Electronic and optical properties of CaCO3 calcite, and excitons in Si@ CaCO3 and CaCO3@ SiO2 core-shell quantum dots

Density functional theory calculations of the electronic and optical properties of the CaCO3 calcite polymorph were performed within both the local density (LDA) and generalized gradient (GGA) approximations, respectively. The carriers effective masses are estimated, and the energy gap is shown to be indirect, with E-G(D -> Z)(LDA) = 4.95 eV and E-G(D -> Z)(GGA) = 5.07 eV ( for comparison, the experimental value is 6.0 +/- 0.35 eV). Two optical absorption regimes are predicted, and the dielectric function does not change considerably with the light polarization. The confinement features of excitons in Si@ CaCO3 and CaCO3@ SiO2 spherical core-shell quantum dots are also presented.