  Search for efficient materials for application in the fields of
optoelectronics and photovoltaics are active areas of research across the
world. The potential of compounds such as K${_3}$Cu${_3}$P${_2}$ is not yet
fully realized. Therefore, we perform the ab initio studies based on density
functional theory to investigate the structural, electronic, elastic, and
optical properties of K${_3}$Cu${_3}$P${_2}$. Ground state properties were
computed in three different scenarios, i.e: with spin-orbit coupling (SOC),
without spin-orbit coupling, and with Hubbard U parameter. Direct electronic
bandgaps of 1.338 eV, 1.323 eV and 1.673 eV were obtained for
K${_3}$Cu${_3}$P${_2}$ without SOC, K${_3}$Cu${_3}$P${_2}$ with SOC and
K${_3}$Cu${_3}$P${_2}$ with Hubbard U respectively. In all the cases, Cu-d
orbitals were dominant at the top of the valence band. The effect of SOC on the
K${_3}$Cu${_3}$P${_2}$ computed lattice constant and bandgap was insignificant.
The mechanical stability test indicated that K${_3}$Cu${_3}$P${_2}$ is
mechanically stable at zero pressure. The optical band gap was found to
increase by 0.635 eV when Hubbard U was taken into consideration. Generally,
the inclusion of the Hubbard U parameter in density functional theory improves
the predictions of the bandgap and optical properties.
