The mid-level introduces the Hubbard +U correction. (i.e DFT+U, with U= 4eV), where a Coulomb-like interaction is applied only to the 4f valence orbitals of cerium, leading to the PW91+4 approach. This partially corrects the inherent selfinteraction error of semi-local density functionals, which otherwise leads to an incorrect delocalization of strongly correlated d and f electrons. The mid-level of theory also adds a second CeO2 tri-layer to the surface slab model. The geometry of the upper CeO2 trilayer in contact with the platinum oxide is also allowed to relax, while the bottom trilayer remains fixed. The converge parameters are the same as in the low-level relaxation.