First Principle Investigation of Structural and Electronic Properties of monolayer Tungsten Disulfide (WS2 )

Abstract

In this thesis the first principle calculation of tungsten disulfide (WS2) is investigated with density functional theory (DFT) using Quantum Espresso package. Our study is based on Density Functional Theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, Vanderbilt (ultra soft) pseudopotentials and the plane wave basis set implemented in the Quantum-ESPRESSO package. The calculation of the total minimum energy and the total minimum force of WS2 is calculated as a function of cutoff energy and K-points sampling. The total minimum energy per cell is monotonically decreasing with increasing cutoff energy due to variational principle. However, this trend can not be predicted from increasing the k-points sampling. Moreover, the equilibrium lattice constant is calculated using results obtained from energy convergence test (i.e., 90 Ry and 7 × 7 × 1 ). The computational value of the equilibrium lattice constant is 3.23 ˚ A. This result is in good agreement with experimental value wich is 3.18 ˚ A . Finally, discussing band structure and density of state of two dimensional WS2, the electrical property of two dimensional WS2 is determined based on energy band gap.