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Outer-valence Electron Spectra of Prototypical Aromatic Heterocycles from an Optimally Tuned Range-Separated Hybrid Functional.

Egger DA, Weissman S, Refaely-Abramson S, Sharifzadeh S, Dauth M, Baer R, Kümmel S, Neaton JB, Zojer E, Kronik L - J Chem Theory Comput (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Solid State Physics, Graz University of Technology , 8010 Graz, Austria ; Department of Materials and Interfaces, Weizmann Institute of Science , Rehovoth 76100, Israel.

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.

No MeSH data available.


Simulated DFT and GWspectra (see text for details), obtained fromcomputed energy levels (shown as sticks) by broadening via convolutionwith a 0.15-eV-wide Gaussian. PBE, PBE0, and GW data were taken fromref (69). Theoreticaldata are compared to the experimental gas phase photoemission dataof Evangelista et al.141 and to the thinfilm inverse photoemission data of (a) Murdey et al.142 (shown with curve fitting results) and (b) Hill et al.143 The experimental inverse photoemission spectrawere shifted so as to align the LUMO peak with the computed GW@PBE0LUMO peak. On the OT-RSH data, optimal γ values are given inBohr–1. Eigenvalues corresponding to the eg, a1u, and b1g orbitals are designated by the same color scheme as in Figure 8.
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fig9: Simulated DFT and GWspectra (see text for details), obtained fromcomputed energy levels (shown as sticks) by broadening via convolutionwith a 0.15-eV-wide Gaussian. PBE, PBE0, and GW data were taken fromref (69). Theoreticaldata are compared to the experimental gas phase photoemission dataof Evangelista et al.141 and to the thinfilm inverse photoemission data of (a) Murdey et al.142 (shown with curve fitting results) and (b) Hill et al.143 The experimental inverse photoemission spectrawere shifted so as to align the LUMO peak with the computed GW@PBE0LUMO peak. On the OT-RSH data, optimal γ values are given inBohr–1. Eigenvalues corresponding to the eg, a1u, and b1g orbitals are designated by the same color scheme as in Figure 8.

Mentions: To understand the manifestation of the SIE (and its mitigation)in the simulated photoelectron data, spectra computed with differentcomputational methods are compared to experimental photoemission datain Figure 9. Importantly, in this figure wecompare occupied-state eigenvalues to the gas-phase photoelectronspectrum as before, but further compare unoccupied-state eigenvaluesto experimental inverse photoemission spectroscopy(IPES). In IPES, photons are emitted from a sample due to its irradiationwith fixed-energy electrons, and the energy distribution of the emittedphotons is measured, yielding experimental information on virtualstates.1 CuPc is the first system in thisarticle for which such comparison is possible, because for the smallaromatic rings the virtual states are unbound and because for 3N-thiolno (regular or inverse) experimental PES data are available. In fact,gas-phase inverse photoemission spectroscopy is nonexistent in general.Therefore, the comparison is to experimental data obtained from thinCuPc films. Due to polarization effects,59,134,135 the electron affinity of a filmis much smaller than that of an isolated molecule, and the computedempty state energies and the measured inverse photoemission spectroscopydata can be compared only up to a rigid shift. Therefore, to allowcomparison to experimental results without modifying the computationalgas-phase data, the experimental IPES spectra were shifted so as toalign the lowest-energy peak with the GW spectrum shown at the topmostcomputed spectrum in Figure 9.


Outer-valence Electron Spectra of Prototypical Aromatic Heterocycles from an Optimally Tuned Range-Separated Hybrid Functional.

Egger DA, Weissman S, Refaely-Abramson S, Sharifzadeh S, Dauth M, Baer R, Kümmel S, Neaton JB, Zojer E, Kronik L - J Chem Theory Comput (2014)

Simulated DFT and GWspectra (see text for details), obtained fromcomputed energy levels (shown as sticks) by broadening via convolutionwith a 0.15-eV-wide Gaussian. PBE, PBE0, and GW data were taken fromref (69). Theoreticaldata are compared to the experimental gas phase photoemission dataof Evangelista et al.141 and to the thinfilm inverse photoemission data of (a) Murdey et al.142 (shown with curve fitting results) and (b) Hill et al.143 The experimental inverse photoemission spectrawere shifted so as to align the LUMO peak with the computed GW@PBE0LUMO peak. On the OT-RSH data, optimal γ values are given inBohr–1. Eigenvalues corresponding to the eg, a1u, and b1g orbitals are designated by the same color scheme as in Figure 8.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4020925&req=5

fig9: Simulated DFT and GWspectra (see text for details), obtained fromcomputed energy levels (shown as sticks) by broadening via convolutionwith a 0.15-eV-wide Gaussian. PBE, PBE0, and GW data were taken fromref (69). Theoreticaldata are compared to the experimental gas phase photoemission dataof Evangelista et al.141 and to the thinfilm inverse photoemission data of (a) Murdey et al.142 (shown with curve fitting results) and (b) Hill et al.143 The experimental inverse photoemission spectrawere shifted so as to align the LUMO peak with the computed GW@PBE0LUMO peak. On the OT-RSH data, optimal γ values are given inBohr–1. Eigenvalues corresponding to the eg, a1u, and b1g orbitals are designated by the same color scheme as in Figure 8.
Mentions: To understand the manifestation of the SIE (and its mitigation)in the simulated photoelectron data, spectra computed with differentcomputational methods are compared to experimental photoemission datain Figure 9. Importantly, in this figure wecompare occupied-state eigenvalues to the gas-phase photoelectronspectrum as before, but further compare unoccupied-state eigenvaluesto experimental inverse photoemission spectroscopy(IPES). In IPES, photons are emitted from a sample due to its irradiationwith fixed-energy electrons, and the energy distribution of the emittedphotons is measured, yielding experimental information on virtualstates.1 CuPc is the first system in thisarticle for which such comparison is possible, because for the smallaromatic rings the virtual states are unbound and because for 3N-thiolno (regular or inverse) experimental PES data are available. In fact,gas-phase inverse photoemission spectroscopy is nonexistent in general.Therefore, the comparison is to experimental data obtained from thinCuPc films. Due to polarization effects,59,134,135 the electron affinity of a filmis much smaller than that of an isolated molecule, and the computedempty state energies and the measured inverse photoemission spectroscopydata can be compared only up to a rigid shift. Therefore, to allowcomparison to experimental results without modifying the computationalgas-phase data, the experimental IPES spectra were shifted so as toalign the lowest-energy peak with the GW spectrum shown at the topmostcomputed spectrum in Figure 9.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Solid State Physics, Graz University of Technology , 8010 Graz, Austria ; Department of Materials and Interfaces, Weizmann Institute of Science , Rehovoth 76100, Israel.

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.

No MeSH data available.