Pressure-Induced Mechanical Instabilities in Cubic SiC: Structural and Electronic Properties

Silicon carbide is widely used in electronics, ceramics, and renewable energy due to its exceptional hardness and resistance. In this study, we investigate the effects of hydrostatic and uniaxial pressure (both compressive and tensile) on the structural and electronic properties of $3C$-SiC. Our analysis is based on atomistic molecular dynamics (MD) simulations using an efficient tight-binding Hamiltonian, whose accuracy is validated against density functional theory calculations. Moreover, to account for nuclear quantum effects, we employ path-integral MD simulations. Our results show significant changes in the direct electronic gap as a function of temperature and pressure, with a renormalization of about 80 meV due to zero-point motion. Under hydrostatic tensile pressure, the direct band gap $E_{\Gamma}$ vanishes at the material's mechanical stability limit (spinodal point, where the bulk modulus $B \to 0$). For uniaxial pressure, we observe instabilities (Young's modulus $Y \to 0$) at approximately 90 GPa for both tension and compression, where $E_{\Gamma} \to 0$. Additionally, we analyze the pressure dependence of the internal energy, lattice parameter, and bond length, along with their finite-temperature fluctuations, which exhibit anomalies near the instability points.