First-principles description of charge transfer in donor-acceptor compounds from self-consistent many-body perturbation theory

Abstract

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 α, as for small values of α 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 α. 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 α 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.

Enforcing the linear behavior of the total energy with hybrid functionals: Implications for charge transfer, interaction energies, and the random-phase approximation

“…In this approach, α is determined by requiring that the self-energy correction to the HOMO level within the G 0 W 0 approximation [11] is minimized. Eventually, this also fixes the starting point dependence of the perturbative GW approximation [12][13][14]. the local exchange potential in the PBE approximation [6].…”

Generalization of Dielectric-Dependent Hybrid Functionals to Finite Systems

“…(8) predicted Δ > 0, with ε TCNQ LUMO ¼ −4.32 and ε TTF HOMO ¼ −6.15 eV. The mixing fraction that minimizes the deviation from the straight-line error was shown to be 0.70 for TCNQ and 0.8 for TTF [77,78], not dissimilar from the values predicted by Eq. (8).…”

Quasi-particle energy spectra in local reduced density matrix functional theory

“…Marom et al 26 Table I compared with experimental results. the performance of a hierarchy of GW approximations for benzene, pyridine, and the diazines and compared the quasiparticle spectrum with PES. Caruso and co-workers [27][28][29] developed an all electron implementation of self-consistent GW (sc-GW ) with localized basis functions and showed that it is more accurate than other approximations lower in GW hierarchy. They applied sc-GW on five molecules relevant for organic photovoltaics 28 obtaining an average error of 0.4 eV (maximum error 1.2 eV).…”

“…Those calculations suffer from a strong initial state dependence and the good agreement found could be just fortuitous. In this context, self-consistent GW [27][28][29] was found to systematically improve ionization energies and total energies of closed shell systems. The single electron spectral properties are in very close agreement with experiment avoiding the starting-point dependence.…”

“…The Perdew-Zunger self-interaction correction (SIC) method 17 in DFT offers a correction to this problem and was found to yield orbital energies closer to the experimental IPs 18 improving several other properties as well. [18][19][20] The GW method [21][22][23] was initially introduced to improve the obtained quasiparticle spectrum of solids but in the last decade, GW at various levels of approximations was also applied to finite systems [24][25][26][27][28][29][30] improving significantly the quasiparticle excitation energies with respect to standard DFT-approximations. Those calculations suffer from a strong initial state dependence and the good agreement found could be just fortuitous.…”