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((1)Σ(+)) 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 Re = 4.45a0. 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 J = 0 and J = 1 (total angular momentum).