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 u niversal local electron-ion pseudopotential of Nogueira, Fiolhais, and Perd ew [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 liqu id-vapor interface of Ga predicted by self-consistent quantum Monte Carlo s imulations with the observed structure. We find that the structure of the b ulk 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 parti cular, the longitudinal density distribution in the liquid-vapor interface predicted using the universal local pseudopotential is stratified, with a s pacing of about one atomic diameter and a decay length of a few atomic diam eters, 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 di stributions 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 inter face structures of Ga and Hg. The results obtained imply that the nonlocali ty of the pseudopotential is critical to a correct description of the struc ture of an inhomogeneous metal.