System Setup. DFT was used to model N 2 dissociation reaction on Ru(0001). DFT calculations were carried out using the Perdew-Burke-Ernzerhof (PBE) exchange-correlational functional as implemented in the Qbox code. The system was modeled as a nitrogen molecule on a 2x2 unit cell of two-layer Ru(0001) slab with periodic boundary condition in 3D (Figure ). A vacuum spacing of 10 Å in the direction normal to the surface plane was included to avoid interaction across periodic images. The top layer of surface atoms are unfixed; this allows for thermal motion of surface atoms during the reaction. The atoms in the bottom surface layer were held fixed at their equilibrium positions with lattice constants determined by optimizing the bulk lattice. The ion cores were described using Optimized Norm-Conserving Vanderbilt pseudopotentials from the SG15 library , and a plane-wave basis for the valence electrons was used with an energy cutoff of 50 Ry, 2 × 2 × 1 𝑘-point mesh, and Fermi smearing with electronic temperature of 1090 K. PBE tends to over-bind adsorbates to surfaces by a few tenths of eV , and combined with our DFT benchmark studies (Supporting Information), an overall DFT error in predicted barriers can be on the order of tenths of eV.