  Theoretically, NaAuS is predicted as topological insulator, while no detail
electronic structure study has been done for this compound. Here, we report the
structural and electronic properties of NaAuS by using LDA, PBEsol, PBE and
revPBE exchange correlation functionals. The calculated values of equilibrium
lattice constant for LDA, PBEsol, PBE and revPBE exchange correlation
functionals are found to be $\sim$6.128 {\AA}, $\sim$6.219 {\AA}, $\sim$6.353
{\AA} and $\sim$6.442 {\AA}, respectively. The bulk modulus predicted by LDA,
PBEsol, PBE and revPBE exchange correlation functionals is $\sim$66.6,
$\sim$56.4, $\sim$46.5 and $\sim$39.3 GPa, respectively. Hence, the order of
calculated values of bulk modulus is consistent with the order of calculated
values of equilibrium lattice parameters for these exchange correlation
functionals. The spread of total density of states below the Fermi level
decreases as the exchange correlation functional changes from LDA to PBEsol to
PBE to revPBE, which is also found to be consistent with the order of bulk
modulus for these exchange correlation functionals. In presence of spin-orbit
coupling, a direct band gap is observed in NaAuS compound, which is found to be
$\sim$0.26, $\sim$0.25, $\sim$0.24 and $\sim$0.23 eV for LDA, PBEsol, PBE and
revPBE exchange correlation functionals, respectively. Here, NaAuS is found to
be topological insulator as it shows band inversion at $\Gamma$ point. The
calculated values of band inversion strength for LDA (PBEsol) and PBE (revPBE)
exchange correlation functionals are $\sim$1.58 eV ($\sim$1.57 eV) and
$\sim$1.50 eV ($\sim$1.47 eV), respectively.
