Probing the geometry of copper and silver adatoms on magnetite: quantitative experiment versus theory

Abstract

Accurately modelling the structure of a catalyst is a fundamental pre- requisite for correctly predicting reaction pathways, but a lack of clear experimental benchmarks makes it di ffi cult to determine the optimal theoretical approach. Here, we utilize the normal incidence X-ray standing wave (NIXSW) technique to precisely determine the three dimensional geometry of Ag 1 and Cu 1 adatoms on Fe 3 O 4 (001). Both adatoms occupy bulk-continuation cation sites, but with a markedly di ff erent height above the surface (0.43 ± 0.03 Å (Cu 1 ) and 0.96 ± 0.03 Å (Ag 1 )). HSE-based calculations accurately predict the experimental geometry, but the more common PBE + U and PBEsol + U approaches perform poorly.