Monte Carlo Simulations of Water under Supercritical Conditions. II. Convergence Characteristics and the System Size Effects

The size dependence and convergence rates of thermodynamic averages during Monte Carlo simulations of supercritical water in a wide range of densities have been analysed and compared with simulations under normal conditions. It is shown that the fluctuations of internal energy (enthalpy) in NPT-ensemble Monte Carlo simulations of high-temperature water are strongly correlated with fluctuations of volume and the convergence of the thermodynamic averaging under such conditions depends on the frequency of volume-changing moves and may be considerably improved by increasing this frequency by a factor of 3 - 10 relative to generally accepted values