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.