Structural stabilities and optical properties of SixGeyHz nanocrystals

Based on the high-throughput first-principles calculations with structural recognition, we have ystematically investigated the structural stabilities and optical properties of Si_xGe_yH_z nanocrystals(H-SiGeNCs), including various sizes, shapes and compositions. The total energies of H-SiGeNCs can be simply estimated by the bond energy model in high accuracy, where the error of test set is less than 0.5 meV per atom. According to the energy difference of Si/Ge in various bonding environments, we have determined the ground state structures by the geometry analysis, as is confirmed the convex hulls of formation enthalpy from the first-principles calculations. In addition, the energy gaps of H-SiGeNCs are modulated by the atomic distributions, as well as the vibrations of Si-H and Ge-H bonds at room temperature which is revealed by ab initio molecular dynamics simulations.