Fluid density predictions using the COMPASS force field

Calculations of liquid densities for nine systems, each at two different state points, have been performed as specified for the First Industrial Fluid Properties Simulation Challenge. All calculations have utilized the current Version (2.6) of the COMPASS force field, with addition of recently refined parameters for alcohols, in conjunction with the Discover simulation program. Periodic cells containing 1000–2000 atoms have been subjected to 1.0 ns molecular dynamics simulation under conditions of constant temperature and pressure. Detailed analysis of the simulations has been performed to quantify uncertainties arising from both sampling statistics and other model and simulation protocol related errors. Accuracy of the predictions has been discussed separately for the aqueous and non-aqueous systems, with the former being found to give reliable predictions under ambient conditions but average to poor performance at higher temperatures and pressures. For non-aqueous systems other than 1,2,3-trichloropropane, a member of a group of compounds which have not been rigorously parameterized, density predictions are excellent and, significantly, are of comparable accuracy at both pairs of state points studied.