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 water (and heavy water), the simplest alcohols (MeOH and EtOH), and the simplest silica alkoxides (Si(OMe)4 and Si(OEt)4), at high pressures and temperatures and under ambient conditions. The same methodology is employed throughout to derive potentials for different species, and the same potentials are used for different thermodynamic conditions. The studies were carried out using two different MD codes, DISCOVER and DL_POLY, with slightly different implementations and force fields, to guarantee that the results would not be sensitive to details of the simulations. The results obtained with both codes for density, enthalpy of vaporization, and radial distribution functions compare very well with experiment, whereas the self-diffusion coefficients are slightly too high. The same general methodologies and sets of potentials should therefore be valid in describing complex liquids, such as silica-based sol−gel solutions, containing water, alcohol, and silica alkoxide, without having to redefine the force field on changing the composition or thermodynamic conditions.