A natural orbital diagnostic for multiconfigurational character in correlated wave functions

Gordon MS; Schmidt MW; Chaban GM; Glaesemann KR; Stevens WJ; Gonzalez C

Journal of Chemical Physics, Vol.110, No.9, 4199-4207, 1999

Gordon MS, Schmidt MW, Chaban GM, Glaesemann KR, Stevens WJ, Gonzalez C

The natural orbitals and their corresponding occupation numbers are constructed for several interesting problems to demonstrate that the existence of negative natural orbital occupation numbers for single reference correlation methods provides a simple diagnostic for the need for a multiconfigurational description of the wave function.

Keywords:2ND-ORDER PERTURBATION-THEORY;ONE-ELECTRON PROPERTIES;COUPLED-CLUSTER THEORY;LEVEL SHIFT;BASIS SETS;OPEN-SHELL;SPECTROSCOPY;MOLECULES;ENERGY