## Résumé

Ab initio calculations, including the electron correlation effects via the Moller-Plesset partitioning, of the static longitudinal polarizability (α_{L}), first and second hyperpolarizabilities ( β_{L} and γ_{L}) of small push-pull molecules have been carried out with the 6-31G and 6-31G* basis sets. Two types of conjugated segment (polyacetylene and polyyne) were used as linker between the nitro and amino fragments, chosen as acceptor and donor groups. For small chains, the triply bonded structures lead to larger γ_{L} than the doubly bonded structures, although the α_{L} and β_{L} values order in the opposite direction. The second-order Møller-Plesset (MP2) corrections are essential to obtain correct estimates of the hyperpolarizabilities and are generally much larger than the MP3 and MP4 contributions. Geometry optimizations were carried out with both basis sets within the Hartree-Fock and MP2 schemes; the MP2 geometries lead to smaller bond length alternations and thus larger (hyper)polarizabilities. For α_{L} careful choice of the geometry is more crucial than the use of polarization functions during the electronic state calculations; however, for the hyperpolarizabilities, both the geometry and the basis set are of importance.

langue originale | Anglais |
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Pages (de - à) | 679-688 |

Nombre de pages | 10 |

journal | International Journal of Quantum Chemistry |

Volume | 65 |

Numéro de publication | 5 |

Etat de la publication | Publié - 1 déc. 1997 |