Sixth-order many-body perturbation theory for molecular calculations

By efficiently combining coupled-cluster iterations with the 2n + 1 rule of perturbation theory, we report full sixth-order MBPT. All terms are evaluated with a Hartree-Fock reference and the Mّller-Plesset separation of the Hamiltonian and less than an n9p rocedure. The total correction corresponds to 28300 antisymmetrized MBPT diagrams separated into 11 components. The approach is applied to several small molecules at various geometries to investigate the importance of the higher order corrections with respect to the quality of the reference function.