First-principles study of shear deformation on Mg adsorption by monolayer SnS 2

Abstract

Abstract Context In this study, the effects of different shear deformations on the structural stability, electronic structure, and optical properties of the Mg atom adsorption system of S vacancy defect SnS2 are systematically investigated based on density functional theory. It is shown that the presence of S-vacancy defects makes the band gap value of the system significantly smaller than that of a perfect SnS2 monolayer, and the SnS2 system changes from a direct band gap semiconductor to an indirect band gap semiconductor. The optimal adsorption position of Mg atoms in the S-vacancy defects SnS2 system is above the S atom when the adsorption energy is the largest and the system is the most stable. The density of states of the adsorption system is predominantly contributed by the S-3p and Sn-5s orbital electrons. The imposition of shear deformation leads to the introduction of certain impurity energy levels in the adsorption system, and the gap in the density of states near the Fermi energy level decreases. The charge transfer indicates that 0.96e of electrons are transferred from Mg atoms to S atoms at the surface of the adsorption system. The absorption and reflection peaks of the S-vacancy SnS2 adsorption system with Mg atoms were red-shifted and appeared in the ultraviolet region as compared to the intrinsic SnS2. This improves the utilization of the adsorption system for ultraviolet light to a great extent. Methods The model calculations in this paper are performed using the CASTEP module of the Material Studio (MS) software based on the first principles of Density Functional Theory (DFT) [21] for plane wave artifacts. Geometrical optimization and computational procedures are used to calculate the exchange correlation energy using the Perdew-Burke-Ernzerhof (PBE) generalized function [22] of the Generalized gradient approximation (GGA). The Monkhorst-Pack method [23] was used to rationalize the sampling of the highly symmetric k-points in the Brillouin zone. The grid of k-points is set to be 6 × 6 × 1. The plane-wave truncation energy is set to be 400 eV. The energy convergence criterion is 1.0 × 10− 5 eV. The residual stress of all atoms is 0.01 eV/Å. A vacuum layer with a thickness of 15 Å is set up in the z-direction, which ensures that the interactions of the system along the z-axis between the top and the bottom layers can be ignored during the whole simulation process.A 3 × 3 × 1 single-layer of SnS2 containing 27 atoms is used as a model for the calculations. The intrinsic SnS2 contains 9 Sn atoms and 18 S atoms.