A dynamical correlation model for variational two-electron reduced density matrix driven complete active space self-consistent field methods
Elvis Maradzike1 and A. Eugene DePrince III2
1,2Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390
We present a dynamical correlation model for the variational two-electron reduced density matrix- (v2RDM-) driven complete active space self consistent field (CASSCF) method. The model is based on Pernal’s adiabatic connection (AC) for CASSCF that relies upon transition density matrices derived from an extended random phase approximation (ERPA). The reduced density matrices (RDMs) that enter the ERPA and the AC can be obtained from v2RDMCASSCF. We validate the AC-v2RDM-CASSCF approach by computing potential energy curves for several small molecules. We explore the effects on the AC correlation energy of the N-representability of the RDMs from v2RDMCASSCF. We find that the AC-v2RDM-CASSCF approach recovers most of the dynamical correlation energy missing at the CASSCF level of theory, regardless of whether the RDMs satisfy only two-body or partial three-body N-representability conditions.