It was well known (but mostly forgotten by many) that MP2 energy diverges for the electron gas. The same is probably true for the solids with small HOMO-LUMO gap. Even the presence of very diffuse orbitals in molecules often deteriorates MP2 energy. That is probably the reason of lack of MP2 calculations in solids. _______ Vitaly Rassolov rassolov %! at !% chem.nwu.edu Chemistry Department tel. (847) 491-3423 Northwestern University fax (847) 491-7713