Solid–liquid phase diagram of the water octamer

By implementing the parallel-tempering algorithm to the isothermal–isobaric ensemble, the thermodynamic properties of (H2O)8 were determined. The constant pressure heat capacity, Cp, as a function of temperature at various pressures was computed in order to identify the cluster melting temperature. The temperature at which Cp reaches a maximum in the transition region was associated to the melting temperature of the cluster and used for the construction of the pressure–temperature phase diagram. The water octamer showed the usual solid–liquid transition with the melting temperature increasing as the pressure decreases, hence a negative slope in the solid–liquid line was obtained.