Characteristic curves of water: A force field assessment

The performance of popular water force fields under extreme conditions was studied using molecular simulations. Brown's characteristic curves were employed for the assessment. In total, 15 force fields were studied; all are rigid and non-polarizable. The characteristic curves enable an assessment of the force field over a wide range of states, including extreme conditions. Only fluid states were considered. Under moderate conditions, the IAPWS water equation of state was used as a reference. The comparison of the force fields yields important differences. All force fields yield the same topology for the characteristic curves, i.e., dome shaped in a double logarithmic pT diagram. Nevertheless, important quantitative differences for the performance of the different force fields are obtained. Overall, the TIP4P/2005 and SPC/E models give (among others) a reasonable description of the reference data. Furthermore, the computer experiments provide new insights into the topology of Brown's characteristic curves, which were originally postulated for simple fluids. Nevertheless, also for a strongly hydrogen bonding fluid such as water, no significant anomalies compared with simple fluids are observed.