## Abstract

The spin-restricted formulas for the analytical gradients of the second-order Møller-Plesset perturbation (MP2) energy are presented within the framework of ab initio crystal orbital theory of infinite one-dimensional lattices (polymers). The coupled perturbed Hartree-Fock equation for polymers is solved iteratively using the atomic-orbital-based algorithms. The MP2 energy and its gradient contributions are evaluated by the disk-based algorithms with the aid of the two-particle density matrix. The analytical-gradient method at the MP2 level, as well as the analytical first- and second-derivative methods at the Hartree-Fock (HF) level, is applied to calculate the equilibrium structures and harmonic vibrational frequencies of all-trans polyacetylene. The deviations of the calculated frequencies from the observed ones for the in-phase C=C stretching modes are reduced by about 70% on going from HF/6-31G to MP2/6-31G theory.

Original language | English (US) |
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Pages (from-to) | 4147-4155 |

Number of pages | 9 |

Journal | Journal of Chemical Physics |

Volume | 109 |

Issue number | 11 |

DOIs | |

State | Published - 1998 |

Externally published | Yes |

## ASJC Scopus subject areas

- Physics and Astronomy(all)
- Physical and Theoretical Chemistry