PNNL

Abstract

The details of the Graphical Processing Unit (GPU) implementation of the most compu- tationally intensive (T)-part of the recently introduced regularized CCSD(T) (Reg-CCSD(T)) method [K. Kowalski, M.Valiev 131, 234107 (2010)] for calculating electronic energies of strongly interacting systems are discussed. Parallel tests performed for several molecular systems show very good scalability of the triples part of the Reg-CCSD(T) approach. We also discuss the performance of the Reg-CCSD(T) GPU implementation as a function of the parameters defining the partitioning of the spinorbital domain (tiling structure). The accuracy of the Reg-CCSD(T) method is illustrated on two examples: the NiO2 molecule and open-shell Spiro cation (5,5’(4H,4H’)-spirobi[cyclopenta[c]pyrrole]2,2’,6,6’-tetrahydro cation), which is a frequently used model to study electron transfer processes. It is demonstrated that a simple regularization of the cluster amplitudes used in the non-iterative corrections accounting for the effect of triply excited configurations significantly improves the accuracies of groundstate energies in the presence of strong quasidegeneracy effects. For NiO2 we compare the Reg-CCSD(T) results with the CCSDT energies, whereas for Spiro cation we compare Reg-CCSD(T) results with the energies obtained with completely renormalized CCSD(T) method.