Determination of structural, electronic and optical properties of silicon, germanene and Si-Ge system by DFT

Abstract

In this study, the structural, electronic and optical properties of a set of bilayer sheets of silicon, germanium and the alloy of both were determined. The study is based on the theory of density functionals and its implementation in this work was carried out using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. A Perdew–Burke–Ernzerhof type generalized gradient pseudopotential (GGA-PBE) was used. In the first part of the study, the optimization of the test wave function and the K-point mesh was carried out by means of the Monkhorst-Pack algorithm in the first Brillouin zone, developing the structural optimization to determine the network parameters that minimize the energy of the system, obtaining for silicene the following network parameters a=b= 3.819 Å, and for germanene they were a=b= 4.035283 Å. In the second part of the study, the electronic behavior of the systems was established through their band structure and density of states, where conductive behavior was determined for all systems, joining the valence and conduction band at the point of high K symmetry. , showing the presence of Dirac cones. Finally, the imaginary part of the dielectric function was determined where absorption peaks are seen at different energy levels, associated with electronic phenomena in the system such as UV-visible absorption and transitions between bands.