Understanding Trends in Catalytic Activity: The Effect of Adsorbate–Adsorbate Interactions for CO Oxidation Over Transition Metals

Self-consistent, periodic density functional theory (DFT) calculations were performed using the Dacapo total energy code using the RPBE exchange-correlation functional [53]. Ultrasoft Vanderbilt pseudopotentials are used to describe the core electrons and the Kohn-Sham one electron valence states are expanded in a plane wave basis set with a kinetic energy cutoff below 408 eV [54]. The electron density is determined by iterative diagonalization of the Kohn-Sham Hamiltonian, Fermi population of the Kohn-Sham states (k_bT = 0.1 eV), and Pulay mixing of the resulting electron density [55]. Total energies are then extrapolated to k_bT = 0 eV [56]. Sampling of the surface Brillouin zone was done using a 6 × 4 × 1 Monkhorst-Pack k-point set [57]. Fcc(111) surfaces of Au, Ag, Cu, Pd, Pt, Ni, and Rh were modeled as slabs with a (2 × 3) unit cell and four atomic layers. A vacuum of 10 Å separates successive slabs along the normal direction of the surface. The top two layers were allowed to relax, while the bottom two layers were kept fixed in their bulk truncated positions