Polarizable point-charge model for water: Results under normal and extreme conditions

Molecular dynamics simulations of liquid water under normal and extreme conditions are performed using the polarizable point-charge (PPC) model. This efficient three-site model explicitly incorporates results from ab initio studies of the water molecule in applied electric fields. The structural, thermodynamic, and dielectric properties, and the self-diffusion coefficient are examined at a number of temperatures ranging from 263 to 573 K. These simulation results are compared with available experimental data along the liquid-vapor coexistence line; the agreement is very good for all properties studied. The temperature of maximum density for the PPC model is found to coincide with the experimentally observed value of 277 K. The spatial coordination of water molecules in the liquid and the anisotropy of the self-diffusion tensor are analyzed at various state points. Increased directional anisotropy in the local translational diffusion, suggestive of prenucleation phenomena, can be observed at T=263 K. Above T=473 K the local translational anisotropy becomes rather insensitive to temperature variation indicating a weakening of the correlations between water molecules. Rototranslational dynamics and nonlinear polarization effects arising in polarizable models for water are discussed along with their phenomenological implications. The dimer properties for the PPC potential are also reported. (C) 1996 American Institute of Physics.