Unveiling the structural, Elastomechanical, and optoelectronic properties of HfHgX₂ (X = S, Se, Te) ternary...

The present study aims to theoretically explore the physical properties of HfHgX₂ (X = S, Se, Te) compounds. The structural, electronic, bonding, elastic, and optical properties are investigated using density functional theory based VASP code. Structural analysis unveils that HfHgX₂ (X = S, Se, Te) compounds crystallize in the trigonal crystal system with the R 3‾ m (No. 166) space group. The calculated structural and lattice parameters are in good agreement with the available literature data. The calculated formation energy values are -1.195622 eV (HfHgS₂), -1.257295 eV (HfHgSe₂), and -0.615084 eV (HfHgTe₂) showing the thermodynamic stability. The electronic properties reveal that HfHgS₂ possesses a direct band gap, whereas HfHgSe₂ and HfHgTe₂ exhibit indirect band gaps via PBE-GGA potential. The absence of imaginary phonons modes indicates the lattice dynamical stability of these studied compounds. The partial charge density distribution indicates that the occupied electronic states are predominantly localized around the chalcogen atoms, whereas the unoccupied electronic states are mainly localized around the Hf atoms providing the electronic transition route from X → Hf. The examination of -COHP demonstrates that Hf-X bonding interactions are the primary contributors to the structural stability of these compounds with ICOHP values for Hf-X (X = S, Se, Te) bonds are -3.107, -2.808, and -2.383 and corresponding ICOBI values of 0.644, 0.643, and 0.646 respectively. The direction-dependent optical properties were calculated along the ab-plane, c-axis, and total, revealing substantial directional dependence and pronounced optical anisotropy via PBE-GGA and SCAN potentials. The elastic properties confirm the mechanical stability criterion, indicating that the HfHgS₂ compound is less brittle than HfHgSe₂ and HfHgTe₂. The mechanical properties show that the HfHgX₂ (X = S, Se, Te) compounds are highly anisotropic due to their distinct bonding environment and the different interactions within the layers of their layered crystal framework.