method with the scaling parameter α expressed as a function of the internuclear distance is applied to the Li2, N2, and F2molecules. Compared with the results obtained by the Xα method, the calculated Xα(R) equilibrium distances are smaller, the total energies are lower, and the dissociation energies are lar

ISSN:0192-8651    

DOI:10.1002/jcc.540090810

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA method has been developed which uses a rapid connectivity‐based calculation to give a reasonable approximation of CNDO σ and π charges for most carbons in saturated and unsaturated hydrocarbons. In this calculation an appropriately parameterized Del Re method is used to calculate the σ charges, and if the molecule is unsaturated, these charges are used to modify the diagonal elements in a Hückel matrix, reducing the normally exaggerated π charges. The CNDO charges are obtained from “single point” calculations, using optimized geometries derived from molecular mechanics. The Del Re/Hückel method is most reliable where steric and hyperconjugative effects

ISSN:0192-8651    

DOI:10.1002/jcc.540090811

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY