where Ψ gen int is a general interacting wavefunction, Ĥint is a general interacting Hamiltonian containing at most two-body operator terms, and Ψ gen 0 is a general noninteracting wavefunction. Note that the general Eq. 15 encompasses both DFT correlation energy expressions (Eqs. 7 and 9), as well as its MPAC/HF counterparts (Eqs. and).