Test of the universal local pseudopotential for the description of an inhomogeneous metal

We present the results of a test of the adequacy of the recently proposed universal local electron-ion pseudopotential of Nogueira, Fiolhais, and Perdew [Phys. Rev. B 59, 2570 (1999)] for the prediction of the structure of an inhomogeneous metal. The test is a comparison of the structure of the liquid-vapor interface of Ga predicted by self-consistent quantum Monte Carlo simulations with the observed structure. We find that the structure of the bulk liquid metal predicted using the universal local pseudopotential is in good agreement with experimental data if an effective temperature replaces the true temperature. However, the predicted structure of the Liquid-vapor interface is only in qualitative agreement with experimental data. in particular, the longitudinal density distribution in the liquid-vapor interface predicted using the universal local pseudopotential is stratified, with a spacing of about one atomic diameter and a decay length of a few atomic diameters, features all of which are in qualitative agreement with observations. However, the amplitude of the predicted density oscillations is fivefold too large. Similar discrepancies are found when the longitudinal density distributions in the liquid-vapor interfaces of Sn and Pb predicted using the universal local pseudopotential are compared with those predicted using a nonlocal pseudopotential known to predict accurately the liquid-vapor interface structures of Ga and Hg. The results obtained imply that the nonlocality of the pseudopotential is critical to a correct description of the structure of an inhomogeneous metal.