A Monte Carlo study of structural and thermodynamic properties of water: dependence on the system size and on the boundary conditions

The structural and thermodynamic properties of water are studied using the force bias Monte Carlo simulation. In particular for ST2 water, the effect of system size is examined with 27, 125 and 216 water molecules. The role played by the truncation of the intermolecular potential is analysed using two different truncations, the spherical cut-off and the cubic cut-off. Also a recent simulation with the Watts potential using Ewald summation by McDonald and Klein is compared with one employing the spherical cut-off. In all cases the angular correlation functions show a strong dependence on the type of boundary condition used, whereas the usual radial functions g oo(r), g oh(r) and g hh(r) do not depend much on the boundary conditions. Because of this dependence of angular correlations on the boundary conditions, care must be exercised in comparing simulation results from small systems to real experiments.