Segregation effects on the properties of (AuAg)147Electronic supplementary information (ESI) available: Figure of geometrically decomposed atomic arrangement for Au13Ag134 and Au55Ag92 alloys; table of the differences in Eb and Eexc for all investigated systems, along with EF; plot of EGuptab and EDFTb against σ; plots of the DOS for alloy and core@shell structures with varying Ag : Au ratios. See DOI: 10.1039/c4cp00753k

AuAg nanoclusters are promising supported co-catalysts for photocatalytic hydrogen reduction. However, beyond the quantum regime ( N > 100) little is known about how the electronic properties of these nanoparticles are affected by chemical ordering. We investigate the effects of chemical ordering on the properties of 147-atom cuboctahedral AuAg nanoclusters, using empirical potentials coupled with an atomic-swap basin-hopping search to optimise the elemental distribution, with the lowest energy arrangements then reminimised using Density Functional Theory (DFT). Force-field calculations show Au atoms preferentially occupy sub-surface positions in the bimetallic structures, which results in the formation of a pseudo-onion structure for Ag-rich compositions. At the DFT-level, however, an Ag core surrounded by an Au shell (Ag@Au) is energetically favoured, as electron density can be drawn more readily when Au atoms are positioned on the nanocluster surface, thus resulting in a partial negative charge. Core@shell configurations are analogous to structures that can be chemically synthesised, and further detailed electronic analysis is discussed in the context of nanocluster applications to co-catalysed photocatalysis. AuAg nanoclusters are promising supported co-catalysts for photocatalytic hydrogen reduction.