Parallel-tempering Monte Carlo simulations of the finite temperature behavior of (H2O)6−

The parallel-tempering Monte Carlo method is used in combination with a Drude model to characterize the (H2O)6− cluster over the 50–190 K temperature range. Chainlike structures are found to account for about 50% of the population at 190 K, whereas they are unimportant at the temperatures below about 130 K. At the lowest temperature considered, prismlike structures are dominant. Two new low-energy forms of (H2O)6− are identified.