We report the results of a Monte Carlo simulation for the structure of the stoichiometric CsAu melt, based on an ab initio quantum mechanical calculation of the interionic potentials, which is in excellent agreement with experiment,

The effects of three-body and, in a few cases, four-body and higher-order terms were studied for several Cu2+-(H2O)n (n up to 8) clusters proposed as models of the first hydration shell of the Cu2+ ion. This is based on ab initio SCF calculations performed for the n=6 cluster and for all the required tetramer, trimer and dimer subunits of this cluster and of the n = 8 cluster. The computed many-body results show that the three-body terms are non-negligible and lead to strong repulsive contributions to the total pairwise additive interaction energy of the Cu2+-(H2O)n systems. Pronounced changes on the hydration number (n) and on the optimal CuO distances (r) of this ion's first shell are obtained when two-body terms (n = 8, r = 2.09 Å)alone are considered or three-body terms (n = 6, r = 2.15 Å) are included. The four-body terms are found to be quite small in comparison with the three-body terms. The remaining higher-order terms are shown to be even much smaller than the four-body terms, thus indicating a rapid convergence of the many-body expansion of the interaction energy for this hydrated ion. This work suggests that, when a simple model is required for the interaction potential of metal ions with water, as it is the case in Monte Carlo or molecular dynamics simulations, a good degree of accuracy depends on supplementing the usual pairwise additive type of potential by three-body terms, and modelling of these depends on detailed studies of the type presented here. © 1990.