Quantum Monte Carlo simulations of the structure in the liquid-vapor interface of BiGa binary alloys

Abstract

Abstract The liquid vapor interface of a pure metal has been the subject of a number of simulations by both molecular dynamics and Monte Carlo methods. In this work quantum :t\fonte Carlo calculations for an interface were carried out for electrons and ions in a self-consistent manner, making use of pseudopotentials for the ions, a jellium approximation to determine their densities, and a KohnSham treatment of the electrons. The quantum Monte Carlo aspect appears in the solution of Kohn-Sham equation, which is the same as the one-dimensional Schrodinger equation in this application, which relates the electron wavefunction 1/Jn to the position z normal to the surface and the effective electron potential Veir, which in turn depends on the electron density ne ( z). The solution of this equation for 1/Jn (z) and the energy En may be determined in variational QMC by the Metropolis sampling method. With ne(z) freshly determined and Veir revised, the process may be repeated, a new ne(z) determined, and so forth to achieve self-consistency. For a pure metal, the development of the ionic interactions and the pseudopotential is a rather complex procedure, and it is even more complex for the bismuth-gallium alloy described in this paper. The end results are structures of the interface expressed in terms of longitudinal distributions (normal to the surface) of each of the atomic species, a transverse pair distribution, and the electron densities. Experimental measurements of the structure of alloys such as these are available from grazing incidence x-ray studies. In this case, the measured and predicted longitudinal density profiles are in “rather good” agreement, but differ somewhat in the details.