title: A new size extensive multireference perturbation theory.
abstract: A new multireference perturbation series is derived based on the Rayleigh-Schrödinger perturbation theory. It is orbitally invariant. Its computational cost is comparable to the single reference Møller-Plesset perturbation theory. It is demonstrated numerically that the present multireference second- and third-order energies are size extensive by two types of supermolecules composed of H2 and BH monomers. Spectroscopic constants of F2(X1Σg+),Cl2(X1Σg+),C2-(X2Σg+),B2(X3Σg-),and C2+(X4Σg-) as well as the ground state energies of H2O, NH2, and CH2 at three bond lengths have been calculated with the second multireference perturbation theory. The dissociation behaviors of CH4 and HF have also been investigated. Comparisons with other approximate theoretical models as well as the experimental data have been carried out to show their relative performances.
authors.affiliation: Department of Chemistry and Chemical Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing, 100083, People's Republic of China; Beijing Key Laboratory for Science and Application of Functional Molecular and Crystalline Materials, Beijing, 100083, People's Republic of China.
authors.forename: Feiwu
authors.initials: F
authors.lastname: Chen
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Fan
keywords: Møller-Plesset perturbation theory; Rayleigh-Schrödinger perturbation theory; multireference perturbation theory; orbital invariance; single reference perturbation theory; size extensivity