The description of N2 and F2 potential energy surfaces using multireference coupled cluster theory

Abstract

The ground state potential energy surfaces (PES’s) for diatomic nitrogen and fluorine are examined using a version of our recently published linearized multireference coupled cluster method (MR-LCCM). Comparison calculations employing a variety of standard ab initio techniques such as single reference configuration interaction singles and doubles (CISD), many-body perturbation theory (MBPT), coupled cluster single and doubles (CCSD), and multireference (MR)-CISD were also performed. In addition, the PES’s were also investigated using the newly developed CCSDT-1 method, which includes the dominant effect of T̂3. These single reference procedures fail in various ways (with the possible exception of the CCSDT-1 method), while the MR-LCCM method is shown to compare favorably to the more traditional MR-CI techniques. Like the MR-CIs, the MR-LCCM energy curves dissociate correctly and the two are nearly parallel.