Fast local-MP2 method with density-fitting for crystals. II. Test calculations and application to the carbon dioxide crystal

摘要

A density fitting scheme for calculating electron repulsion integrals used in local second order M0ller-Plesset perturbation theory for periodic systems (DFP) is presented. Reciprocal space techniques are systematically adopted, for which the use of Poisson fitting functions turned out to be instrumental. The role of the various parameters (truncation thresholds, density of the k net, Coulomb versus overlap metric, etc.) on computational times and accuracy is explored, using as test cases primitive-cell- and conventional-cell-diamond, proton-ordered ice, crystalline carbon dioxide, and a three-layer slab of magnesium oxide. Timings and results obtained when the electron repulsion integrals are calculated without invoking the DFP approximation, are taken as the reference. It is shown that our DFP scheme is both accurate and very efficient once properly calibrated. The lattice constant and cohesion energy of the CO_2 crystal are computed to illustrate the capabilities of providing a physically correct description also for weakly bound crystals, in strong contrast to present density functional approaches.