Water clusters (H2O)n, n=6-8, in external electric fields.

Structural evolution of water clusters, (H2O)n, n=6-8, induced by a uniform static external electric field is studied within the density functional theory. The electric field is seen to stretch the intermolecular hydrogen bonds in the water clusters, eventually breaking them at some characteristic threshold value, triggering a conformational transformation to a lower energy. The transformed configurations appear as local minima on the cluster's multidimensional potential energy landscape with the applied field as an extra coordinate. This transformation is accompanied by a rather abrupt increase in the electric dipole moment over and above its steady, albeit nonlinear increase with the applied field. The overall effect of the applied field is the "opening up" of three dimensional morphologies of water clusters to form linear, branched, or netlike structures by making the dipolar water monomers align along the field axis. Consequently, the number of hydrogen bonds in a cluster decreases, in general, with an increase in the field strength. It has been observed that moderately low fields (Field strength<or=0.008 a.u.) markedly alter the ordering of the lowest energy configurations.