Formation and physical characteristics of van der Waals molecules, cations, and anions: Estimates of complete basis set values

Abstract

AbstractComplete basis set (CBS) values are sought either for highly accurate molecular characteristics of small species (e.g., pairs of rare gas atoms or the HF dimer) or for medium‐size molecules or ions (e.g., bases of nucleic acids, the benzene dimer). In the latter case, only the Møller–Plesset type 2 (MP2) procedure with DZ and TZ basis sets is feasible. In the present work, both aspects are relevant. Altogether 23 species and 7 reactions are treated, including van der Waals (vdW) molecules ((H2)2, rare gas dimers), cations (H … Rg, Rg = He, Ne, Ar, Kr), and anions associated with the CH potential energy surface (CH4 … H−, CH … H2, and the CH (D3h) Eyring activated complex). Use has been made of various extrapolation formulas. An exponential‐type formula is also reliable in instances when only small basis set data are available. By means of a formula used in our previous work (FX = F∞ + a n−1, where FX is a physical characteristics obtained with a cc‐pVXZ basis set and X is the cardinal number, F∞ a CBS value searched for, and n the total number of atomic functions in the basis set), it is possible to show that CBS ΔE values of association processes (e.g., A + B ⇋ A − B, where A and B are held together by a bond of variable strength) are essentially the same, regardless of whether simple or augmented basis sets are used when considering or neglecting corrections for the basis set superposition error (BSSE). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005