Si₉₆: A New Silicon Allotrope with Interesting Physical Properties

The structural mechanical properties and electronic properties of a new silicon allotrope Si₉₆ are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si₉₆ is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si₉₆ are at the R and G point, which indicates that Si₉₆ is an indirect band gap semiconductor. The anisotropic calculations show that Si₉₆ exhibits a smaller anisotropy than diamond Si in terms of Young's modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index A^U. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si₉₆ quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials.