### Abstract

The mathematical constructs of the Dyson coordinates and geometry are introduced. The former are a unitary transformation of the normal coordinates and the anharmonic vibrational counterpart of the Dyson orbitals in electronic structure theory. The first-order Dyson coordinates bring the sums of the harmonic force constants and their first-order diagrammatic perturbation corrections (the first-order Dyson self-energy) to a diagonal form. The first-order Dyson geometry has no counterpart in electronic structure theory. It is the point on the potential energy surface at which the sums of the energy gradients and their first-order diagrammatic perturbation corrections vanish. It agrees with the vibrationally averaged geometry of vibrational self-consistent field (VSCF) theory in the bulk limit. These constructs provide a unified view of the relationship of VSCF and its diagrammatically size-consistent modifications as well as the self-consistent phonon method widely used in solid-state physics.

Original language | English (US) |
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Pages (from-to) | 7179-7189 |

Number of pages | 11 |

Journal | Journal of Physical Chemistry A |

Volume | 117 |

Issue number | 32 |

DOIs | |

State | Published - Aug 15 2013 |

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## Cite this

*Journal of Physical Chemistry A*,

*117*(32), 7179-7189. https://doi.org/10.1021/jp4008834