New basis sets for the evaluation of interaction energies: an ab initio study of the He–He, Ne–Ne, Ar–Ar, He–Ne, He–Ar and Ne–Ar van der Waals complex internuclear potentials and ro-vibrational spectra

Abstract

We investigated the performance of medium-size basis sets in calculations of interaction energies for small van der Waals complexes. After careful numerical tests we derived new efficient basis sets (modified LPol-n bases, MLPol-n) for the evaluation of the interaction energies for He–He, Ne–Ne, Ar–Ar, He–Ne, He–Ar and Ne–Ar complexes. Additionally, we carried out systematic basis set studies taking as a starting point Jensen's aug-pc-2 basis set. In both cases we considered the addition of midbond functions to the bases. The proposed MLPol-n sets use the model of a harmonic oscillator embedded in an external electric field and belong to the family of Pol bases. The quality of the MLPol-n sets was first tested through finite-field Hartree–Fock atomic polarizability calculations. Next we obtained coupled cluster singles and doubles (CCSD), including connected triples, CCSD(T), interaction potentials for the six van der Waals complexes, and taking as reference the most accurate theoretical values available in the literature, we implemented new basis sets for the evaluation of the interaction energies. To test the potentials further we used them to calculate the ro-vibrational spectra for the complexes. The results are in very good agreement with the experimental data. In the future, we plan to extend the study to larger van der Waals complexes.