Energy Derivatives of Correlated Wavefunctions: A Matrix Directed Approach (Dimagnesium)
Jasien, Paul Gerard
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https://hdl.handle.net/2142/70277
Description
Title
Energy Derivatives of Correlated Wavefunctions: A Matrix Directed Approach (Dimagnesium)
Author(s)
Jasien, Paul Gerard
Issue Date
1984
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
The appropriate expressions for obtaining the first derivative of the correlated Self-Consistent Electron Pair (SCEP) wavefunction are presented. The matrix directed, pair operator approach used within the SCEP formalism allows certain redundancies found in ordinary configurational-type correlated derivative calculations to be eliminated. Calculation of the first order changes in the molecular orbital coefficients via a Coupled Perturbed Hartree Fock procedure is essential in this formulation as in all other derivative CI techniques. Determination of these coefficients provides a means by which a transformation between the usual pair coefficient matrices of SCEP and their derivative counterparts may be effected. Since many of the matrix operators necessary in the derivative evaluation are necessarily constructed and stored in the energy evaluation, calculational time is minimized. Demonstration calculations using this method are performed for electric field derivatives. Results comparing expectation values versus analytic derivative values are presented for HF and CO as a function of basis set and internuclear distance.
The results of ab initio calculations at both the SCF and correlated levels are presented for a number of disubstituted dimagnesium molecules as well as selected beryllium and calcium analogues. These results predict the stability under isolated conditions of disubstituted, metal-metal bonded species with the metal in a formal +I oxidation state. Further theoretical investigations comparing energy barriers of one and two magnesiums reacting with HF and HCl reveal comparable barriers for insertion, however radical formation appears to be feasible only in the case of a two magnesium reaction site.
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