Quantum Monte Carlo calculations of the energy-level alignment at hybrid interfaces: Role of many-body effects

An approach is presented for obtaining a highly accurate description of the energy-level alignment at hybrid interfaces, using quantum Monte Carlo calculations to include many-body effects as a correction to the standard single-particle picture. For a representative interface between an organic molecule and an inorganic slab, we illustrate the crucial role of many-body effects for correctly describing the energy-level alignment, leading to qualitatively different optoelectronic properties from the prediction within the single-particle description. Further, the heterojunction behavior as a function of quantum confinement in the slab is predicted to be qualitatively different upon inclusion of many-body effects.

Figure 1

(Color online) (a) The isosurfaces of the single-particle states characterizing the energy-level alignments at the organic-inorganic interface. (b) Si(001) slab. (c) ${\text{C}}_8{\text{S}}_4{\text{H}}_8$ molecule.

Figure 2

(Color online) The energy differences, $E\left(N+1\right)-E\left(N\right)$ and $E\left(N\right)-E\left(N-1\right)$, as functions of $1/N$, where $N$ is the number of electrons per supercell of the Si slab shown in Fig. 1b. The solid lines are linear fits to the DFT and QMC values, and the dashed lines indicate the single-particle eigenenergies of VBM and CBM states.

Figure 3

(Color online) The calculated energy-level alignments of the interface from DFT single-particle energies and with many-body effects from QMC. The CBM, VBM, LUMO, and HOMO states correspond to those shown in Fig. 1c.

Figure 4

(Color online) The junction behaviors of the interface as a function of Si-slab thickness, predicted by DFT and QMC. Type “III” refers to the case where the HOMO from the molecular part is essentially equal to or higher in energy than the CBM from the Si slab.