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  • 1
    ISSN: 1432-2234
    Keywords: Variational ; Non-variational ; Configuration interaction ; Diatomic molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The internally contracted multiconfiguration-reference configuration interaction (CMRCI) method and several non-variational variants of this method (averaged coupled pair approximation (ACPF), quasidegenerate variational perturbation theory (QD-VPT), linearized coupled pair many electron theory (LCPMET)) have been employed to compute potential energy functions and other properties for a number of diatomic molecules (F2, O2, N2, CN, CO) using large basis sets and full valence CASSCF reference wavefunctions. In most cases the variational CMRCI wavefunctions yield more accurate spectroscopic constants than any of the employed non-variational methods. Several basis sets are compared for the N2 molecule. It is found that atomic natural orbital (ANO) contractions led to significant errors in the computedr e , ω e , andD e values.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1473-1483 
    ISSN: 0192-8651
    Keywords: geometry optimization ; DIIS optimization algorithm ; Hessian ; natural internal coordinates ; rational function ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Various geometry optimization techniques are systematically investigated. The rational function (RF) and direct inversion in the iterative subspace (DIIS) methods are compared and optimized for the purpose of geometry optimization. Various step restriction and line search procedures are tested. The model Hessian recently proposed by Lindh et al. has been used in conjunction with different Hessian update procedures. Optimization for over 30 molecules have been performed in Z-matrix coordinates, local normal coordinates, and curvilinear natural internal coordinates, using the same approximations for the Hessian in all cases. The most effective and stable procedure for optimization of equilibrium structures was found to be the DIIS minimization in natural internal coordinates using the BFGS update of the model Hessian. Our method shows faster overall convergence than all previously published methods for the same test suite of molecules.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1473-1483, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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