Band structure and lattice instability of TiSe2

The energy band structure of TiSe2, determined in the local-density approach yields a semimetal (band overlap 0.20 0.05 eV) with holes at and electron pockets only at L. The dimensions of the electron pocket indicate the presence of (7-8) × 1020 carriers/cm3 in excellent agreement with both transport and angular-resolved photoemission data. The observed charge-density wave is attributed to characteristic "volume" effects, i.e., nesting of parallel electron-hole bands at EF separated by the -L zone-boundary wave vector.