Comparison of Theoretical and Experimental Charge Densities for C, Si, Ge, and ZnSe

Fourier transforms of the charge densities of C (diamond), Si, Ge, and ZnSe are calculated using the self-consistent orthogonalized-plane-wave (OPW) programs developed at the Aerospace Research Laboratory. Results obtained with the Slater, Kohn-Sham, and Liberman exchange approximations are compared with the most reliable experimental results and with previous theoretical results (obtained for diamond only). While the results are better than the free-atom form factors, there are still significant discrepancies between theoretical and experimental values.