Density matrix and x-ray structure factors in LiH

Within the first-order density-matrix formalism of Löwdin, we show how to obtain the density matrix in closed-shell crystals setting up the inverse of the overlap matrix between Bloch sums at a few selected $\overrightarrow{\mathrm{k}}$ vectors. Overlap effects in x-ray structure factors in LiH are taken into account in the calculations avoiding to perform a spherical average of the charge density with regard to each nucleus. Using hydrogenic wave functions with optimized screening for LiH, we obtain structure amplitudes in better agreement with experiment than previous calculations.