Accurate Method for Obtaining Band Gaps in Conducting Polymers Using a DFT/Hybrid Approach

Salzner, Ulrike; Pickup, Peter G.; Poirier, Raymond A.; Lagowski, Jolanta B.

doi:10.1021/jp971652l

Cited by 156 publications

(139 citation statements)

References 60 publications

(102 reference statements)

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“…This basis set has been tested extensively and has been shown to yield reliable results for geometries and excited states of neutral polyenes as well as other conjugated oligomers. 43,[51][52][53][54] As cations and excited states of cations have compact electron densities, 15 this basis set is sufficient for all properties of interest in the present investigation.…”

Section: Methodsmentioning

confidence: 99%

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene

Salzner

2006

J. Chem. Theory Comput.

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Electronic excitations of polyene cations with chain lengths of up to 101 CH units were investigated as model systems for lightly doped polyacetylene (PA). Since high level ab initio calculations such as complete active space perturbation theory (CASPT2) are limited to systems with about 14 CH units, the performances of time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) were evaluated. It turned out that TDDFT excitations energies are much more accurate for polyene cations than for neutral polyenes. The difference between TDHF and TDDFT excitation energies for the first allowed excited state of C 49 H 51 + is only 0.30 eV with pure DFT and 0.21 eV with a hybrid functional. For open-shell systems, pure DFT is found to be superior to DFT-hybrid functionals because it does not suffer from spin-contamination. Pure TDDFT excitation energies and oscillator strengths for small openshell polyene cations compare well with high level ab initio results. Excitation energies are found to be almost independent of the geometry, i.e., the size of the defect. Localization of the defect, however, shifts oscillator strengths from the HOMO-LUMO transition to higher lying excited states of the same symmetry. Lightly doped PA is predicted to exhibit several strong absorptions below 1 eV.

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Section: Methodsmentioning

confidence: 99%

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene

Salzner

2006

J. Chem. Theory Comput.

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“…[5][6][7] The same approach has been used before to reoptimize the B3LYP functional for other sensitive properties. The result is unfortunately property dependent, being 30% HF exchange for excitation energies 25 and 5% HF exchange for NMR chemical shifts. 26 So this is certainly not a universal solution.…”

Section: Density Functionals and The Pairing-energy Problemmentioning

confidence: 99%

Comparison of density functionals for energy and structural differences between the high- [5T2g:(t2g)4(eg)2] and low- [1A1g:(t2g)6(eg)] spin states of iron(II) coordination compounds. II. More functionals and the hexaminoferrous cation, [Fe(NH3)6]2+

Fouqueau

Casida

Daku

et al. 2005

The Journal of Chemical Physics

163

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Comparison of density functionals for energy and structural differences between the high- † 5 T 2g :"t 2g … The ability of different density functionals to describe the structural and energy differences between the high-͓ 5 T 2g :(t 2g ) 4 (e g ) 2 ͔ and low-͓ 1 A 1g :(t 2g ) 6 (e g ) 0 ͔ spin states of small octahedral ferrous compounds is studied. This work is an extension of our previous study of the hexaquoferrous cation, ͓Fe(H 2 O) 6 ͔ 2ϩ , ͓J. Chem. Phys. 120, 9473 ͑2004͔͒ to include a second compound-namely, the hexaminoferrous cation, ͓Fe(NH 3 ) 6 ͔ 2ϩ -and several additional functionals. In particular, the present study includes the highly parametrized generalized gradient approximations ͑GGAs͒ known as HCTH and the meta-GGA VSXC ͓which together we refer to as highly parametrized density functionals ͑HPDFs͔͒, now readily available in the GAUSSIAN03 program, as well as the hybrid functional PBE0. Since there are very few experimental results for these molecules with which to compare, comparison is made with best estimates obtained from second-order perturbation theory-corrected complete active space self-consistent field ͑CASPT2͒ calculations, with spectroscopy oriented configuration interaction ͑SORCI͒ calculations, and with ligand field theory ͑LFT͒ estimations. While CASPT2 and SORCI are among the most reliable ab initio methods available for this type of problem, LFT embodies many decades of empirical experience. These three methods are found to give coherent results and provide best estimates of the adiabatic low-spin-high-spin energy difference, ⌬E LH adia , of 12 000-13 000 cm Ϫ1 for ͓Fe(H 2 O) 6 ͔ 2ϩ and 9 000-11 000 cm Ϫ1 for ͓Fe(NH 3 ) 6 ͔ 2ϩ . All functionals beyond the purely local approximation produce reasonably good geometries, so long as adequate basis sets are used. In contrast, the energy splitting, ⌬E LH adia , is much more sensitive to the choice of functional. The local density approximation severely over stabilizes the low-spin state with respect to the high-spin state. This ''density functional theory ͑DFT͒ spin pairing-energy problem'' persists, but is reduced, for traditional GGAs. In contrast the hybrid functional B3LYP underestimates ⌬E LH adia by a few thousands of wave numbers. The RPBE GGA of Hammer, Hansen, and Nørskov gives good results for ⌬E LH adia as do the HPDFs, especially the VSXC functional. Surprisingly the HCTH functionals actually over correct the DFT spin pairing-energy problem, destabilizing the low-spin state relative to the high-spin state. Best agreement is found for the hybrid functional PBE0. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1839854͔ I. INTRODUCTIONThe identification of the spin symmetry of the ground and low-lying excited states is important for the comprehension of chemical reactivity. However, many interesting cases occur, especially among transition metal coordination compounds, where the competition between the splitting of nearly degenerate orbitals with the electron pairing energy makes the prediction of relative spin-s...

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“…However, such a high level calculation (including electron correlation with a large basis set) for a polymeric system is still restricted to a small unit system in practice. 18 For relatively large systems, [19][20][21][22][23] polymeric structures have been obtained from the calculations on oligomeric structures or from the experimental measurements. Moreover, it is well known that Hartree-Fock level calculations greatly overestimate the HOMO-LUMO gap of a conjugated polymer.…”

Section: Resultsmentioning

confidence: 99%

Molecular Design of Novel Conjugated Polymers for Blue-Light-Emitting Devices

2003

Bulletin of the Korean Chemical Society

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A quantum-chemical study of conformations and electronic structures of polyheterocyclic derivatives with vinylenediheteroatom substituents at the 3-and 4-positions was performed to search for novel blue-lightemitting conjugated polymers. Conformational potential energy curves of the polymers were constructed as a function of the helical angle (a) through semiempirical Hartree-Fock band calculations at the Austin model 1 level. It is found that poly(3,4-vinylenedioxythiophene) possesses a quite flat curve in the range of α = 51.4 o -120 o . Replacing S atoms for O atoms greatly increases repulsion between the neighboring units, and thereby the units become perpendicular to one another. Because of the hydrogen bonding between O and NH, poly(3,4-vinylenedioxypyrrole) is predicted to be anti-coplanar and poly(3,4-vinylenediaminofuran) to be nearly anticoplanar. According to the modified extended Hückel band calculations, the HOMO-LUMO gaps (HLGs) of the polymers, unless the polymer chains are twisted, are close to or slightly smaller than those of their respective mother polymers. Among the polymers, poly(3,4-vinylenedioxythiophene) is presumed to be the most probable candidate for a blue-light emitter because its HLG is within the range of the electronic requirement for blue-light emitters.

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Accurate Method for Obtaining Band Gaps in Conducting Polymers Using a DFT/Hybrid Approach

Cited by 156 publications

References 60 publications

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene

Comparison of density functionals for energy and structural differences between the high- [5T2g:(t2g)4(eg)2] and low- [1A1g:(t2g)6(eg)] spin states of iron(II) coordination compounds. II. More functionals and the hexaminoferrous cation, [Fe(NH3)6]2+

Molecular Design of Novel Conjugated Polymers for Blue-Light-Emitting Devices

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