Investigation of optoelectronic and thermoelectric properties of Cu ₂ MSnX ₄ (M = Mg, Cd, Hg; X = S, Se) compounds

In this work, the structural, elastic, electronic, optical, and thermoelectric properties of Cu2MSnX4(M = Mg, Cd, Hg; X = S, Se) compounds were systematically investigated using first-principles calculations within the FP-LAPW framework of density functional theory (DFT). Structural optimisation revealed that the stannite and kesterite configurations are energetically favourable depending on the cation–anion combination. The elastic constants meet the Born–Huang stability criteria, confirming mechanical robustness. Electronic structure calculations using the TB-mBJ + U approach yield direct band gaps between 0.553 and 1.477 eV, indicating suitability for visible-light absorption. Optical studies reveal strong dielectric polarisation, high refractive indices, and significant absorption coefficients exceeding 10⁴ cm−¹ in the visible region. Thermoelectric analysis shows positive Seebeck coefficients, confirming p-type behaviour, with sulfide analogues exhibiting higher Seebeck values and lower thermal conductivities than their selenide counterparts. These findings highlight the tunability and multifunctional potential of Cu2MSnX4 compounds for high-performance optoelectronic and thermoelectric energy conversion devices.