“…In general, however, comparisons have shown that there are systematic anisotropic discrepancies between theory and experiment. As already noted, momentum densities have been calculated using the QMC methods [26,27] and the GW approximation [9,10,25]. However, in the case of Si [26], and Li [27] (QMC) and Li [38,25] (GW ) the correlation correction is not found to differ appreciably from the LP corrected LDA results [31].…”