When considering subnanoclusters, with only a handful atoms, the situation is more complex because clusters can be fluxional, i.e., have multiple, interconverting, thermally accessible isomers witgh different energies. This means that even for a perfectly monodisperse cluster size distribution (e.g. only clusters of Pt 7 ), isomeric differences in the stability with respect to dissociation may still exist, providing the thermodynamic driving force for sintering. Thus sintering may not be suppressed by size-selection of fluxional clusters. The role of isomeric diversity in accelerating Ostwald ripening of monodisperse Pt n /TiO 2 has previously been shown using a purely theoretical approach. Interestingly, while isomeric diversity did broadly tend to accelerate sintering, size-dependent sintering behavior also became apparent. Some size effects arose due to particular stability of a cluster size, such as Pt 3 /TiO 2 , while others were due to the balance of forward vs. reverse sintering events (e.g., Pt 6 /TiO 2 ). Ultimately, we predicted that certain "magic sinter-resistant" cluster sizes can arise, which should persist longer than other cluster sizes at catalytic temperatures. The work, thus, suggests that the general trend of faster trend of faster sintering for smaller NPs is over-simplified when applied to subnano clusters. . In order to further explore this behavior, we adapted our approach to investigate Pt n /Al 2 O 3 , both with experiment and theory.