Crystalline ice exists as various stable and metastable allotropes in the real world.In all known crystalline ices except for ice X,water molecules are fully hydrogen bonded to four neighboring water molecules.Inspired by tetrahedral oxygen nets of crystalline ice phases,we propose two series of tetrahedral silicon allotrope candidates,which named as “Ice-D-Si” and “Ice-CL-Si”.They correspond to the dense ice structure and low density clathrate ice structure,respectively.Theoretical calculations based on first principles are performed in order to predict their stabilities,electronic and thermodynamic properties.The stability of all these Ice-D-Si and Ice-CL-Si allotropes is confirmed by computing their equation of states,phonon dispersion and elastic constants.Two direct band gap (~0.6 eV with PBE functional)semiconductors are found among our proposed Ice-D-Si and Ice-CL-Si allotropes.Moreover,we also find the thermal conductivity of Ice-CL-Si allotropes (IcesⅢ-CL-Si)at room temperature is very low(3.9 W/(m·K))owing to their clathrate framework.Their magnitude is only slightly larger than that of vitreous silica(1.36W/(m·K)).The suitable band gap and low thermal conductivity of our new silicon allotropes are anticipated to have applications in photovoltaic and thermoelectric.