CALCULATION OF THE DIELECTRIC FUNCTION OF LI METAL

The inverse microscopic dielectric function of Li metal is evaluated w ithin the time dependent local density approximation (TLDA) using one- electron energies and wave-functions obtained by SCF band structure ca lculations. Even at larger values of transferred momentum the influenc e of exchange and correlation is found to be quite small. Local fields are approximated by considering all elements of the dielectric matrix corresponding to the first and second shell of the reciprocal lattice vectors. Their influence is found to be orientation-dependent but in most cases quite small. However, in some cases they even cause a chang e of the shape of the inverse dielectric function, Our theoretical res ults agree quite well with measurements of the dynamic structure funct ion by use of inelastic X-ray scattering with transferred energy up to 18 eV. Unrealistic oscillations at still higher energies as well as t he narrow width of the peaks indicate the limits of a one-particle sch eme.