### 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 - Jan 1 2019 |

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**State-interaction pair density functional theory for locally avoided crossings of potential energy surfaces in methylamine.** / Zhou, Chen; Gagliardi, Laura; Truhlar, Donald G.

Research output: Contribution to journal › Article

*Physical Chemistry Chemical Physics*, vol. 21, no. 25, pp. 13486-13493. https://doi.org/10.1039/c9cp02240f

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TY - JOUR

T1 - State-interaction pair density functional theory for locally avoided crossings of potential energy surfaces in methylamine

AU - Zhou, Chen

AU - Gagliardi, Laura

AU - Truhlar, Donald G

PY - 2019/1/1

Y1 - 2019/1/1

N2 - 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.

AB - 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.

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U2 - 10.1039/c9cp02240f

DO - 10.1039/c9cp02240f

M3 - Article

VL - 21

SP - 13486

EP - 13493

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 25

ER -