ArC 2H 2: a challenging system for ab initio calculations

Abstract

The ArHCCH interaction is investigated by the supermolecular Møller-Plesset perturbation theory and coupled-cluster theory in conjunction with the perturbation theory of intermolecular forces. The interaction energy in this cluster is dissected into the fundamental components such as exchange, induction, and dispersion, and the anisotropy of the overall surface is analysed in terms of the angular behaviors of these components. The shape of the PES of ArHCCH is very sensitive to the level of ab initio theory. The coupled-cluster approach which included the single, double, and approximate triple excitations combined with the aug-cc-pvtz basis set supplemented by bond functions was necessary to obtain the best estimates of D e (within ± 5% error) for two minima: the global one for a skew T-configuration (118 cm −1), and a secondary one for the collinear arrangement (115 cm −1). The PES generated at a lower level of calculation was used in diffusion quantum Monte Carlo (DMC) calculations of the ground and first excited bending vibrational state of the cluster. The expectation values of the coordinates and rotational constants are provided for the ground state. DMC calculations are relatively unsensitive to the details of the PES. The nature and decomposition of three-body interactions in the related cluster Ar 2HCCH were also investigated.