DFT study of electronic and optical properties of silicene functionalized with chemical groups.

In the last years, a band-gap tunability is particularly interesting for the fabrication of flexible and ultrathin optical devices since it is known from earlier studies that two-dimensional materials can display a much larger sunlight absorption than commonly employed semiconductors. Using density functional theory, we study the structural, electronic and optical properties such as dielectric function, absorption coefficient, conductivity, and a refractive index of silicene monolayer functionalized with chemical groups or atoms (i.e, X-Si-Y, Cl-Si-Br, and X'-Si-X' with X = Cl, F, or OH; Y = CN; X'  = CN, CH, or NH). In this framework, by means of AIMD calculations, we show that they are dynamically stable, while their electronic band-gap, as obtained with the GGA approximation, ranges between 1.25 and 2.13 eV, except for CH-Si-CH and NH-Si-NH, which are found to be metallic. Additionally, we show that an external electric field can modify significantly the electronic structure of some of these systems.