Benchmark Study of the Interaction Energy for an (H2O)16 Cluster: Quantum Monte Carlo and Complete Basis Set Limit MP2 Results

The quantum Monte Carlo method is used to calculate the binding energy of an (H2O)(16) cluster that has been the subject of several recent theoretical studies. The resulting interaction energy, -165.1(8) kcal/mol, is very close to our MP2 complete basis set limit interaction energy of -164.1 kcal/mol. Comparison of these results with those for the one-, two-, three-, and four-body interaction energies leads us to conclude that the five- and higher-body interactions are attractive, contributing over 2 kcal/mol to the net interaction energy of this (H2O)(16) isomer.