Descriptor for the Efficacy of Aliovalent Doping of Oxides and Its Application for the Charging of Supported Au Clusters

Abstract

We have studied aliovalent doping of oxides, which is central to many applications in technology, using density functional theory (DFT). We consider the following anionic/cationic donor/acceptor dopants in MgO: Al, F, N, P, Li, Na, and K. Not all dopants donate or accept charge to the full extent expected from their nominal oxidation state. Counterintuitively, the charge accepted/donated by a dopant is found to not scale with Δχ alone, where Δχ is the difference in electronegativities between the anion/cation dopant and the cation/anion of the host. Instead, by fitting to a database of our DFT results, we find that the appropriate descriptor is Δχ/, where is the corresponding difference in atomic sizes. We then use to theoretically predict which systems might be most suitable for charging Au monomers or dimers positively or negatively when they are deposited on a doped MgO support. Our results show that at a doping concentration of 2.78%, we are able to tune the charge of Au monomers between −0.84 and +0.21 e and Au dimers between −0.87 and −0.16 e. This is interesting because differently charged Au clusters are optimal catalysts for different chemical reactions.