Study of phase changes of the water octamer using parallel tempering and multihistogram methods

Parallel tempering Monte Carlo and multihistogram methods are combined to study the phase changes of the water octamer. The heat capacity is calculated continuously from very low temperatures up to T=230 K. We find the melting temperature to be 178.5 K. In addition, a solid-solid phase change is found at 12 K. We introduce an order parameter to monitor this low temperature phase change. (C) 2001 American Institute of Physics.