Multireference CI Gradients and MCSCF Second Derivatives

A set of simple and efficient formulas for the calculation of multireference CI gradients and MCSCF second derivatives is presented. The CI gradient formalism is extended to include a general class of references in the CI. This extension is necessary for the calculation of gradients for a commonly e...

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Bibliographic Details
Main Authors: Lengsfield,Byron H , III, Saxe,Paul J, Adams,George F, Page,Michael J
Format: Report
Language:English
Subjects:
ASH43
COMPUTATIONS
DERIVATIVES(MATHEMATICS)
FORMULAS(MATHEMATICS)
GRADIENTS
HARTREE FOCK APPROXIMATION
INTEGRALS
MOLECULAR ORBITALS
PE61102A
PERTURBATIONS
Quantum Theory and Relativity
WAVE FUNCTIONS
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Description
Summary:A set of simple and efficient formulas for the calculation of multireference CI gradients and MCSCF second derivatives is presented. The CI gradient formalism is extended to include a general class of references in the CI. This extension is necessary for the calculation of gradients for a commonly employed class of CI wavefunctions for which the reference configurations are selected from a generalized CAS MCSCF wavefunction. In addition, we report the first general multireference CI gradient calculations. The calculations are for the reaction Be + H2 yields BeH2 constrained to C2v symmetry. Structures of the reactant and transition state and the activation energy calculated at the selected reference CI level compare favorably to the full second order CI results. MCSCF second derivatives are found to be useful for the optimization of the CI structures. (Author)