MONTE-CARLO SIMULATIONS OF WATER UNDER SUPERCRITICAL CONDITIONS .1. THERMODYNAMIC AND STRUCTURAL-PROPERTIES

The thermodynamic and structural properties of water along two supercritical isotherms at 673 and 773 K in the pressure range from 0.3 to 30 kbar have been studied by the NPT-ensemble Monte Carlo method using a TIP4P intermolecular pair potential. Simulated values of the configurational enthalpy, molar volume, isobaric heat capacity, isothermal compressibility, and thermal expansion coefficient are found to be in a rather good agreement with experimental data, although the critical point of the TIP4P water model is supposed to lie about 50 degrees lower than observed experimentally. The analysis of simulated atom-atom radial distribution functions as well as the dimerization energy distributions clearly shows that hydrogen bonding persists under the conditions studied, despite the fact that the water structure may be considered as "argon-like" in terms of oxygen-oxygen distribution functions (i.e. close to that of a simple liquid).