## Abstract

We investigate the static second hyperpolarizabilities (γ) of tetrathiafulvalene (TTF) and tetrathiapentalene (TTP) using the ab initio molecular orbital (MO) method. The cationic radical states of these systems (TTF^{+}{radical dot} and TTP^{+}{radical dot}) are expected to have large negative γ values, which are rare in organic systems, based on our classification rule of γ. It turns out that at the higher-order electron correlation level TTP^{+}{radical dot} gives a large negative γ value though TTF^{+}{radical dot} gives a positive γ. We also investigate the applicability of the density functional theory (DFT) methods to the calculation of the γ values for these systems. By tuning the mixing parameter of DFT/HF exchange term, a DFT method turns out to semiquantitatively reproduce the γ values of TTP and TTP^{+}{radical dot} at the higher-order electron correlation method, i.e., CCSD(T), while fail in reproducing the γ value of TTF^{+}{radical dot}. This suggests the necessity of further improvement in correlation functional for obtaining reliable γ values of charged radical states.

Original language | English |
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Pages (from-to) | 375-378 |

Number of pages | 4 |

Journal | Synthetic Metals |

Volume | 156 |

Issue number | 5-6 |

DOIs | |

Publication status | Published - 2006 Mar 1 |

Externally published | Yes |

## Keywords

- Conductivity
- Hyperpolarizability
- Nonlinear optics
- Radical

## ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry