Mechanical Anisotropic and Electronic Properties of Amm2-carbon under Pressure

Structural, electronic properties and mechanical anisotropy of Amm2-carbon are investigated utilizing first-principles calculations by Cambridge Serial Total Energy Package (CASTEP) code. The work is performed with the generalized gradient approximation in the form of Perdew Burke Ernzerhof (PBE), PBEsol, Wu and Cohen (WC) and local density approximation in the form of Ceperley and Alder data as parameterized by Perdew and Zunger (CA-PZ). The mechanical anisotropy calculations show that Amm2-carbon exhibit large anisotropy in elastic moduli, such as Poisson's ratio, shear modulus and Young's modulus, and other anisotropy factors, such as the shear anisotropic factor and the universal anisotropic index A(U). It is interestingly that the anisotropy in shear modulus and Young's modulus, universal anisotropic index and the shear anisotropic factor all increases with increasing pressure, but the anisotropy in Poisson's ratio decreases. The band structure calculations reveal that Amm2-carbon is a direct-band-gap semiconductor at ambient pressure, but with the pressure increasing, it becomes an indirect-band-gap semiconductor.