Computational Investigation of Structural, Mechanical, Electronic, Thermodynamic, and Lattice Dynamical Properties of α-Phase LiGaSi₁₋ₓCₓ Alloys for Advanced Energy Applications

A comprehensive first-principles investigation has been conducted on the α-phase LiGaSi₁₋ₓCₓ alloy to explore its structural, mechanical, electronic, thermodynamic, and lattice dynamical properties. The study employs density functional theory (DFT) within the plane-wave pseudopotential method, using the alchemical mixing approximation as implemented in the ABINIT code. Ground-state properties, including lattice constants, bulk modulus, elastic constants (Cᵢⱼ), Young’s modulus (E), shear modulus (G), and energy gaps, were calculated for the parent compounds LiGaSi and LiGaC, showing strong agreement with previously reported theoretical results. For the LiGaSi₁₋ₓCₓ alloy, these properties are reported here for the first time, providing new insights into its compositional dependence and mechanical stability. Electronic structure analysis, performed using the Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange-correlation potential, reveals that the alloy exhibits an indirect bandgap (Γ to X) across all compositions, with the bandgap tunable from 0.59 eV to 1.51 eV depending on the carbon content. This tunability suggests promising potential for optoelectronic applications such as photosensors and light-emitting diodes (LEDs). Thermodynamic properties, including unit cell volume, bulk modulus, thermal expansion coefficient, heat capacity, and entropy, were examined as functions of temperature and carbon concentration. Phonon dispersion relations and phonon frequency analyses confirm the dynamical stability of the α-phase LiGaSi₁₋ₓCₓ alloy across the full compositional range studied.