Cluster structures from DFT. Figure shows the thermally accessible isomers for (Fig. ) Pt4/α-Al2O3 and (Fig. ) Pt4Ge/α-Al2O3 calculated using global optimization at the DFT level, as described in the methods section. The predicted isomer populations at 700 K, near the upper end of the experimental temperature range, are given as P700K. For Pt4/alumina, the global minimum structure (GM) is a spin-singlet, but all other thermally-accessible local minima (LM) are spin-triplets. The structures have Pt atoms with both positive and negative charges, but in all cases, there is net support-to-cluster electron transfer (ΔQ). For Pt4Ge/alumina, the GM and all thermally accessible LMs are singlets, with substantial Ge-to-Pt4 electron transfer, they also all have net support-to-cluster electron transfer.