  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.
