These surfaces were chosen because of their higher stability compared to others, as will be discussed in the next section. The annotation located in the corners depicts the constituent elements present on the surface for this particular termination. Additionally, the numbers in the index describe the ratio of the corresponding element in the surface. Thereby, surface terminations, containing half the number of oxygen atoms, can be expressed. The side views of the geometries in the supporting information may give a better insight into the annotation. The metal-deficient terminations create an excess of holes due to the surface's missing Cu or Fe atoms. The formation of the midgap states provided by the charge reorganization is known to be a possible mechanism for sustaining polar surface layers. Due to the proximity of the midgap states to the Fermi level, a partial occupation of the p and d states can be suggested.