  The transfer of charges, including electrons and holes, is a key step in
heterogeneous catalysis, taking part in the reduction and oxidation of
adsorbate species on catalyst surfaces. In plasmonic catalysis, electrons can
transfer from photo-excited metal nanoparticles to molecular adsorbates,
forming transient negative ions that can easily undergo reactions such as
dissociation, desorption, or other chemical transformations. However, ab initio
characterization of these anionic states has proven challenging, and little is
known about the topology of their potential energy surfaces. In this work, we
investigate the dissociative adsorption of HCl on Au(111) as a representative
catalytic process with relatively low reaction probabilities, which could
potentially be enhanced by electron transfer from photo-excited gold
nanoparticles to HCl. We employ projection-based density embedding that
combines the equation-of-motion electron-attachment coupled-cluster singles and
doubles (EOM-EA-CCSD) method with density functional theory (DFT), and build
dissociation curves of HCl$^-$ on Au(111) along the H-Cl bond distance. The HCl
anion in the gas phase is unbound at equilibrium distances and only becomes
bound as the bond stretches. However, our results show that, upon adsorption on
Au(111), HCl$^-$ remains a stable, bound anion at all bond lengths due to
charge delocalization to the metal. Forming bound anions is easier, and
dissociation of HCl$^-$ on Au(111) is further facilitated, with its
dissociation energy reduced by 0.61 eV compared to its neutral counterpart on
Au(111), and by 1.16 eV relative to HCl. These results underscore the efficacy
of embedded EOM-CCSD methods in addressing surface science challenges and
highlight the potential of plasmonic catalysis proceeding via bound, rather
than transient, anionic states.
