  We present first-principles density functional theory (DFT) investigations of
mechanical, thermodynamic and optical properties of synthesized
inverse-perovskites Sc3InX (X = B, C, N). The elastic constants at zero
pressure and temperature are calculated and the anisotropic behavior of the
compounds is illustrated. All the three materials are shown to be brittle in
nature. The computed Peierls stress, approximately 3 to 5 times larger than of
a selection of MAX phases, show that dislocation movement may follow but with
much reduced occurrences compared to these MAX phases. The Mulliken bonding
population and charge density maps show stronger covalency between Sc and X
atoms compared with Sc-Sc bond. The Vickers hardness values of Sc3InX are
predicted to be between 3.03 and 3.88 GPa. The Fermi surfaces of Sc3InX contain
both hole- and electron-like topology which changes as one replaces B with C or
N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye
temperature are calculated as a function both temperature and pressure using
the quasi-harmonic Debye model with phononic effects. The results so obtained
are analysed in comparison to the characteristics of other related compounds.
Moreover optical functions are calculated and discussed for the first time. The
reflectivity is found to be high in the IR-UV regions up to ~ 10.7 eV (Sc3InB,
Sc3InC) and 12.3 eV (Sc3InN), thus showing promise as good coating materials.
  Keywords: Sc3InX, Mechanical properties; Fermi surface; Quasi-harmonic Debye
model; Thermodynamic properties; Optical properties
