Phase diagram of the TIP4P/Ice water model by enhanced sampling simulations

We studied the phase diagram for the TIP4P/Ice water model using enhanced sampling molecular dynamics simulations. Our approach is based on the calculation of ice-liquid free energy differences from biased coexistence simulations that reversibly sample the melting and growth of layers of ice. We computed a total of 19 melting points for five different ice polymorphs, which are in excellent agreement with the melting lines obtained from the integration of the Clausius-Clapeyron equation. For proton-ordered and fully proton-disordered ice phases, the results are in very good agreement with previous calculations based on thermodynamic integration. For the partially proton-disordered ice III, we find a large increase in stability that is in line with previous observations using direct coexistence simulations for the TIP4P/2005 model. This issue highlights the robustness of the approach employed here for ice polymorphs with diverse degrees of proton disorder. Our approach is general and can be applied to the calculation of other complex phase diagrams. Published under an exclusive license by AIP Publishing.

Automated summary

In this study, we utilized enhanced sampling molecular dynamics simulations to investigate the phase diagram of the TIP4P/Ice water model. By calculating the ice-liquid free energy differences, we obtained 19 melting points for five different ice polymorphs, which agreed well with theoretical calculations and experimental observations. This demonstrates the robustness of our approach for ice polymorphs with diverse degrees of proton disorder, and it can be applied to calculate other complex phase diagrams.