Multiconfiguration perturbation theory: size consistency at second order |
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Authors: | Szabados Agnes Rolik Zoltán Tóth Gábor Surján Péter R |
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Institution: | Department of Theoretical Chemistry, Loránd E?tv?s University, Budapest, Hungary. |
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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. |
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