Effect of spin contamination error on surface catalytic reaction: NO reduction by core-shell catalysts

The effects of spin contamination errors on the activation barriers of catalytic NO reduction by TiO2/Ag and ZrO2/Cu core-shell catalyst models were investigated using an approximate spin projection method and an unrestricted density functional theory calculation with the plane-wave basis set. The estimated barrier of the TiO2/Ag system increased (0.03 eV), whereas that of the ZrO2/Cu system decreased (0.04 eV) after the correction of the spin contamination error. This difference in the estimated barriers of the two systems can be attributed to the difference in their surface structures. The error obtained for the TiO2/Ag system was larger than that obtained for the gas phase, i.e. the spin contamination error was induced by the molecule/surface interaction. Moreover, the error correction also changed the rate-determining step of ZrO2/Cu. These results demonstrate the importance of the correction of spin contamination errors for the detailed investigation of catalytic reactions.