Correlated one-body potential from second-order Møller-Plesset perturbation theory: Alternative to orbital-optimized MP2 method

A mean-field (or one-particle) theory to represent electron correlation at the level of the second-order Møller-Plesset perturbation (MP2) theory is presented. Orbitals and associated energy levels are given as eigenfunctions and eigenvalues of the resulting one-body (or Fock-like) MP2 Hamiltonian, respectively. They are optimized in the presence of MP2-level correlation with the self-consistent field procedure and used to update the MP1 amplitudes including their denominators. Numerical performance is illustrated in molecular applications for computing reaction energies, applying Koopmans' theorem, and examining the effects of dynamic correlation on energy levels of metal complexes.