Analytic gradients for the spin-conserving and spin-flipping equation-of-motion coupled-cluster models with single and double substitutions

Sergey V Levchenko; Tao Wang; Anna I Krylov

doi:10.1063/1.1877072

Analytic gradients for the spin-conserving and spin-flipping equation-of-motion coupled-cluster models with single and double substitutions

J Chem Phys. 2005 Jun 8;122(22):224106. doi: 10.1063/1.1877072.

Authors

Sergey V Levchenko¹, Tao Wang, Anna I Krylov

Affiliation

¹ Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA.

PMID: 15974650
DOI: 10.1063/1.1877072

Abstract

Analytic gradient expressions for the spin-conserving and spin-flipping equation-of-motion coupled-cluster models with single and double substitutions are derived using a Lagrangian approach for the restricted and unrestricted Hartree-Fock references, both for the case of all orbitals being active in correlated calculations and for the frozen core and/or virtual orbitals. Details of the implementation within the Q-CHEM electronic structure package are discussed. The capabilities of the new code are demonstrated by application to cyclobutadiene.