Accurate Prediction of Band Gaps in Neutral Heterocyclic Conjugated Polymers

Abstract

Heterocyclic π-electron polymers such as polythiophene, polypyrrole, and polyfuran attract wide interest on both experimental and theoretical levels. While the optical properties of these materials are dominated by the band gap, no accurate, reliable computational method currently exists to predict the band gaps of large oligomers. Six computational methods, including ZINDO/CIS, ZINDO/RPA, HF/CIS, HF/RPA, TDDFT/ TDA, and TDDFT are compared here for a set of 60 structurally well-defined heterocyclic oligomers of varied structure. All six methods are compared using both AM1 semiempirical and B3LYP DFT predicted geometries. Among the methods, the semiempirical ZINDO/CIS method applied to DFT-predicted geometries affords the best agreement between computed and experimental band gaps, yielding an RMS error of 0.31 eV over the data set considered. Analysis of the computed band gaps provides a simple, straightforward empirical correction that significantly improves the accuracy of all six methods, with RMS errors between 0.23 eV and 0.44 eV for TDDFT using DFT-predicted geometries and for ZINDO/RPA using AM1-predicted geometries, respectively.

Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

“…17 The latter was recently used to predict band gaps in neutral heterocyclic conjugated polymers showing very good agreement with experimental data. 18 It is important to make clear here that the estimated energy gap from the frontiers molecular orbitals is supported by the Koopmans' theorem based on HF method, 19 including semiempirical approaches, and DFT methods. 20 At DFT level the intrinsic value to E 0 0 can be estimated directly from the eigenvalues of the Kohn-Sham equations, however the accuracy of the predicted properties strongly depends on the approximate exchange-correlation functional.…”

Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory

“…15), nPs (Fig. 17), [108] nTVs [109] or oligoacenes [110] with standard DFT approaches cannot therefore be accessed, whatever the functional (B3LYP, [19,30,[34][35][36][111][112][113][114] BP86, [34,110] B3P86-30 %, [5,36] BLYP, [34,110] SVMN, [19] PB1PBE, [19] LSDA [36] ) or the basis set. [34] Hybrid methods in which the TD-DFT formalism is applied to ground-state geometries optimized at the Hartree-Fock level lead to an overall shift of the calculated transition energies [39] while keeping the overestimated slope in the 1/N representation.…”

Computational Design and Selection of Optimal Organic Photovoltaic Materials

“…This is comparable to those obtained previously with AM1/ZINDO. 50 To test the accuracy of calculated orbital eigenvalues to predict ionization potentials using Koopmans' theorem, we compared the ZINDO orbital eigenvalue for the HOMO to experimental gas-phase vertical ionization energies for 100 compounds. 51 Results are included in the Supporting Information ( Figure S2 and Table S2) and suggest that the ionization potentials show a systematic shift of ∼À0.4 eV relative to experiment; however, because our results compare the difference in two ionization potentials, these shifts will cancel.…”