Electronic and optical properties of ternary kagome Rb2Ni3S4: a density functional study

The application of semiconductors with optical properties has grown significantly in the development of semiconductor photovoltaics. Here, we explore the electronic and optical properties of ternary transition metal sulfide Rb$_{2}$Ni$_{3}$S$_4$ by means of density functional theory. From the structural perspective, Ni atoms are found to form a kagome-like lattice in a two-dimensional plane of Rb$_{2}$Ni$_{3}$S$_4$. From our calculations, Rb$_{2}$Ni$_{3}$S$_4$ is found to be a semiconductor with an indirect band gap of $\sim$0.67 eV. Strong hybridization was observed between the S-3\textit{p} with the Ni-3$d_{xz}$ and Ni-3$d_{yz}$ orbitals. Interestingly, a flat band was noticed below the Fermi level demonstrating one significant feature of kagome lattice. From the optical calculations, Rb$_{2}$Ni$_{3}$S$_4$ is found to exhibit optical activity in both the visible and lower ultraviolet regions of the incident photon energies. The optical response suggests this material may be a potential candidate for opto-electronic device, given its ability to interact with light across a broad range of wavelengths. This work is expected to motivate the experimental group for transport measurements and may provide a new foundation in optics.