Validation of methods for computational catalyst design: Geometries, structures, and energies of neutral and charged silver clusters

We report a systematic study of small silver clusters,Ag_n, Ag_n⁺, and Ag_n^-, n = 1-7. We studied all possible isomers of clusters with n = 5-7. We tested 42 exchange-correlation functionals, and we assess these functionals for their accuracy in three respects: geometries (quantitative prediction of internuclear distances), structures (the nature of the lowest-energy structure, for example, whether it is planar or nonplanar), and energies. We find that the ingredients of exchange-correlation functionals are indicators of their success in predicting geometries and structures: local exchange-correlation functionals are generally better than hybrid functionals for geometries; functionals depending on kinetic energy density are the best for predicting the lowest-energy isomer correctly, especially for predicting two-dimensional to three-dimenstional transitions correctly. The accuracy for energies is less sensitive to the ingredient list. Our findings could be useful for guiding the selection of methods for computational catalyst design.