Numerical Study on the Size Consistency of the Multireference Perturbation Theory

The size consistency of the multireference perturbation theory and multireference singly-excited and doubly-excited configuration interaction (MRSDCI) was investigated numerically with three super-molecular models composed of H2, He, and LiH monomers separated by a large distance. A small full configuration interaction was performed first over the model space and then multireference perturbation calculations were carried out. Numerical results demonstrated that the previously derived size consistent multireference second-order perturbation theory was size consistent with respect to the above three super-molecules. Its accuracy relative to the full configuration interacton (CI) was also discussed. Size consistent error of two sets of the multireference second-order and third-order perturbation theories as well as MRSDCI were studied and compared.