Second virial coefficients of water beyond the conventional first-order quantum correction

We present high quality theoretical calculations for the second virial coefficient of water at low temperatures, beyond the conventional first order quantum correction (FOQC). The calculations were performed with some of the best ab initio potentials available at present in conjunction with an effective potential semiclassical approach that has proved to be of similar accuracy to converged path integral Monte Carlo. These new results are compared with FOQC and with some recent experimental correlations. Although a much better agreement with experiment is achieved, some differences still remain at very low temperatures. Possible reasons for these discrepancies are discussed.