Abstract
Density functional theory with optimally tuned range-separated hybrid (OT-RSH) functionals has been recently suggested [Refaely-Abramson et al. Phys. Rev. Lett.2012, 109, 226405] as a nonempirical approach to predict the outer-valence electronic structure of molecules with the same accuracy as many-body perturbation theory. Here, we provide a quantitative evaluation of the OT-RSH approach by examining its performance in predicting the outer-valence electron spectra of several prototypical gas-phase molecules, from aromatic rings (benzene, pyridine, and pyrimidine) to more complex organic systems (terpyrimidinethiol and copper phthalocyanine). For a range up to several electronvolts away from the frontier orbital energies, we find that the outer-valence electronic structure obtained from the OT-RSH method agrees very well (typically within ∼0.1–0.2 eV) with both experimental photoemission and theoretical many-body perturbation theory data in the GW approximation. In particular, we find that with new strategies for an optimal choice of the short-range fraction of Fock exchange, the OT-RSH approach offers a balanced description of localized and delocalized states. We discuss in detail the sole exception found—a high-symmetry orbital, particular to small aromatic rings, which is relatively deep inside the valence state manifold. Overall, the OT-RSH method is an accurate DFT-based method for outer-valence electronic structure prediction for such systems and is of essentially the same level of accuracy as contemporary GW approaches, at a reduced computational cost.
Highlights
Many electronic properties of molecules and materials are determined by and understood through the energetics of the valence electrons, which are often probed experimentally using photoemission spectroscopy (PES).[1]
We examined the performance of optimally tuned range-separated hybrid functionals for predicting the photoemission spectra of several challenging prototypical and complex (3N-thiol and CuPc)cyclic organic molecules
Our self-interaction corrected (SIC) calculations confirmed that self-interaction errors can be efficiently mitigated in optimally tuned range-separated hybrid (OT-range-separated hybrid (RSH)) functionals, which shows that, with a PBE0-based optimal choice of the short-range fraction of Fock exchange, the OT-RSH method can offer an excellent balance in the description of localized and delocalized states
Summary
Many electronic properties of molecules and materials are determined by and understood through the energetics of the valence electrons, which are often probed experimentally using photoemission spectroscopy (PES).[1]. With the obtained overall very encouraging results at hand, we proceed toward larger and more complex systems, here chosen to be terpyrimidinethiol and copper phthalocyanine (3N-thiol and CuPc, see Figure 1b) These molecules, which contain N as a heteroatom, are interesting for novel applications in organic electronics[63−68] but at the same time challenging to assess theoretically due to pronounced differences in SIE among the high-lying orbitals in the valence electron spectrum.[34,68,69] Through a comparison to GW calculations and/or PES experiments, we show that OT-RSH can provide accurate valence-electron spectra for these more complex organic systems, with an optimal choice for the short-range Fock exchange that is guided by conventional hybrid functional calculations. Our results clearly demonstrate that OT-RSH functionals are a highly promising, state-of-theart approach for predicting ionization spectra of gas-phase organic molecules
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