Internal Conversion between Bright (1<sup>1</sup><i>B</i><sub><i>u</i></sub><sup>+</sup>) and Dark (2<sup>1</sup><i>A</i><sub><i>g</i></sub><sup>–</sup>) States in s-<i>trans</i>-Butadiene and s-<i>trans</i>-Hexatriene
Woojin Park, Jun Shen, Seunghoon Lee, Piotr Piecuch, Michael Filatov, Cheol Ho Choi
Abstract
potentials obtained with some multireference approaches, such as CASSCF and MRCIS(D), as well as with the linear-response formulation of time-dependent DFT (TDDFT), do not cross. Hence, caution needs to be exercised when studying the low-lying singlet excited states of polyenes with conventional multiconfigurational methods and TDDFT. The multistate many-body perturbation theory methods, such as XMCQDPT2, do correctly reproduce the curve crossing. Among the simplest and least expensive computational methodologies, the DFT approaches that incorporate the contributions of doubly excited configurations, abbreviated as MRSF (mixed reference spin-flip) TDDFT and SSR(4,4), accurately reproduce our best EOMCC results. This is highly promising for nonadiabatic molecular dynamics simulations in larger systems.