Global minima for water clusters (H2O)n, n ⩽ 21, described by a five-site empirical potential

Candidate global minimum structures are reported for (H2O)n clusters for n ⩽ 21 described by the rigid-body TIP5P potential. These structures are compared with previously published results for the related TIP4P potential, and with ab initio calculations at the MP2 level. The variation of the energy gap from the putative global minimum to the next-lowest structure as a function of system size is analysed. Comparisons with previously reported structural trends in water clusters are made.