Wavevector dependent susceptibility nad dielectric function for copper

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Abstract
Calculations are reported of the wavevector dependent susceptibility chi (q) and dielectric function epsilon (q) for copper. Calculations have been performed using a simple band model consisting of a hybridized s-d band and a d sub-band. Since only these bands cross the Fermi level or lie close to it, they are expected to alone give dominant contributions to chi (q) and epsilon (q). The effects of including Umklapp processes are considered. The authors find that Umklapp processes can give rise to a small hump in chi (q) located q-(G-2kf) where G is a reciprocal lattice vector and Kf is the Fermi radius The matrix elements reduce chi (q) by a factor of two or three. The inclusion of matrix elements may introduce a slight structure. The effect of including electron-phonon interaction on chi (q) for copper is also studied.