Ab initio depolarization in self-assembled molecular monolayers: Beyond conventional density-functional theory

We present an efficient ab initio atomic-orbital-based embedding scheme, which allows to describe depolarization effects in self-assembled organic monolayers (SAMs). The method includes periodic-boundary conditions, all multipole moments and local-field effects. Results for substituted oligophenyl SAM, in combination with conventional, hybrid and orbital-dependent density-functional theory (DFT) as well as coupled-cluster (CC) approach, are reported. We find that the accuracy of conventional DFT relies on error cancellation between the concurrent overestimation of dipole and polarizability, but it can yield quantitatively and sometimes even qualitatively wrong results. Hybrid and orbital-dependent functionals strongly improve the overall description and closely reproduce CC results.