Optical and excitonic properties of calcite CaCO3†
Abstract
Calcite has been successfully used as a substrate or coating material in optical devices, but very little is known about its own optical properties. In this study, we present a comprehensive analysis of the optical properties of CaCO3 calcite, a typical representative of metal carbonates, obtained using the density functional theory (DFT), GW, and Bethe–Salpeter equation (BSE) methods. Our findings demonstrate that the onset of the CaCO3 optical spectrum is characterized by bound excitons, with the excitonic wavefunction primarily localized on the CO3 units. We find that calcite exhibits two different types of excitons: a Frenkel-type exciton centered on the CO3 units, leading to a narrow absorption band, and a more delocalized charge-transfer exciton that contributes more significantly to the optical spectra. The excitons exhibit a strong anisotropy with a larger spatial extent in the xy plane, along the layers of the CO3 molecules. Our results provide insight into the electronic structure and reveal the distinctive optical properties of calcite, with further implications for optical applications and the design of nanodevices, where an accurate description of the dielectric properties is required.