Variational second-order Møller–Plesset theory based on the Luttinger–Ward functional

In recent years there have been some rather successful applications of a new variational technique for calculating the total energies of electronic systems. The new method is based on many-body perturbation theory and uses the one-electron Green function as the basic "variable" rather than the wave function of traditional variational calculations. It is the purpose of the present work to promote the new methods within the realm of traditional theoretical chemistry by demonstrating their utility for calculating the correlation energies of a number of atoms at a level corresponding to second-order Møller-Plesset perturbation theory. The generalization to any desired order of perturbation theory is not hard to accomplish.