First-principles study of structural, electronic and vibrational properties of bulk and monolayer TiS2

In this paper the structural, electronic and vibrational properties of 3D bulk and 2D layer of TiS2 are studied. The PBE-GGA ansatz in the density functional theory together with the van der Waals interaction are considered deploying the plane wave pseudopotential method. The properties such as lattice parameters, elastic constants, bulk modulus, electronic band structure and the density of states of the ground state of hexagonal 3D bulk and 2D layered TiS2 are presented. The vibrational frequencies at the centre of the Brillouin zone are also reported. Effect of strain is seen on the electronic properties of the monolayers of TiS2. The results of the structural, electronic and vibrational properties are well in agreement with the available experimental results. The study finds that both bulk and monolayer TiS2 are semimetals with a small overlapping of bands near Fermi level. The band overlapping increases in the bulk TiS2 on applying pressure. The magnitude of phonon vibration frequencies increases with pressure. The monolayer TiS2 becomes metal when negative strain (compression) along xy plane is applied. On the contrary positive strain (tensile) opens an indirect bandgap in the monolayer TiS2.