MONTE-CARLO STUDY OF A SIMPLE-MODEL BULK-ICE-IH SYSTEM - P-T MELTING BEHAVIOR AT CONSTANT VOLUME

An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm3 consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when expansion occurs upon freezing) and gives an approximate value for the onset of constant-density "melting." In this simulation, the expected pressure slope reversal occurs near 280 K. Internal energy, specific heat, and two-dimensional structure factors for the constant-density H2O System are also monitored at 14 temperatures from 100 to 370 K and support the P-T analysis.