Department of Chemistry and Biochemistry
University of Notre Dame
Notre Dame, Indiana 46556

The density maximum and temperature dependence of the self-diffusion constant were investigated for the soft sticky dipole (SSD) water model and two related re-parameterizations of this single-point model. A combination of microcanonical and isobaric-isothermal molecular dynamics simulations were used to calculate these properties, both with and without the use of reaction field to handle long-range electrostatics. The isobaric-isothermal (NPT) simulations of the melting of both ice-I_h and ice-I_c showed a density maximum near 260 K. In most cases, the use of the reaction field resulted in calculated densities which were were significantly lower than experimental densities. Analysis of self-diffusion constants shows that the original SSD model captures the transport properties of experimental water very well in both the normal and super-cooled liquid regimes. We also present our re-parameterized versions of SSD for use both with the reaction field or without any long-range electrostatic corrections. These are called the SSD/RF and SSD/E models respectively. These modified models were shown to maintain or improve upon the experimental agreement with the structural and transport properties that can be obtained with either the original SSD or the density corrected version of the original model (SSD1). Additionally, a novel low-density ice structure is presented which appears to be the most stable ice structure for the entire SSD family.