From Data Mining to First‐Principles Exploration of Structural Stability and Thermodynamic Properties of Co ₂ FeSi Heusler Compound

This work presents an integrated first‐principles investigation of the structural, mechanical, electronic, magnetic, and thermodynamic properties of the full‐Heusler compound Co ₂ FeSi using density functional theory within the Quantum ESPRESSO framework. The optimized lattice parameter and elastic constants agree well with available experimental and theoretical data, supporting the reliability of the adopted model. The calculated elastic constants satisfy the mechanical‐stability criteria and indicate ductile behavior, a relatively high bulk modulus, and marked elastic anisotropy. Spin‐polarized electronic‐structure calculations reveal pronounced exchange splitting and confirm ferromagnetism. However, finite electronic states remain at the Fermi level in both spin channels, indicating spin‐polarized metallic behavior rather than ideal half‐metallicity within PBE‐GGA. The total magnetic moment is approximately 5.37 μB per formula unit, mainly originating from the Fe and Co 3d states. Additional PBE‐GGA + U calculations, employing U _eff   =  4.8 eV for the Co‐3d orbitals and U _eff    =   4.5 eV for the Fe‐3d orbitals, increase the total magnetic moment to approximately 6.0 μB per formula unit. However, the Hubbard correction does not open a complete minority‐spin gap, and the compound remains spin‐polarized metallic under the present computational conditions. Thermodynamic properties, including Debye temperature, heat capacity, entropy, and free energy, were evaluated within the quasi‐harmonic approximation. The Debye temperature is about 486 K, and the thermodynamic functions exhibit the expected temperature dependence. Pressure‐dependent calculations further show increasing bulk modulus, model‐estimated hardness, and Debye temperature, providing a consistent description of Co ₂ FeSi under varying temperature and pressure conditions.