Improved minima-hopping. TIP4P water clusters, with

A novel combination of minima-hopping with translational and topology-modifying steps is used to locate putative global minima for TIP4P water clusters, ( H 2 O ) n . Our minima for n ⩽ 30 agree with previous results in all but two cases ( n = 28 , 29 ) for which we report lower-energy structures. New candidates are reported for the global minima of clusters with 31 ⩽ n ⩽ 37 . A clathrate-like structure with one water molecule in a cage first appears as the global minimum for n = 19 but the motif becomes persistent only for n > 24 . Global minimum structures with two internal molecules appear first for n = 26 and then for n > 30 .