Metal nanoclusters supported on oxide surfaces are widely-used catalysts that
boasts sharply enhanced activity over their bulk, especially for the coinage
metals: Au, Ag and Cu. These properties depend sensitively on the nanocluster
structure, which are challenging to model with density functional theory (DFT)
-- the workhorse modelling technique. Leveraging the recently developed SKZCAM
protocol, we perform the first ever benchmark study of coinage metal structures
on the MgO surface with coupled cluster theory [CCSD(T)] -- the gold-standard
modelling technique. We investigate a comprehensive range of DFT models
(exchange-correlation functional and dispersion correction) and our benchmarks
reveal that none of the investigated models can accurately describe this
system. We demonstrate that this arises from inadequate account of metal-metal
interactions in the nanocluster and propose a high-level correction which
provides reference accuracy at low cost. This forges a path towards studying
larger systems, which we highlight by benchmarking Au20​ on MgO, a
challenging system where DFT models have disagreed on its ground state
structure.Comment: Working pape