By implementing the parallel-tempering algorithm to the isothermal-isobaric ensemble, the thermodynamic properties of (H2O)(8) were determined. The constant pressure heat capacity. C-p, as a function of temperature at various pressures was computed in order to identify the cluster melting temperature. The temperature at which C-p 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. (C) 2002 Published by Elsevier Science B.V.