Ab initio study of van der Waals and hydrogen-bonded molecular crystals with a periodic local-MP2 method

We have studied ab initio the cohesive energy of a set of six molecular crystals with CRYSCOR, a new program implementing a periodic local second-order Moller-Plesset perturbation theory (LMP2) method. The set of studied crystals includes hydrogen-bonded (ice XI, NH3, formic acid, HCN) and van der Waals (CO2, C2H2) crystals. A polarization-augmented triple-zeta quality basis set has been used throughout. The method allows us to obtain cohesive energies in good agreement with the experimental values. Results are also compared to those obtained with a recently proposed B3LYP augmented with an empirical dispersion term (D*) specifically tuned for bulk molecular crystals, and with those obtained through a spin component scaling of the LMP2 results. We finally analyze the correlation contribution to the cohesive energy by separating the intramolecular and intermolecular contribution, according to the distance between correlated electrons, allowing for an interesting insight on the role of weak interactions in the studied systems. In this respect, crystalline formic acid is analyzed in more detail. The investigation of the long range contribution to the cohesive energy also allows us to draw a correspondence between the ab initio LMP2 and empirical approaches used to describe dispersion interaction.