The melting temperature of the six site model of Nada and van der Eerden (NvdE), is determined by using two different methods. A technique that is a combination of a Gibbs-Duhem integration and free energy calculations, can be used to refine the melting point of a potential. It also makes possible the determination of the coexistence point of a given model from the known value for a reference one. The melting temperature of NvdE potential was also calculated by direct coexistence. A set of N-p-T simulations was performed in which the solid and the liquid phases are put in contact. It was observed that the energy changes along the N-p-T simulation runs because, depending on the temperature of the system, the solid phase melts at the interface, and once phase change is completed, the energy remains constant.