Multiple-State Nonadiabatic Dynamics Simulation of Photoisomerization of Acetylacetone with the Direct ab Initio QTMF Approach

In the present work, the quantum trajectory mean-field (QTMF) approach is numerically implemented by ab initio calculation at the level of the complete active space self-consistent field, which is used to simulate photoisomerization of acetylacetone at similar to 265 nm. The simulated results shed light on the possible nonadiabatic pathways from the S-2 state and mechanism of the photoisomerization. The in-plane proton transfer and the subsequent S-2 -> S-1 transition through the E-S-2/S-1-1 intersection region is the predominant route to the S-1 state. Meanwhile, rotational isomerization occurs in the S-2 state, which is followed by internal conversion to the S-1 state in the vicinity of the E-S-2/S-1-2 conical intersection. As a minor pathway, the direct S-2 -> S-1 -> S-0 transition can take place via the E-S-2/S-1/S-0 three-state intersection region. The rotamerization in the S-1 state was determined to be the key step for formation of nonchelated enolic isomers. The final formation yield is predicted to be 0.57 within the simulated period. The time constant for the S-2 proton transfer was experimentally inferred to be similar to 70.0 fs in the gas phase and similar to 50.0 fs in dioxane, acetonitrile, and n-hexane, which is well-reproduced by the present QTMF simulation. The S-1 lifetime of 2.11 ps simulated here is in excellent agreement with the experimentally inferred values of 2.12, 2.13, and 2.25 ps in n-hexane, acetonitrile, and dioxane, respectively. The present study provides clear evidence that a direct ab initio QTMF approach is a reliable tool for simulating multiple-state nonadiabatic dynamics processes.