Nonadiabatic Dynamics of the Molecular Tully Models with the Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory

In this study, we perform on-the-fly nonadiabatic molecular dynamics (NAMD) simulations for three molecular systems (ethylene, DMABN, and fulvene), which are suggested as molecular versions of the Tully models, with the trajectory surface hopping method based on the mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT). We employ several density functionals (CAM-B3LYP, M06-2X, BH&HLYP, and DTCAM-VAEE) in the MRSF-TDDFT calculations and compare the results with those obtained with the SA-CASSCF and MS-CASPT2 methods. For the ethylene molecule, the dynamics results obtained with MRSF-TDDFT compare very well with those obtained with MS-CASPT2, and the results with different functionals are similar. For the DMABN and fulvene molecules, the dynamics results with different functionals show certain differences, while the DTCAM-VAEE functional performs best among all functionals compared to MS-CASPT2. Moreover, for all molecules, MRSF-TDDFT outperforms SA-CASSCF for all functionals used in this work. We further explain the discrepancies of the dynamics results with different electronic structure methods through reaction pathway analysis. Overall, we strongly recommend the use of MRSF-TDDFT, especially with the DTCAM-VAEE functionals, in the NAMD simulations for complex molecular systems in the future, considering its good balance between accuracy and computational cost.