On the dielectric theory and computer simulation of water

The static dielectric properties of ST2 water are carefully examined by means of a computer-adapted Kirkwood theory. “Experimental” data are provided by various molecular dynamics simulations involving 216. 500 and 1000 water molecules and corresponding to a variety of boundary conditions. It is shown that the integral of the respective modified T tensor plays the central role in matching different boundary conditions. Thus a unique dielectric constant σ = 82 ± 15 is obtained for a density p = 1 g/cm³ and a temperature T = 120°C. Furthermore, it is found that the constitutive relation P = [(σ - 1)/4 – is already fulfilled in a sample of a few hundred molecules. Finally, R-dependent Kirkwood g factors are discussed, which give a vivid picture, how different boundary conditions influence orientational correlations between water dipoles.