Quasidiabatic states described by coupled-cluster theory

Takatoshi Ichino; Jürgen Gauss; John F Stanton

doi:10.1063/1.3127246

Quasidiabatic states described by coupled-cluster theory

J Chem Phys. 2009 May 7;130(17):174105. doi: 10.1063/1.3127246.

Authors

Takatoshi Ichino¹, Jürgen Gauss, John F Stanton

Affiliation

¹ Department of Chemistry and Biochemistry, Institute for Theoretical Chemistry, The University of Texas at Austin, Austin, Texas 78712, USA.

PMID: 19425767
DOI: 10.1063/1.3127246

Abstract

In an attempt to expand the utility of the model Hamiltonian technique developed by Koppel, Domcke, and Cederbaum (KDC) [Adv. Chem. Phys. 57, 59 (1984)], an ansatz for quasidiabatic wave functions is introduced in the framework of equation-of-motion coupled-cluster (EOM-CC) theory. Based on the ansatz, the theory for the analytic first derivative of the off-diagonal element of the quasidiabatic potential matrix is developed by extending the theory for the analytic gradient of the EOM-CC energy. This analytic derivative is implemented for EOM-CCSD (singles and doubles approximation) calculations of radicals subject to pseudo-Jahn-Teller and Jahn-Teller interactions. Its applicability in construction of the KDC quasidiabatic model potential is discussed.