  The electronic and the optical properties of metallic nitride (MN) monolayers
are studied using a DFT formalism. In most of these monolayers, the electron
density of the metallic atoms is much higher than that of the nitride atoms,
and ionic, covalent, and metallic bonds are found in M-N bonds, resulting in
fascinating electronic and optical properties. The optical band gap is varied
from almost $0.0$ to $3.0$~eV for the MN monolayers depending on the bond type
between the metallic and the nitride atoms, as well as the contribution of the
type of orbitals around the Fermi energy. The optical properties such as the
dielectric function, the excitation spectra, the refractive index, the
reflectivity, and the optical conductivity of MN monolayers are calculated. The
excitation energy and static dielectric constant are found to be inversely
proportional to the band gap at low photon energy. The MN monolayers with a
large band gap have good visible light functionality, while the MN monolayers
with a lower band gap are found to be active in the infrared region.
Furthermore, it is shown that the optical properties of MN monolayers show a
strong anisotropy with respect to the polarization of the incoming light.
Consequently, our results for the optical properties of MN monolayers show that
they could be beneficial in optoelectronic device applications.
