First-principles calculations of the electronic structure and pressure-induced magnetic transition in siderite FeCO₃

Rhombohedral siderite FeCO3 has been studied by using density-functional theory with the generalized gradient approximation (GGA). In order to take into account the strong on-site Coulomb interaction U present in FeCO3, we also performed the GGA+U calculations. We observe a pressure-induced magnetic transition (high spin→low spin) at pressures of 15 and 28 GPa, which are underestimated with respect to the experiment, for the GGA and GGA+U calculations, respectively. This phase transition was with a volume collapse of 10% around, also accompanied by increases in bulk modulus, Young's modulus and sound velocity. The electronic density of states and charge-density calculations revealed that the magnetic transition was due to the pressure-induced Fe3d electron delocalization.