Pseudospectral Møller-Plesset perturbation theory through third order

We present a formulation and implementation of Møller-Plesset perturbation theory in a pseudospectral framework. At the second-order level, the pseudospectral formulation is a formally a factor of N/n faster than conventional approaches, while the third order is formally faster by a factor of n, where N is the number of atomic orbitals and n is the number of occupied orbitals. The accuracy of the resulting energies is probed for a number of test cases. Practical timings are presented and show conclusively that the pseudospectral formulation is faster than conventional ones.