CALCULATION OF THE DIELECTRIC FUNCTION OF LI METAL

The inverse microscopic dielectric function of Li metal is evaluated within the time dependent local density approximation (TLDA) using one-electron energies and wave-functions obtained by SCF band structure calculations. Even at larger values of transferred momentum the influence 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 change of the shape of the inverse dielectric function, Our theoretical results agree quite well with measurements of the dynamic structure function by use of inelastic X-ray scattering with transferred energy up to 18 eV. Unrealistic oscillations at still higher energies as well as the narrow width of the peaks indicate the limits of a one-particle scheme.