Relativistic p-d gaps of 1T TiSe2, TiS2, ZrSe2and ZrS2

The relativistic corrections (RC) (spin-orbit, Darwin and mass-velocity) are calculated to the p-d gaps of 1T TiSe 2 , TiS 2 , ZrSe 2 and ZrS 2 using the self-consistent non-muffin-tin OPW band-structure results. RC are found to enlarge the p-d gaps. The corrected p-d gap of 1T TiSe 2 is estimated to be small and positive. RC to the p-d gap of the semiconductor ZrSe 2 improve agreement with the experimental gap. RC are found to be of secondary importance to the p-d gaps of the semiconductors TiS 2 and ZrS 2 .