In Møller-Plesset perturbation theory, the dynamic correlation energy is estimated as a series of perturbative terms originating from Rayleigh-Schrödinger perturbation theory around a zero order Hamiltonian given by the sum of Fock operators . By taking the ground state Slater determinant that solves the Hartree-Fock problem as the unperturbed wave function, the total electronic energy E is approximated at second order by the sum of the Hartree-Fock (HF) energy and the second-order Møller-Plesset (MP2c) correlation contribution,