Modeling photoelectron spectra of conjugated oligomers with time-dependent density functional theory

Date

2010

Authors

Salzner, U.

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Source Title

Journal of Physical Chemistry A

Print ISSN

1089-5639

Electronic ISSN

1520-5215

Publisher

American Chemical Society

Volume

114

Issue

41

Pages

10997 - 11007

Language

English

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Abstract

With the aim of producing accurate band structures of conjugated systems by employing the states of cations, TDDFT calculations on conjugated oligomer radical cations of thiophene, furan, and pyrrole with one to eight rings were carried out. Benchmarking of density functional theory and ab initio methods on the thiophene monomer shows that the ΔSCF ionization potential (IP) is most accurate at the B3LYP/6-311G* level. Improvement of the basis set beyond 6-311G* leads to no further changes. The IP is closer to experiment at B3LYP/6-311G* than at CCSD(T)/CCPVQZ. For longer oligomers the ΔSCF IPs decrease too fast with increasing chain length with all density functionals. CCSD/6-311G* performs well if the geometries are optimized at the CCSD level. With MP2 geometries IPs decrease too fast. Peak positions in photoelectron spectra were determined by adding appropriate TDDFT excitation energies of radical cations to the ΔSCF IPs. The agreement with experiment and with Green function calculations shows that TDDFT excited states of radical cations at the B3LYP/6-311G* level are very accurate and that absorption energies can be employed to predict photoelectron spectra.

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