The original derivation of the NEO-MP2 method was done by Swalina et al. ĥp (i 0 ) + ĝpp (i 0 ) + ĝep 0 (i 0 ) , (1) where N e is the number of electrons and N p the number of quantum mechanically treated nuclei, which are referred to by primed indices. The one-particle Hamiltonians for the respective system are denoted as ĥ and the two particle Coulomb-exchange operators are defined as ĝee (1)