Ab initio calculation of ε 2 ( ω ) including the electron-hole interaction: Application to GaN and CaF 2

We present a computationally efficient first-principles scheme to calculate e2(v) for crystalline insulators, including the electron-hole interaction. The effective Hamiltonian for electron-hole pairs contains both the exchange and direct parts of this interaction. An iterative scheme is used in which the v moments ofe2(v) are computed by repeated action of the Hamiltonian on electron-hole pair states. The scheme is applied to two insulators where there are significant experimental uncertainties in their ultraviolet optical properties: GaN and CaF2 . @S0163-1829 ~99!08507-0#