THERMODYNAMICS OF SUPERCRITICAL AQUEOUS SYSTEMS

The MD simulations discussed in the following sections were performed using a conventional molecular dynamics algorithm for the canonical (NVE) ensemble and the flexible BJH water model (Bopp et al. 1983). The systems studied consisted of 200 H2O molecules in a cubic box with the side length adjusted to give the required density. The densities between 0.17 and 1.28 g/cm were chosen to correspond to the pressure range of 25 P 3000 MPa. 

Each simulation extended to about 15000 time-steps after a pre-equilibration of approximately the same length. Ewald summation in tabulated form was used for the Coulomb interactions, and the shifted-force method (e.g., Allen and Tildesley 1987) was used for the non-Coulomb parts of the BJH potential. All technical details of the simulations are described in detail elsewhere (Kalinichev and Heinzinger 1992, 1995 Kalinichev 1993). 

Macroscopic thermodynamic properties of simulated supercritical water 

With this correction, a very realistic representation of many thermodynamic properties of water over extremely wide ranges of temperature and density is observed in molecular computer simulations. This result gives us sufficient confidence in the following quantitative analysis and interpretation of the details of local geometric and energetic environments experienced by individual water molecules in terms of hydrogen bonding under supercritical conditions. 

Atomistic computer simulations are unique in providing a vast amount of detailed thermodynamic information on the properties, which are not readily measured in any experiment. One such property is the bonding energy  

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