Type: Article
Publication Date: 2014-08-26
Citations: 46
DOI: https://doi.org/10.1103/physrevb.90.085141
We investigate charge transfer in prototypical molecular donor-acceptor compounds using hybrid density functional theory (DFT) and the $GW$ approximation at the perturbative level (${G}_{0}{W}_{0}$) and at full self-consistency (sc-$GW$). For the systems considered here, no charge transfer should be expected at large intermolecular separation according to photoemission experiments and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange $\ensuremath{\alpha}$, as for small values of $\ensuremath{\alpha}$ spurious fractional charge transfer is observed between the donor and the acceptor. ${G}_{0}{W}_{0}$ based on hybrid DFT yields the correct alignment of the frontier orbitals for all values of $\ensuremath{\alpha}$. However, ${G}_{0}{W}_{0}$ has no capacity to alter the ground-state properties of the system because of its perturbative nature. The electron density in donor-acceptor compounds thus remains incorrect for small $\ensuremath{\alpha}$ values. In sc-$GW$, where the Green's function is obtained from the iterative solution of the Dyson equation, the electron density is updated and reflects the correct description of the level alignment at the $GW$ level, demonstrating the importance of self-consistent many-body approaches for the description of ground- and excited-state properties in donor-acceptor systems.