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J Chem Phys. 2008 Apr 21;128(15):154103. doi: 10.1063/1.2889388.

Explicitly correlated RMP2 for high-spin open-shell reference states.

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  • 1Institut für Theoretische Chemie, Universität Stuttgart, Stuttgart, Germany.

Abstract

We present an explicitly correlated version of the high-spin open-shell RMP2 method. The theory is derived in a unitarily invariant form, which is suitable for the insertion of local approximations. It is demonstrated that the rapid basis set convergence of closed-shell MP2-F12 is also achieved in RMP2-F12, and similar Ansatze and approximations can be employed. All integrals are computed using efficient density fitting approximations, and many-electron integrals are avoided using resolution of the identity approximations. The performance of the method is demonstrated by benchmark calculations on a large set of ionization potentials, electron affinities and atomization energies. Using triple-zeta basis sets RMP2-F12 yields results that are closer to the basis set limit than standard RMP2 with augmented quintuple-zeta basis sets for all properties. Different variants of perturbative corrections for the open-shell Hartree-Fock treatment are described and tested.

PMID:
18433186
[PubMed]
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