Structural and electronic properties of MX3 (M = Ti, Zr and Hf; X = S, Se, Te) from first principles calculations

The structural and electronic properties of layered TiS3, TiSe3, TiTe3, HfS3, HfSe3, HfTe3, ZrS3, ZrSe3 and ZrTe3 with structure P2(1)/m have been investigated using density functional theory for the first time at the atomic level within the vdW-DF and vdW-TS approximations to account for long range dispersive forces, which is important in predicting layered material interlayer spacing accurately. To get reasonable estimates of the band gaps, MBJ band structure calculations were performed. With exception of the tellurides and TiSe3, which are found to be metallic, the compounds are indirect band gap semiconductors with band gap in the range of 0.44 to 2.04 eV. The minimum direct band gaps were found to be in a similar range. The elastic constants of these structures confirm their mechanical stability by satisfying all the stability criteria for monoclinic structures. Phonon band structure and thermal properties were calculated using density functional perturbation theory. The phonon dispersion relations show that the structures are stable under small atomic displacements.