The effect of bond functions on intermolecular interactions for van der Waals dimers of neon, methane, and perfluoromethane

We present a comprehensive study of intermolecular interactions in van der Waals complexes including the dimers Ne2, (CH4)2, (CF4)2, CF4-CH4, CH4-Ne, and CF4-Ne, within the framework of second-order Møller-Plesset perturbation theory (MP2). This methodology was employed to compute and analyze the behavior of the reduced two-particle reduced density matrix (2RDM) and related two-particle density. It was shown that the region near the minimum of the correlation component of the 2RDM associated mainly with the Coulomb hole significantly affects the dispersion interaction energies of the systems concerned. As one of the consequences, the bond function approach to deal with the intermolecular correlation energies calculations was found to essentially and consistently enhance the convergence of the results with respect to the basis set size if the auxiliary functions were placed to cover the 2D minimum region. For asymmetric dimers, this general finding was further validated through a series of CCSD(T) calculations of the correlation energies.