Band structure and lattice instability of TiSe2

The energy band structure of Ti${\mathrm{Se}}_2$, determined in the local-density approach yields a semimetal (band overlap 0.20 ± 0.05 eV) with holes at $\Gamma$ and electron pockets only at $L$. The dimensions of the electron pocket indicate the presence of (7-8) × ${10}^{20}$ carriers/${\mathrm{cm}}^3$ 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 $E_F$ separated by the $\Gamma -L$ zone-boundary wave vector.