## Abstract

The strong couplings between electronic states in conical intersection regions are among the most challenging problems in quantum chemistry. XMS-CASPT2, a second-order multireference quasidegenerate perturbation theory, has been successful in describing potential energy surfaces near the conical intersections. We have recently proposed a less expensive method for this problem, namely state-interaction pair-density functional theory (SI-PDFT), which considers the coupling between electronic states described by multiconfiguration pair-density functional theory (MC-PDFT). Here we test the accuracy of SI-PDFT for closely coupled potential energy surfaces of methylamine along five different reaction paths for N-H bond fission. We choose paths that pass close to a conical intersection of the ground and first excited states. We find that SI-PDFT predicts potential energy curves and energy splittings near the locally avoided crossing in close proximity to those obtained by XMS-CASPT2. This validates the method for application to photochemical simulations.

Original language | English (US) |
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Pages (from-to) | 13486-13493 |

Number of pages | 8 |

Journal | Physical Chemistry Chemical Physics |

Volume | 21 |

Issue number | 25 |

DOIs | |

State | Published - 2019 |

### Bibliographical note

Funding Information:The authors are grateful to Kelsey Parker for helpful assistance. This work is supported in part by the National Science Foundation under grant no. CHE-1746186.