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We present calculations of the free energy, and hence the melting properties,of a simple tight-binding model for transition metals in the region of d-bandfilling near the middle of a d-series, the parameters of the model beingdesigned to mimic molybdenum. The melting properties are calculated forpressures ranging from ambient to several Mbar. The model is intended to be thesimplest possible tight-binding representation of the two basic parts of theenergy: first, the pairwise repulsion due to Fermi exclusion; and second, thed-band bonding energy described in terms of an electronic density of statesthat depends on structure. In addition to the number of d-electrons, the modelcontains four parameters, which are adjusted to fit the pressure dependentd-band width and the zero-temperature pressure-volume relation of Mo. We showthat the resulting model reproduces well the phonon dispersion relations of Moin the body-centred-cubic structure, as well as the radial distributionfunction of the high-temperature solid and liquid given by earlierfirst-principles simulations. Our free-energy calculations start from the freeenergy of the liquid and solid phases of the purely repulsive pair-potentialmodel, without d-band bonding. The free energy of the full tight-binding modelis obtained from this by thermodynamic integration. The resulting meltingproperties of the model are quite close to those given by earlierfirst-principles work on Mo. An interpretation of these melting properties isprovided by showing how they are related to those of the purely repulsivemodel.

Melting properties of a simple tight-binding model of transition metals: I.The region of half-filled d-band