SBH10: A Benchmark Database of Barrier Heights on Transition Metal Surfaces

While the performance of density functional approximations (DFAs) for gas phase reaction energetics has been extensively benchmarked, their reliability for activation barriers on surfaces is not fully understood. The primary reason for this is the absence of well-defined, chemically accurate benchmark databases for chemistry on surfaces. We present a database of 10 surface barrier heights for dissociation of small molecules, SBH10, based on carefully chosen references from molecular beam scattering, laser assisted associative desorption, and thermal experiments. Our benchmarking study compares the performance of a dispersion-corrected generalized gradient approximation (GGA-vdW), BEEF-vdW, a meta-GGA, MS2, and a screened hybrid functional, HSE06. In stark contrast to gas phase reactions for which GGAs systematically underestimate barrier heights and hybrids tend to be most accurate, the BEEF-vdW functional determines barriers accurately to within 0.14 eV of experiments, while MS2 and HSE06 underestimate barrier heights on surfaces. Higher accuracy of BEEF-vdW stems from the fact that the functional is trained on chemisorption systems, and transition states for dissociation on surfaces closely resemble the final, chemisorbed states. Therefore, a functional that can describe chemisorption accurately can also reliably predict barrier heights on surfaces.