Ab initio calculations of the electronic and optical properties of 1T-HfX2 compounds

The electronic and optical properties of the 1T-HfX2 (X=S, Se and Te) compounds have been studied using the full potential linear augmented plane wave (FPLAPW) method within the local density formalism. Our calculations show that 1T-HfS2 and 1T-HfSe2 are semiconductors with indirect Kohn–Sham gaps of 0.62 and 0.55 eV, respectively, while 1T-HfTe2 is metallic having density of states at Fermi energy around 0.9 states/eV unit cell. Our calculations suggest that the trends in the band structures of the 1T-HfX2 series can be attributed to both the atomic species and structural parameters. Replacing S by Se and Te causes to separate the Hf–f states from the chalcogen–s states and the Hf–d states. The frequency dependent dielectric function, reflectivity and absorption coefficient show considerable anisotropy at low energies. We present a detailed comparison with the available experimental data and find good agreement.