Orbital-invariant second-order many-body perturbation theory on parallel computers: An approach for large molecules

The equations for the second-order many-body perturbation theory [MBPT(2)] energy are derived in an orbital-invariant representation, analogous to that obtained with the method of self-consistent electron pairs of Meyer. This formulation is well suited to take advantage of the localized nature of interactions in large chemical systems in order to reduce the computational effort required to study them. This formulation of the MBPT(2) method also lends itself to implementation on parallel computers. We describe a scalable implementation in which the key data are distributed across the parallel computer rather than being replicated. Portability to both shared- and distributed-memory computer architectures is provided through the use of a subroutine library implementing a "global array" programming model. We demonstrate that this approach is scalable even for relatively small chemical systems.