## Abstract

We used multiconfiguration quasidegenerate perturbation theory and the fourfold-way direct diabatization scheme to calculate ab initio potential-energy surfaces at 3600 nuclear geometries of NH3. The calculations yield the adiabatic and diabatic potential-energy surfaces for the ground and first electronically excited singlet states and also the diabatic coupling surfaces. The diabatic surfaces and coupling were fitted analytically to functional forms to obtain a permutationally invariant 2×2 diabatic potential-energy matrix. An analytic representation of the adiabatic potential-energy surfaces is then obtained by diagonalizing the diabatic potential-energy matrix. The analytic representation of the surfaces gives an analytic representation of the four-dimensional conical intersection seam which is discussed in detail.

Original language | English (US) |
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Article number | 124309 |

Journal | Journal of Chemical Physics |

Volume | 124 |

Issue number | 12 |

DOIs | |

State | Published - 2006 |

### Bibliographical note

Funding Information:The authors thank Hisao Nakamura for helpful discussions. This work was supported in part by the National Science Foundation under Grant No. CHE03-49122 and by the Office of Naval Research under Grant No. ONR-N00014-01-1-0235.