ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
The electronic and structural properties of the ground and excited states of infinite polydiacetylene chains in acetylenic (PDA) and butatrienic (PBT) structures are studied by a series of ab initio crystalline orbital and linear-combination-of-atomic-orbital periodic density functional theory methods. A complete geometry optimization is performed for PDA and PBT with analytical energy gradient techniques at the Hartree–Fock (HF) and Becke3-Lee-Yang-Parr (B3LYP) levels. The HF/6-31G* and B3LYP/6-31G* reproduce the experimental geometrical parameters of substituted polydiacetylenes with a PDA-like structure. We compute the relative stability and the potential energy curves along the structural transition between PDA and PBT at the HF, B3LYP, and second-order many-body perturbation theory [MBPT(2)] levels. All these calculations predict PDA to be more stable than PBT by 28–87 kJ mol−1. A minimum corresponding to the PBT-like structure is found at the HF level, but not at the B3LYP or MBPT(2) level. We report the frequencies of all the infrared- and Raman-active vibrational modes of PDA at the HF and B3LYP levels. The frequencies of the carbon backbone stretching modes calculated at the B3LYP/6-31G* level are within 60 cm−1 of the measured frequencies of resonance Raman bands, when the former values are scaled by a uniform scale factor of 0.96. The ionization potential (IP), electron affinity (EA), and fundamental band gap (Eg) of PDA are calculated at the HF and B3LYP levels and also at the MBPT(2) level employing the quasiparticle formalism. B3LYP/6-31G* provides the most reasonable IP, EA, and Eg, which are within 0.6 eV of the experimental results. Vertical excitation energies to the lowest singlet and triplet excitons of PDA are obtained by configuration interaction singles and by time-dependent density functional theory employing the B3LYP functional. These treatments properly account for the nonvanishing exciton binding energy. While the CIS/6-31G* excessively overestimates the singlet excitation binding energies, B3LYP/6-31G* provides a value (0.3 eV) that is in good agreement with experiment (0.4 eV). © 2001 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.1368136
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