title: Multiconfiguration perturbation theory: size consistency at second order.
abstract: A modified version of a previously elaborated multiconfiguration perturbation theory (MCPT) [Rolik et al. J. Chem. Phys. 119, 1922 (2003)] is presented. In the modified formulation size consistency is ensured at second order in energy, by omitting projectors from the zero order Hamiltonian operator. This MCPT formulation is abbreviated as SC2-MCPT (size consistent at second order). To ensure proper separability, we also require that energy denominators are constructed as differences of some one-particle energies. A similar choice for energy denominators also renders the well-known multireference Moller-Plesset (MRMP) energy size consistent at second order. The same thing applies to the related multireference perturbation theory by Witek, Nakano, and Hirao.
authors.affiliation: Department of Theoretical Chemistry, Loránd Eötvös University, Budapest, Hungary.
authors.forename: Agnes
authors.initials: A
authors.lastname: Szabados
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Rolik
authors.forename: Gábor
authors.initials: G
authors.lastname: Tóth
authors.forename: Péter R
authors.initials: PR
authors.lastname: Surján