Density functional theory and Hartree-Fock studies of the geometric and electronic structure of neutral and doped ethylenedioxythiophene (EDOT) oligomers

The geometric and electronic structure of 3,4‐ethylenedioxythiophene oligomers, ranging in size up to the decamer, have been calculated with density functional theory according to Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (DFT/B3LYP/6‐31G) and ab initio Hartree–Fock (HF/6‐31G) methods. A comparison between the energetics of the aromatic and quinoid forms in the neutral state shows as expected that the former is more stable. For both the singly and doubly positively charged compounds, HF is found to localize the excess charge around the center of the molecule, whereas DFT leads to delocalization of the charge all along the conjugated path. The optical properties calculated at the semiempirical level (intermediate neglect of differential overlap/single configuration, (INDO/SCI) on the basis of the geometries provided by DFT and HF are also analyzed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2002