C Romero-Guzmán, J Algaba, C Vega, FJ Blas. J. Chem. Phys., 2026
https://doi.org/10.1063/5.0326799
The melting point of water is a fundamental thermodynamic property and a key benchmark for molecular simulations of phase behavior. Here, we estimate the melting temperature of the TIP4P/2005 and TIP4P/Ice models at ambient pressure using the direct coexistence method. We simulate systems containing up to 8640 water molecules and treat long-range interactions with the particle mesh Ewald approach for both electrostatics and dispersion [Lennard-Jones Particle-Mesh Ewald (LJ-PME)], thereby substantially reducing finite-size and cutoff-truncation artifacts. We find that, once these effects are properly accounted for, the melting point of both models increases by nearly 1 K relative to the values obtained from truncating the dispersion interactions at 8.5 Å. The resulting melting temperatures are 250.25 and 270.75 K for the TIP4P/2005 and TIP4P/Ice water models, respectively, thereby bringing the latter significantly closer to experiment. We also evaluate melting enthalpies at coexistence and find them largely insensitive to system size and the long-range treatment. Overall, these results highlight the importance of accurate long-range interactions in phase-coexistence simulations of water.