Rethinking chemisorption: New insights into the factors controlling the binding energy

Chemisorption of atomic and molecular species on a substrate induces electronic charge redistribution upon which substrate nuclei respond by adjusting their positions. This lattice distortion has been linked to the binding energy E$_{\mathrm{B}}$ of the adsorbed species and attached to the so-called surface relaxation energy, E$_{\mathrm{rx}}$. We have found, however, that for transition metals the energy associated with the mere charge redistribution E$_{\mathrm{elec}}$ is much larger than E$_{\mathrm{rx}}$ and thus both contributions must be considered [1]. In this work, we quantify the electronic and structural perturbation energy E$_{\mathrm{P}}$ brought by various adsorbates on surfaces to understand anomalous adsorbate binding energies, i.e., those in which E$_{\mathrm{P}}$ strongly influences the magnitude of E$_{\mathrm{B}}$. For example, for O adsorption on Au(111), while E$_{\mathrm{rx}}$ is only 0.25 eV, the overall perturbation energy E$_{\mathrm{P}}$ affecting E$_{\mathrm{B}}$(O) is $\sim$ 1 eV [1]. This indicates that E$_{\mathrm{P}}$ cannot be ignored but also that local bonds may not be as weak as portrayed by E$_{\mathrm{B}}$, even though E$_{\mathrm{B}}$ is significantly reduced. We expose cases in which E$_{\mathrm{P}}$ is really dominated by the lattice distortion energy, as well as a rationale for its trends as a function of the substrate and adsorbate. We discuss the implications of the fact that E$_{\mathrm{B}}$ is not always predominately controlled by the bond-strength on heterogeneous catalysis, as well as the applications of the same fact. M. Alc\'{a}ntara Ortigoza and S. Stolbov; ``The Perturbation Energy: The missing key to understand gold `nobleness.' '' Submitted in October 2014