Prediction of the Rb-Si compounds under high pressure

Abstract

Using a global structure prediction method, we explored the structures, stability, and electronic properties of binary Rb-Si compounds under high pressure. We identified eight rubidium silicides, which are dynamically stable in their stable pressure region. We also identified five novel silicon allortopes via removing the Rb atoms from the predicted Rb-Si compounds. Two new silicon allotropes, Cmcm-Si and C2/m-Si, were first proposed, which are both dynamically and mechanically stable. Electronic structure calculations reveal that Cmcm-Si is a semiconductor with direct bandgap and C2/m-Si exhibits metallicity. Besides, the Cmcm-Si phase demonstrates that its optical properties are superior to that of dia-Si, indicating it could be a promising photovoltaic material. The present results expand the high pressure phases of Rb-Si compounds and provide insights for exploring other alkali silicides with open channels.