Perturbative calculation of the Hartree-Fock interaction energy using orthogonalized orbitals

A many-body perturbation theory based on the partitioning of the dimer Hamiltonian, formulated in an orthogonalized basis set, is used for the calculation of interaction energies at the Hartree–Fock (HF) level. Numerical results for the (HF)2 and (H2O)2 systems in selected geometries are presented. The interaction-energy components are compared with the results obtained from the standard supermolecular approach and the intermolecular perturbation theory based on the biorthogonal basis set.