Global potential energy minima of SPC/E water clusters without and with induced polarization using a genetic algorithm

The global minimum potential energy structures of water clusters, (H2O)(n), n = 2-14, have been calculated for the SPC/E (Simple Point Charge/Extended) model and a recent fluctuating charge version of the latter using a simple genetic algorithm. The SPC/E cluster geometries are in good agreement with previous TIP3P (Transferable Intermolecular Potential-3 Point) and TIP4P (Transferable Intermolecular Potential-4 Point) calculations as well as the interpretation of experimental measurements. In contrast to this, the polarizable version of the SPC/E model, which is based on the fluctuating charge approach, deviates rather strongly for n = 6 with few exceptions. However, comparing the polarizable model to ab initio results for identical cluster geometries we find reasonable agreement for the magnitude of the average molecular dipole moment, the corresponding energy per molecule, and the average oxygen-oxygen distance as functions of n.