Exchange and correlation effects in the Visscher-Falicov model for metal intercalated graphite

Abstract

A simple model for metal intercalated graphite as a layered electron gas treated in the random phase approximation, which was proposed in early work of Visscher and Falicov, is extended to include exchange and short-range intraplane correlations between the electrons. Main attention is focussed on the static screening function of the model system, in relation to effective pair potentials in metal intercalants. The local field factor accounting for exchange and correlation is related to the intraplane electron structure factor and the latter is evaluated in a simple pseudoclassical approach, which is tested against known results for a quantal 2 D electron gas. Screening of an external point charge is shown to be appreciably modified by exchange and correlation in the case when it lies in an electron plane, leading to a deeper main attractive well between two external charges lying in the same electron plane. On the other hand, exchange and correlation have only minor effects when the charges lie at mid distance between two electron planes, at least if reasonable physical requirements are made on acceptable values for the electron screening length in the relevant range of model parameters.