Many-body effects on bandwidths in ionic, noble gas, and molecular solids

Electron bandwidths in LiD, LiF, LiCl, solid ${\mathrm{C}}_{60},$ MgO, KCl, Ar, and ${\mathrm{CaF}}_2,$ evaluated in the local-density approximation (LDA) and Hedin’s GW approximation, are noted. Bandwidths are underestimated by the LDA as compared to GW results or experiment. This is explained by exchange and correlation effects being strongest on atomic or molecular sites, which compresses bands, with the LDA overestimating such compression. It is reasonable for compression to occur because states at the band maxima have more nodes between atoms or molecules, so that they are more concentrated on such sites.