Electronic structures of siderite (FeCO3) and rhodochrosite (MnCO3): Oxygen K-edge spectroscopy and hybrid density functional theory

Electronic transitions of siderite and rhodocrosite may have played a role in prebiotic synthesis by photochemical reactions in the Archean. In the work described here, I measured the electronic structures of siderite (FeCO3) and rhodocrosite (MnCO3) using O K-edge X-ray absorption and emission spectroscopy. At the same time, I present theoretical calculations of electronic structure using periodic density functional theory with several different exchange correlation functionals. To help verify the reliability of the basis sets and the exchange correlation functionals, I determined the optimized crystal structures of FeCO3 and MnCO3 in the antiferromagnetic (AF) rhombohedral unit cell. All three exchange-correlation functionals give static volumes and cell parameters that differ from experiment by <2%.