Influence of the Chalcogen Anion on the Structural, Electronic, Phonon, Thermal, and Optical Properties of Yttrium Hydride Chalcogenides Material YHX (X = S, Se, and Te): A First‐Principles Study

The structural, electronic, vibrational, optical, and thermodynamic properties of yttrium hydrogen chalcogenides (YHS, YHSe, and YHTe) are systematically investigated using first‐principles density functional theory (DFT), with phonon and thermodynamic properties determined using Phonopy calculations. All compounds are dynamically stable, exhibiting progressive lattice expansion from YHS to YHTe due to increasing chalcogen atomic size. Additionally chalcogen substitution effectively tunes the electronic structure by modulating the band gap and density of states (DOS) through enhanced hybridization between Y‐d and chalcogen‐p orbitals. Spin–orbit coupling (SOC) introduces subtle yet non‐negligible modifications, with stronger effects observed for heavier chalcogens Te‐based systems. The band gaps show slight SOC‐induced variations, changing from 1.6385 to 1.6472 eV for YHS, 1.5152 to 1.5172 eV for YHSe, and from 1.52 to 1.42 eV for YHTe, reflecting enhanced relativistic effects in Te‐based systems. YHS and YHSe retain indirect band gaps semiconductor, whereas YHTe exhibits a robust direct band gap semiconductor. Phonon dispersion confirms dynamical stability and reveals systematic softening of vibrational modes from YHS to YHTe, attributed to increased atomic mass and reduced interatomic force constants. This behavior correlates with enhanced electronic polarizability and modified bonding. Optical properties exhibit a red shift in the absorption edge with increased dielectric response. Thermodynamic analysis shows that entropy and specific heat increase with temperature, while Helmholtz free energy decreases and becomes more negative from YHS to YHTe, indicating improved thermodynamic stability. These findings highlight yttrium hydrogen chalcogenide compounds as promising tunable materials for optoelectronic and energy applications.