Nonadiabatic molecular dynamics simulation for the ultrafast photoisomerization of dMe-OMe-NAIP based on TDDFT on-the-fly potential energy surfaces

Nonadiabatic molecular dynamics simulations for ultrafast photo-induced ring-opening and isomerization reactions of 2,2-diphenyl-2H-chromene

Nonadiabatic molecular dynamics simulations with a global switching algorithm have been performed at the TD-CAM-B3LYP-D3/def2-SVP level of theory for ultrafast photo-induced ring-opening and isomerization reactions upon S1 excitation for 2,2-diphenyl-2H-chromene (DPC). Both DPC-T and DPC-C conformers undergo ring-opening relaxation and isomerization pathways accompanied with pyran conformation conserved and converted on the S1 or S0 states via competition and cooperation between C-O bond dissociation and pyran inversion motions. Upon S1 excitation, the DPC-T mainly relaxes to the T-type conical intersection region and thus yields a higher ring-opening efficiency with a faster S1 decay and intermediate formation than those of the DPC-C mainly relaxing to C-type conical intersection. The simulated ring-opening quantum yield for DPC-T (DPC-C) is 0.91 (0.76), which is in good agreement with the experimental value of 0.7-0.9, and the thermal weight averaged lifetimes are estimated as 182.0 fs, 228.6 fs, and 1262.4 fs for the excited-state decay, intermediate formation, and ring-opening product, respectively. These time constants are in good agreement with the experimentally measured τ1 time constant of 190-450 fs and τ2 time constant of 1000-1800 fs. The present work could be a valuable reference for understanding the nature of the photorelaxation mechanisms of DPC, and could help to develop DPC-based photoresponsive materials.

Analytic Gradient for Time-Dependent Density Functional Theory Combined with the Fragment Molecular Orbital Method

The analytic energy gradient of energy with respect to nuclear coordinates is derived for the fragment molecular orbital (FMO) method combined with time-dependent density functional theory (TDDFT). The response terms arising from the use of a polarizable embedding are derived. The obtained analytic FMO-TDDFT gradient is shown to be accurate in comparison to both numerical FMO-TDDFT and unfragmented TDDFT gradients, at the level of two- and three-body expansions. The gradients are used for geometry optimizations, molecular dynamics, vibrational calculations, and simulations of IR and Raman spectra of excited states. The developed method is used to optimize the geometry of the ground and excited electronic states of the photoactive yellow protein (PDB: 2PHY).

Trajectory surface hopping molecular dynamics simulations for retinal protonated Schiff-base photoisomerization

Global switching trajectory surface hopping molecular dynamics simulations are performed using accurate on-the-fly (TD)CAM-B3LYP/6-31G potential energy surfaces to study retinal protonated Schiff-base photoisomerization up to S₁ excitation. The simulations detected two-layer conical intersection networks: one is at an energy as high as 8 eV and the other is in the energy range around 3-4 eV. Six conical intersections within the low-layer energy region that correspond to active conical intersections under experimental conditions are found via the use of pairwise isomers, within which nonadiabatic molecular dynamics simulations are performed. Eight isomer products are populated with simulated sampling trajectories from which the simulated quantum yield in the gas phase is estimated to be 0.11 (0.08) moving from the all-trans isomer to the 11-cis (11-cis to all-trans) isomer in comparison with an experimental value of 0.09 (0.2) in the solution phase. Each conical intersection is related to one specific twist angle accompanying a related CC double bond motion during photoisomerization. Nonplanar distortion of the entire dynamic process has a significant role in the formation of the relevant photoisomerization products. The present simulation indicates that all hopping points show well-behaved potential energy surface topology, as calculated via the conventional TDDFT method, at conical intersections between S₁ and S₀ states. Therefore, the present nonadiabatic dynamics simulations with the TDDFT method are very encouraging for simulating various large systems related to retinal Schiff-base photoisomerization in the real world.