Gradients in coupled-pair theories

by Pulay, Peter

The calculation of analytical gradients for coupled-pair wave functions is discussed. It is emphasized that gradients can only be efficiently evaluated if the CI coefficients minimize the total energy expression. Two CEPA versions are proposed which have this property. CEPA-F has fixed denominator shifts. CEPA-VAR is an approximation to CEPA-2: its denominator shifts are two-thirds of the pair correlation energies, and the energy formula is minimized with respect to the CI coefficients. Equations are presented for the derivatives of the localized orbitals which are needed in the localized form of CEPA-VAR.

Journal
Journal of Molecular Structure-Theochem
Volume
103
Year
1983
Start Page
57
ISBN/ISSN
2210-2728; 0166-1280
DOI
10.1016/0166-1280(83)85009-X