### Abstract

An analytic energy gradient method for second-order quasidegenerate perturbation theory with multiconfigurational self-consistent field reference functions (MC-QDPT) is derived along the lines of the response function formalism (RFF). According to the RFF, the gradients are calculated without solving coupled perturbed equations. Instead, it is necessary to solve seven sets of linear equations in order to determine Lagrangian multipliers, corresponding to four sets of parameter constraining conditions and three sets of additional parameter defining conditions in the Lagrangian. Just one of these linear equations is a large scale linear equation; the others are reducible to just partial differentiations or simple equations solvable by straightforward subroutines.

Original language | English |
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Pages (from-to) | 5660-5669 |

Number of pages | 10 |

Journal | Journal of Chemical Physics |

Volume | 108 |

Issue number | 14 |

DOIs | |

Publication status | Published - Apr 8 1998 |

Externally published | Yes |

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### All Science Journal Classification (ASJC) codes

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

### Cite this

*Journal of Chemical Physics*,

*108*(14), 5660-5669. https://doi.org/10.1063/1.475975