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- Keld Lars Bak
- Poul Jørgensen
- Hans Jørgen Aa Jensen, Syddansk universitet ,
- Jeppe Olsen
- Trygve Helgaker, Universitetet i Oslo

A new scheme for obtaining first-order nonadiabatic coupling matrix elements (FO-NACME) for multiconfigurational self-consistent-field (MCSCF) wave functions is presented. The FO-NACME are evaluated from residues of linear response functions. The residues involve the geometrical response of a reference MCSCF wave function and the excitation vectors of response theory. Advantages of the method are that the reference state is fully optimized and that the excited states, represented by the excitation vectors, are strictly orthogonal to each other and to the reference state. In a single calculation the FO-NACME between the reference state and several excited states may be obtained simultaneously. The method is most well suited to describe situations where the dominant configurations for the two states differ mainly by a single electron replacement. When the dominant configurations differ by two electrons many correlating orbitals are required in the MCSCF reference state calculation to accurately describe the FO-NACME. FO-NACME between various states of H _{2}, MgH_{2}, and BH are presented. These calculations show that the method is capable of giving quantitatively correct results that converge to the full configuration interaction limit. Comparisons are made with state-averaged MCSCF results for MgH_{2} and finite-difference configuration interaction by perturbation with multi-configurational zeroth-order wave function reflected by interactive process (CIPSI) results for BH.

Original language | English |
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Journal | The Journal of Chemical Physics |

Volume | 97 |

Issue | 10 |

Pages (from-to) | 7573-7584 |

Number of pages | 12 |

ISSN | 0021-9606 |

Publication status | Published - 1992 |

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ID: 110915299