Theoretical Studies of Potential Energy Surface and Bound States of the Strongly Bound He(¹S)–BeO (¹Σ⁺) Complex

We perform electronic structure calculations of the potential energy surface of the He···BeO­(¹Σ⁺) complex. We use several different methods to characterize this unusual interaction. We apply coupled cluster singles, doubles, and noniterative triples [CCSD­(T)] and the multireference configuration interaction [MRCI] levels of theory. The nature of the interaction is studied with symmetry-adapted perturbation theory (SAPT) based on DFT and CCSD description of the intramonomer electron densities. Our best estimate of the well depth is 1876.5 cm^–1 at the CCSD­(T) level, while the dissociation energy, corrected for the zero-point energy, is equal to 1446.7 cm^–1. The global minimum is located for the collinear He···Be–O geometry at <i>R</i>_e = 4.45<i>a</i>₀. The rotational constant of the He–BeO complex in its ground state is 0.863 cm^–1. We also calculate bound states of the He···BeO complex for <i>J</i> = 0 and <i>J</i> = 1 (total angular momentum)