Simulation of Ultrafast Excited-State Dynamics in Fe(II) Complexes: Assessment of Electronic Structure Descriptions

The
assessment of
electronic structure descriptions utilized
in
the simulation of the ultrafast excited-state dynamics of Fe(II) complexes
is presented. Herein, we evaluate the performance of the RPBE, OPBE,
BLYP, B3LYP, B3LYP*, PBE0, TPSSh, CAM-B3LYP, and LC-BLYP (time-dependent)
density functional theory (DFT/TD-DFT) methods in full-dimensional
trajectory surface hopping (TSH) simulations carried out on linear
vibronic coupling (LVC) potentials. We exploit the existence of time-resolved
X-ray emission spectroscopy (XES) data for the [Fe(bmip)2]2+ and [Fe(terpy)2]2+ prototypes
for dynamics between metal-to-ligand charge-transfer (MLCT) and metal-centered
(MC) states, which serve as a reference to benchmark the calculations
(bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, terpy = 2,2′:6′,2″-terpyridine).
The results show that the simulated ultrafast population dynamics
between MLCT and MC states with various spin multiplicities (singlet,
triplet, and quintet) highly depend on the utilized DFT/TD-DFT method,
with the percentage of exact (Hartree–Fock) exchange being
the governing factor. Importantly, B3LYP* and TPSSh are the only DFT/TD-DFT
methods with satisfactory performance, best reproducing the experimentally
resolved dynamics for both complexes, signaling an optimal balance
in the description of MLCT–MC energetics. This work demonstrates
the power of combining TSH/LVC dynamics simulations with time-resolved
experimental reference data to benchmark full-dimensional potential
energy surfaces.