Investigation of LiScNiSi Heusler alloy's physical characteristics under pressure: Use in optoelectronics with the HSE06 hybrid function

In this study, we used density functional theory $\left(\text{DFT}\right)$ to analyze the behavior of the unique Heusler-type quaternary compound LiScNiSi at ambient pressure and at pressures ranging from $0\text{to}100\text{GPa}$. The investigation covers the material's mechanical, electronic, optical, and structural properties. $\text{LiScNiSi}$ has been shown to exhibit semiconducting behavior, characterized by an indirect bandgap that increases under applied pressure in the range of 0 to $100\text{GPa}$. Specifically, the bandgap expands from 0.712 eV to 1.466 eV according to calculations performed using the Generalized Gradient Approximation (GGA), and from 1.766 eV to 2.036 eV when using the HSE06 hybrid functional.

For the valence and conduction bands, calculation of the density of states (DOS) shows that they are mainly made up of Sc and Ni d-orbitals. Increased pressure leads to a reduction in the lattice parameter, from $5.979\AA$ to $5.241\AA$, which significantly affects the material's strength and flexibility. Calculations of mechanical properties confirm this hypothesis, showing that the material retains its mechanical stability over the entire range of applied pressures, and adopts a ductile behavior from $40\text{GPa}$ upwards, in line with Pugh's criterion (B/G > 1.75). Indeed, the B/G ratio varies from 1.755 to 2.081 when the pressure is increased from 40 to $100\text{GPa.}$

The dynamic stability of the material in the pressure range studied was also confirmed by the study of phonon dispersion spectra at $0\text{GPa}\text{and}100\text{GPa}$, as all frequencies were found to be positive. Research into the material's optical properties reveals that it has a high refractive index, substantial optical conductivity, and excellent absorption and reflectivity. This makes LiScNiSi a prime option for applications involving protection from ultraviolet radiation.