Energy-driven optoelectronic and mechanical insights into X ₃ GeC (X = Mn, Ni) antiperovskites

In this paper, we present a comprehensive first-principles comparative study of the antiperovskite carbides X 3 GeC (X [Formula: see text] Mn, Ni) using density functional theory within the all-electron WIEN2k and plane-wave CASTEP frameworks. Both compounds adopt a cubic Pm[Formula: see text] structure and satisfy mechanical stability criteria. Optimized lattice parameters are 3.62[Formula: see text]Å (Mn 3 GeC) and 3.79[Formula: see text]Å (Ni 3 GeC), with corresponding densities of 8.70[Formula: see text]g[Formula: see text]cm[Formula: see text] and 7.95[Formula: see text]g[Formula: see text]cm[Formula: see text]. Elastic constant analysis reveals high stiffness for Mn 3 GeC ([Formula: see text][Formula: see text]GPa, bulk modulus [Formula: see text] 235.82[Formula: see text]GPa) and pronounced ductility in Ni 3 GeC ([Formula: see text][Formula: see text]GPa, [Formula: see text][Formula: see text]GPa). Electronic structure calculations (TB-mBJ and HSE06) indicate metallic behavior with zero band gaps. Optical spectra show strong reflectivity ([Formula: see text]%) in the visible–UV range and distinct plasma resonance features, highlighting potential plasmonic applications. Thermoelectric evaluation reveals negative Seebeck coefficients ([Formula: see text][Formula: see text]V[Formula: see text]K[Formula: see text] for Mn 3 GeC; [Formula: see text][Formula: see text]V[Formula: see text]K[Formula: see text] for Ni 3 GeC) with low ZT values. Overall, Mn 3 GeC is mechanically robust, while Ni 3 GeC offers promising optoelectronic and plasmonic functionality.