Molecular dynamics simulations of rigid and flexible water models: Temperature dependence of viscosity

Abstract

Molecular dynamics (MD) simulations are carried out on a system of rigid or flexible water molecules at a series of temperatures between 273 and 368 K. Collective transport coefficients, such as shear and bulk viscosities are calculated, and their behavior is systematically investigated as a function of flexibility and temperature. It is found that by including the intramolecular terms in the potential the calculated viscosity values are in overall much better agreement, compared to earlier and recent available experimental data, than those obtained with the rigid SPC/E model. The effect of the intramolecular degrees of freedom on transport properties of liquid water is analyzed and the incorporation of polarizability is discussed for further improvements. To our knowledge the present study constitutes the first compendium of results on viscosities for pure liquid water, including flexible models, that has been assembled.