Theoretical Investigation of the Structural Stability and Optoelectronic Properties of La ₂ HfSe ₅

ABSTRACT

Rare‐earth transition‐metal chalcogenides remain largely unexplored despite their potential for functional applications. In this work, we present the first comprehensive first‐principles investigation of the structural, mechanical, vibrational, thermodynamic, electronic, and optical properties of orthorhombic . Structural optimization confirms the stability of the Pnma phase characterized by robust Hf–Se polyhedral bonding. The calculated elastic constants satisfy the Born mechanical stability criteria, while the Pugh ratio (1.96) and Poisson's ratio (0.28) indicate ductile behavior with moderate stiffness. Phonon dispersion calculations reveal the absence of imaginary frequencies, confirming dynamical stability, and yield a Debye temperature of 262 K. Electronic structure calculations identify as a direct band gap semiconductor with band gaps of 0.67 eV (GGA) and 1.36 eV (HSE06). The density of states indicates dominant Se‐p states in the valence band and La/Hf‐d states in the conduction band. Optical analysis reveals strong visible‐range absorption with coefficients on the order of 10 and an optical band gap of 1.58 eV. These results establish as a previously unexplored, mechanically stable, and optically active semiconductor, highlighting its potential for optoelectronic and energy‐conversion applications.