Ab initio study of structural, electronic and optical properties of Calcium Carbonate compound

In this paper, the structural , electronic and optical  properties of calcium carbonate in hexagonal (calcite) ,orthorhombic (aragonite)  and orthorhombic( waterite)phases are investigated.The calculations have been performed with pseudopotential methodin the framework of the density functional theory with different approximations and using Quantum Espresso package.The band structure results for the calcium carbonate compound in the hexagonal phase indicate an indirect band gap in the  direction and the orthorhombic phase has a direct band gap.The refractive index obtained for the hexagonal phase in the and  directions are 1.45 and 1.27, respectively. The obtained refractive index for orthorhombic phase in and  directions are 1.48, 1.45 and 1.36, respectively. Also, the value of the optical gap for orthorhombic and hexagonal phases in and directions have been calculated. The obtained results are in good agreement with other available data.