Configuration interaction combined with spin-projection for strongly correlated molecular electronic structures

Abstract

We introduce single and double particle-hole excitations in the recently revived spin-projected Hartree-Fock. Our motivation is to treat static correlation with spin-projection and recover the residual correlation, mostly dynamic in nature, with simple configuration interaction (CI). To this end, we present the Wick theorem for nonorhtogonal determinants, which enables an efficient implementation in conjunction with the direct CI scheme. The proposed approach, termed ECISD, achieves a balanced treatment between dynamic and static correlations. To approximately account for the quadruple excitations, we also modify the well-known Davidson correction. We report our approaches yield surprisingly accurate potential curves for HF, H2O, N2, and a hydrogen lattice, compared to traditional single reference wave function methods at the same computational scaling as regular CI.

5 pages, 3 figures, 1 table, to appear in J. Chem. Phys

References in corpus (4)

• Solutions of the Two Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms
• Extended Møller-Plesset perturbation theory for dynamical and static correlations
• Configuration interaction combined with spin-projection for strongly correlated molecular electronic structures
• Angular Momentum Projected Configuration Interaction with Realistic Hamiltonians

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