Structural, Electronic, Dynamic, and Optical Properties of 2D Monolayer Tungsten Telluride (2H-WTe2) under Small Biaxial Strain Using Density Functional Theory (DFT and DFT + U)

The structural, electronic, vibrational, and optical properties of 2D- 2H-WTe2 monolayer are investigated using density functional theory with respect to a plane wave ultrasoft pseudopotentials (PW-USPPs) in a generalized gradient approximation (GGA) and with the Hubbard potential (GGA + U). The equilibrium state properties such as lattice parameters, unit cell volume, bulk modulus, and its derivative are determined. The band gap values of monolayer 2H-WTe2 are investigated for unstrained, 2% biaxial compression, and biaxial tensile stress using GGA, respectively. The obtained band gap values of 2H-WTe2 with respect to GGA are 1.043, 1.1487, and 0.9439 eV for unstrained, biaxial compression, and tensile strain, respectively. Moreover, the band gap values determined using Hubbard correction (GGA + U) are 1.1089 eV (unstrained), 1.2332 eV (2% biaxial compression), and 0.9945 eV (2% biaxial tensile stress), respectively. The band gap value obtained using Hubbard correction predicts the experimental value more precisely. The projected density of state shows W (3d) orbital is more dominant both in the valence band maximum and conduction band minimum. Moreover, a small amount of tensile or compressive strain is used to tune the band gap of the monolayer without affecting its direct band gap nature. In addition to this, the phonon dispersion and optical properties are discussed for tensile strain, unstrained, and compressive strain, respectively.