Electronic structure, optical properties and defect induced half-metallic ferromagnetism in kagome Cs2Ni3S4

Abstract Recent research focuses on electronic structure of kagome materials due to their fascinating properties such as topological insulators, Dirac semimetals, and topological superconductors. Materials with sizable electronic band gap are found to play vital role in device applications. Here, by means of density functional theory calculations, we study the electronic and optical properties of ternary transition metal sulphide Cs 2 Ni 3 S 4 by using the full potential local orbital code. Standard generalized gradient approximation (GGA) has been employed to consider the electron exchange and correlation effect, and modified Becke–Johnson (mBJ) potential has been used to obtain the accurate band gap of the material. From our electronic structure calculations Cs 2 Ni 3 S 4 is found to be nonmagnetic semiconductor with an indirect band gap of ∼1.4 eV within GGA + mBJ calculations. The structural analysis demonstrates that Ni atoms form a kagome lattice in a two-dimensional plane, resulting in the presence of a dispersionless flat band located below the Fermi energy. From the optical calculations, analyzing the dielectric function, loss function, and optical conductivity, Cs 2 Ni 3 S 4 is found to be optically active in the visible as well as lower ultraviolet energy ranges. This suggests that Cs 2 Ni 3 S 4 may be a suitable candidate for the opto-electronic devices. Additionally, this work may provides a foundation for the development of opto-electronic device and a framework for experimental work. We additionally investigated the effect of vacancy defects in Cs 2 Ni 3 S 4 to see it’s influence on the electronic and magnetic properties. Interestingly, the Cs-vacancy defect give rise to half-metallic ferromagnetism with an effective magnetic moment of 1 μ B per unit cell.