Liquid Metal Free Energies from Ab Initio Potential Surfaces

For prediction of high pressure melting curves and liquid thermodynamic properties, it is desirable to evaluate liquid free energies. Direct free energy calculations from {\em ab initio} potential surfaces are very computationally intensive, especially for transition metals. Here we investigate Monte Carlo methods that involve sampling on the surface defined by a reference system. In principle, this allows for large gains in efficiency because the random walk is carried out on the (much faster) reference potential, and the {\em ab initio} potential is only evaluated on a small subset of uncorrelated configurations. We investigate the feasibility of these methods, and the role of the reference system. Results will be presented for liquid Mg and Ta.