EXACT EXCHANGE POTENTIAL BAND-STRUCTURE CALCULATIONS FOR SIMPLE METALS - LI, NA, K, RB, AND CA

We present electronic band-structure calculations of simple metals (Li , Na, K, Rb, and Ca), where we use the exact Kohn-Sham density-functio nal exchange (EXX) potential combined with the LDA (local-density appr oximation) correlation potential. The method is the same as one exploi ted in the previous papers [Phys. Rev. B 50, 14816 (1994); Phys. Rev. Lett. 74, 2989 (1995)]. Surprisingly, in contrast to the case of semic onductors and insulators, the resulting eigenvalues of valence bands a re mostly in agreement with the corresponding LDA eigenvalues. In the case of Ca, where the empty d band exists above the Fermi energy, howe ver, the EXX calculation modifies the position of the d bands relative to the s bands considerably, implying the importance of treating the correlation energy on the same footing as the exchange energy.