  In this work, we have studied the structural, elastic, mechanical,
electronic, bonding, acoustic, thermal and optical properties of TaX (X = P,
As) in detail via first-principles method using the density functional theory.
A comprehensive study of elastic constants and moduli shows that both TaP and
TaAs possesses low to medium level of elastic anisotropy (depending on the
measure), reasonably good machinability, mixed bonding characteristics with
ionic and covalent contributions, brittle nature and relatively high Vickers
hardness with a low Debye temperature and melting temperature. The minimum
thermal conductivities and anisotropies of TaX (X = P, As) are calculated. Bond
population analysis supports the bonding nature as predicted by the elastic
parameters. The bulk electronic band structure calculations reveal clear
semi-metallic features with signature Dirac cone-like dispersions near the
Fermi level. A pseudogap in the electronic energy density of states at the
Fermi level separating the bonding and the antibonding states indicates
significant electronic stability of tetragonal TaX (X = P, As). The
reflectivity spectra show almost non-selective behavior over a wide range of
photon energy encompassing visible to mid-ultraviolet regions. High
reflectivity over wide spectral range makes TaX suitable as reflecting coating.
TaX (X = P, As) are very efficient absorber of ultraviolet radiation. Both the
compounds are moderately optically anisotropic owing to the anisotropic nature
of the electronic band structure. The refractive indices are very high in the
infrared to visible range. All the energy dependent optical parameters show
metallic features and are in complete accord with the underlying bulk
electronic density of states calculations.
