Systematic Exploration of Minimum Energy Conical Intersection Structures near the Franck–Condon Region

Abstract

Locating accessible conical intersections (CIs), especially minimum energy CI (MECI) structures, near the Franck-Condon (FC) region is one of the most important tasks in theoretical analyses of photoreactions. Many MECIs may exist around a FC point in molecules with many vibrational degrees of freedom. Usually, MECIs are optimized one by one starting from arbitrary chosen initial structures. In order to eliminate the arbitrariness, we have developed automated MECI search methods. In this paper, a new approach is described. It combines the seam model function approach with the recently proposed single-component artificial force induced reaction method. Starting from a FC point, the present method finds MECIs systematically. It requires neither a Hessian nor a derivative coupling vector. In an example of the automated search, the spin-flip TDDFT was employed as an efficient electronic structure calculation method, which, together with an automated algorithm to recognize proper electronic states, allowed for evaluation of energy and gradient in a black-box fashion. The present approach was tested with trans- and cis-1,3-butadiene, thymine, and coumarin molecules. The usefulness of the present approach was demonstrated by comparing obtained MECIs with those in the literature. It is hoped that the present technique will be useful in exploration of unknown photoreaction pathways.

Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

“…PESs upon extending one C-O bond, 132 yet TA and TRIR absorption studies following UV excitation in this case reveal essentially 100% parent bleach recovery within 100 ps and no ring-opened products 129,133 -reminding us that the product branching is likely to depend not just on the geometry of, but also the nuclear momenta on passage through, the regions of conical intersection between PESs.…”

Implementation and performance of the artificial force induced reaction method in the GRRM17 program

“…In GRRM17, structures of MESX and MECI can be explored by the SC-AFIR method. [66,67] MESX is a local minimum on the crossing seam between two adiabatic PESs of different spin or space symmetry. MECI is a local minimum on the conical intersection between two adiabatic PESs of the same spin and space symmetry.…”

Exploration of minimum energy conical intersection structures of small polycyclic aromatic hydrocarbons: toward an understanding of the size dependence of fluorescence quantum yields

“…20 Recently, its applicability has been improved dramatically by the use of the spin-flip time dependent density functional theory (SF-TDDFT) [21][22][23] in the electronic structure calculations, and the use of the singlecomponent artificial force induced reaction (SC-AFIR) 24 method in the automated stable structure search. 25,26 In the present study, MECI geometries for the lowest two singlet electronic states (denoted S 1 /S 0 -MECI) were systematically searched using the SMF/SC-AFIR/SF-TDDFT approach. These searches were applied to the five polycyclic aromatic hydrocarbons (PAHs) shown in Fig.…”