Forcing broken symmetry to recover static electronic correlation: the H2 molecule test case

Abstract

ABSTRACT A self-consistent field method based on a density matrix functional theory scheme is presented to compute the potential energy curve of the hydrogen molecule. A functional to recover the so-called cumulant correlation energy is introduced. The form of such functional is very simple being dependent explicitly only on the square of the overlap matrix element between the unrestricted non-orthogonal occupied orbitals of the calculation. The functional is a sum of two contributions referring to non-dynamic and dynamic correlation. The agreement with the full-CI potential energy curve is within chemical accuracy.