First-principles study of the structural, elastic, and electronic properties of C20, C12B8, and C12N8

摘要

First-principles calculations were performed to study the structural, elastic, and electronic properties of the crystalline form of C20, C12B8, and C12N8. These compounds exhibit very different elastic and electronic properties. The shear modulus of C12N8 is much higher than those of C20 and C12B8. The strong covalent C–N interaction plays an important role in this high shear modulus. Compared with C20, the relatively small Zener anisotropy of C12N8 is mainly due to its large elastic constant (C11 - C12). The calculated band structure shows that C12N8 is an insulator with a direct band gap of 3 eV and the other two compounds (C20 and C12B8) are metallic. Analysis of the band structure, density of states, and charge density show that the degree of filling in the non-bonding 2pz strongly affects the electronic properties. The full filling of the non-bonding orbital for C12N8 results in its insulating behavior.