Mechanical, Optical, and Thermoelectric Properties of Metastable Silicon oP16-Si: A First-Principles Study

Using the coordination-constrained searching strategy implemented in RG2 software, a novel metastable silicon crystal named oP16-Si, which hosts lower energy compared to the previously synthesized Si24 is reported. The first-principles calculations further confirm its dynamic, mechanical, and thermodynamic stabilities, indicating the potential for experimental synthesis. The corresponding characterization of the Raman spectrum and eigenvibration vectors is calculated for experimental identification as well. The analysis of its mechanical properties indicates that the material has a hardness of 24.88 GPa and a Poisson's ratio of 0.24, classifying it as highly hard and brittle. More interestingly, calculations demonstrate that the oP16-Si exhibits a bandgap of 1.41 eV, and it has a broader absorption spectrum than diamond silicon. By combining with Boltzmann transport theory, the thermal and thermoelectric performance of oP16-Si are investigated. The results reveal that the four-phonon interaction significantly influences the thermal transport performance of oP16-Si, with an average lattice thermal conductivity of 16.88 W mK-1 at 300 K, contributing to its exceptional thermoelectric figure of merit, peaking at 1.42 with p-type doping. These findings shed light on the physical properties of this novel metastable silicon and foreshadow its potential applications in photovoltaic and thermoelectric.