Investigation of Optical and Electronic Properties of 2(,,) CuSbX X Se S Te Compounds in The Surface State at (001) Direction Using Density Functional Theory

In this paper, electronic and optical properties of chalchogenid 2( , , ) CuSbX X Se S Te  compounds have been studied in the surface state at (001) direction. Calculations done using pseudo-potential method within the framework of density functional theory (DFT) by using Quantum-Espresso software with the generalized gradient approximation (GGA). Band gap of 2( , ) CuSbX X Se S  in the bulk state is 0.81 and 0.93 eV respectively but in the surface state these compounds are no band gap, which the surface dangling bonds are covered the band gap. Calculations showed that the 2 CuSbTe in the bulk and surface states is metal. The surface energy, work function, density of states and optical properties in the surface state in the (001) direction are calculated with the three times of duplication layers and a 15 angstrom vacuum respectively. The experimental and theoretical results of these compound in the surface state are not available to comparison this calculation with them.