Molecular dynamics simulation of liquid H2O, MeOH, EtOH, Si(OMe)(4), and Si(OEt)(4), as a function of temperature and pressure

We use molecular dynamics simulations to model pure liquids, including wate r land heavy water), the simplest alcohols (MeOH and EtOH), and the simples t silica alkoxides (Si(OMe)(4) and Si(OEt)(4)), at high pressures and tempe ratures and under ambient conditions. The same methodology is employed thro ughout to derive potentials for different species, and the same potentials are used for different thermodynamic conditions. The studies were carried o ut using two different MD codes, DISCOVER-and DL_POLY, with slightly differ ent implementations and force fields, to guarantee that the results would n ot be sensitive to details of the simulations. The results obtained with bo th codes for density; enthalpy of vaporization, and radial distribution fun ctions compare very well with experiment, whereas the self-diffusion coeffi cients are slightly too high. The same general methodologies and sets of po tentials should therefore be valid in describing complex liquids, such as s ilica-based sol-gel solutions, containing water, alcohol, and silica alkoxi de, without having to redefine the force field on changing the composition or thermodynamic conditions.