Title: Energy Level Alignment at Hybridized Organic-metal Interfaces: the Role of Many-electron Effects,
Abstract: Hybridized molecule/metal interfaces are ubiquitous in molecular and organic
devices. The energy level alignment (ELA) of frontier molecular levels relative
to the metal Fermi level (EF) is critical to the conductance and functionality
of these devices. However, a clear understanding of the ELA that includes
many-electron self-energy effects is lacking. Here, we investigate the
many-electron effects on the ELA using state-of-the-art, benchmark GW
calculations on prototypical chemisorbed molecules on Au(111), in eleven
different geometries. The GW ELA is in good agreement with photoemission for
monolayers of benzene-diamine on Au(111). We find that in addition to static
image charge screening, the frontier levels in most of these geometries are
renormalized by additional screening from substrate-mediated intermolecular
Coulomb interactions. For weakly chemisorbed systems, such as amines and
pyridines on Au, this additional level renormalization (~1.5 eV) comes solely
from static screened exchange energy, allowing us to suggest computationally
more tractable schemes to predict the ELA at such interfaces. However, for more
strongly chemisorbed thiolate layers, dynamical effects are present. Our ab
initio results constitute an important step towards the understanding and
manipulation of functional molecular/organic systems for both fundamental
studies and applications.