Well-balanced basis sets for second-order Møller-Plesset treatment of argon-aromatic molecule complexes.

Efficient ab initio method for studies of van der Waals complexes of argon and aromatic molecules is presented. It is based on the supermolecular second-order Møller-Plesset (MP2) perturbation theory combined with well-balanced basis sets. The error resulting from incompleteness of such basis sets is almost exactly canceled by the correlation error inherent in the MP2 method. Two basis sets adapted to the MP2 method are selected from various medium-sized basis sets. The standard augmented correlation consistent polarized valence double-zeta basis set and a smaller reduced version derived from it are shown to perform exceptionally well. They are employed in a large scale computation of the potential energy surfaces of argon-benzene and argon-fluorobenzene complexes. The results are critically compared with ab initio high level coupled-cluster calculations and experimental data available. The calculated MP2 equilibrium geometry, dissociation energy, and the vibrational states of the stretching mode are proved to be in excellent agreement with the experiment. However, the bending fundamentals are systematically overestimated by about 1 cm(-1). This deficiency is removed by introducing a simple correction function which improves the MP2 potential energy surface. This function can be easily determined and applied to arbitrary argon-aromatic molecule complexes. The MP2 method is compared to the density-functional theory. Local, semilocal, and hybrid models are tested and the results obtained clearly show that none of these models is capable of accurate description of the van der Waals interaction.