ISSN:0192-8651    

DOI:10.1002/jcc.540080402

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have performed large‐scale close coupling calculations of rotational‐to‐rotational energy transfer in HFHF collisions for the realistic potential energy surface of Brobjer and Murrell. We employ up to 525 angular terms in the expansion of the potential and up to 440 coupled channels in the rotational‐orbital basis set. The results for zero total angular momentum are well converged for relative translational energies up to over 0.6 eV, and they show extensive rotational e

ISSN:0192-8651    

DOI:10.1002/jcc.540080403

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

ISSN:0192-8651    

DOI:10.1002/jcc.540080404

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe theory of an implementation of the diabatic surface model within the Heitler–London valence bond approach is described. It is shown that theHL–VBwave function can be obtained from a Van‐Vleck transformation of anMC–SCFwave function which has been built from atom‐localized orbitals. This wave function is built from a superposition of two diabatic components, reactantlike and productlike. The transition structure is then obtained as the minimum of the seam of intersection of the diabatic surfaces and the algorithm for performing this constrained optimization is described. Several areas of application are also

ISSN:0192-8651    

DOI:10.1002/jcc.540080405

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractOur procedure for employing analytical gradients ofab initiopotential energy hypersurfaces in the description of centrifugally distorted molecules is applied for the first time to an asymmetric top, namely ozone. Both single determinantal (HF/6‐31G*) and analytically fitted multiconfigurational self‐consistent field surfaces were utilized. The focus of theHF/6‐31G* study is upon the centrifugal distortion pathway. Quartic centrifugal spectroscopic coefficients are obtained in both cases and are in reasonable agreement with exper

ISSN:0192-8651    

DOI:10.1002/jcc.540080406

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractUsing the dressed molecule picture of molecule radiation interactions (A.D. Bandrauk et al.,J. Chem. Phys.,79, 3256;80, 4926;83, 2840) one can deduce multiphoton processes (absorption, scattering, nonlinear optical properties, etc.) amplitudes from coupled second‐order differential equations with electronic surfaces and transition moments as input data obtainable from quantum chemical calculations. The present approach enables one to include in the calculationboundandcontinuumstates simultaneously by the use of appropriate boundary conditions for the numerical solutions of these coupled equations. In the case of weak radiative couplings, one recovers the usual Fermi‐Golden rule expressions for electronic absorption, raman scattering, etc. The method is thus quite general, bridging the weak field (traditional photochemistry) and the strong field (laser chemistry) regimes which are attainable with today's lasers. The numerical solutions of the coupled equations give us the stationary states of the molecule + radiation system, called dressed molecule. Preparation of the initial state can be mimicked in the coupled equations by an artificial channel method for processes involving a final‐state dissociation. Examples of such calculations will be presented in the diatomic Cl2for which severalab initioelectronic states and transition moments were avai

ISSN:0192-8651    

DOI:10.1002/jcc.540080407

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe implementation of the GAUSSIAN 82 system of quantum chemistry codes on the CDC Cyber 205 supercomputer required approximately 1 1/2 man years of effort. Idiosyncracies of the Cyber 205 architecture, operating system, and compiler in so far as they affect the conversion and operation of large quantum chemistry codes on the machine are described. While advantage has not been taken of the powerful vector processor, the high intrinsic speed of the scalar processor and the large virtual storage capacity of the Cyber 205 make it a very powerful research tool for computational chemistry. The impact of the GAUSSIAN 82/Cyber 205 combination on computational chemistry research at the University of Calgary is illustrated by brief descriptions of a range of applications from highly accurate calculations on small systems to semiempirical studies of large molecular aggregates. Complete geometry optimizations and harmonic frequency analyses, for the most part, have become routine.

ISSN:0192-8651    

DOI:10.1002/jcc.540080408

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractMonte Carlo simulation results are presented for lattice models of uniform stars (one branch point of functionalityf= 3), combs (two branch points, ƒ = 3,3) and brushes (two branch points ƒ = 3,4 and ƒ = 3,5). We estimate the critical exponent γ(ƒ), the ratiog(ƒ) = 〈S N2(ƒ)〉/〈S N2(1)〉 (where 〈S N2(ƒ)〉 is the mean‐square radius of gyration of a structure having ƒ branches andNmonomers), and the meansquare end‐to‐end branch lengths, as a function of the number and arrangement of branches. Comparisons with theoretical predictions and experimental data are made where possible, leading to a test of some predictions, and a suggesti

ISSN:0192-8651    

DOI:10.1002/jcc.540080409

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe graph‐theory derived model for the bonding topology in the globally delocalized polyhedral boranes B6H62−and B12H122−is evaluated by comparison of the energies of the core molecular orbitals with those obtained by the 1962LCAO‐MOextended Hückel calculations of Hoffmann and Lipscomb. Of particular interest is how well the complete graphsK6andK12used in the graph‐theory derived model approximate the bonding topologies of the unique internal orbitals (radial orbitals) of the octahedron and icosahedron, respectively. In the case of the B6H62−octahedron the single positive eigenvalue of theK6graph corresponds to the results from the extended Hückel calculations. In addition, the parameters from the latter calculations indicate a ratio of 0.625 for the overlap of the unique internal orbitals of the trans atom pairs relative to cis atom pairs as compared with unity implied by an unweightedK6graph. In the case of the B12H122−icosahedron the graph‐theory derived model is far less satisfactory since the single positive eigenvalue of theK12graph disagrees with the four bonding core molecular orbitals (an A1gand three triply degenerateT1umolecular orbitals) found by the extended Hückel calculations after removing the effect of the mixing of core and surface bonding orbitals corresponding to the same irreducible representations. However, this core‐surface orbital mixing raises the energy of the triply degenerateT1ucore molecular orbitals to antibonding levels so that the graph‐theory derived model fortuitiously gives correct skeletal electron counts for the regular icosahedron despite

ISSN:0192-8651    

DOI:10.1002/jcc.540080410

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractA new method for the solution of the vibronic Schrödinger equation is presented. The proposed approach allows the preservation of the concept of potential surfaces under inclusion of nuclear motion. The dynamical interaction of electrons and nuclei is partially included in the equation determining the potential surfaces. The corresponding electronic wave functions can be used as a basis for a generalized representation. Since the variation principle is involved for the determination of the potential surfaces, the proposed representation may be considered as a generalization of the adiabatic one. As a consequence the vibrational wave equation and the calculation of radiationless transition probabilities is simplified

ISSN:0192-8651    

DOI:10.1002/jcc.540080411

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY