  Transition metal complexes for photochemical applications often feature a
high density of electron-vibrational states characterized by nonadiabatic and
spin-orbit couplings. Overall, the dynamics after photoexcitation is shaped by
rapid transitions between states of different character and multiplicity. Even
though transient absorption experiments enable characterization in terms of
kinetic rates, the complexity of the systems usually prevents a more detailed
analysis. Quantum dynamics simulations using quantum chemically determined
model Hamiltonians may provide such details. In particular, one is tempted to
pursue a model reduction, such as to identify couplings or vibrational modes
most relevant for the dynamics. Here, we address how such an endeavor is
challenged by the particular nature of transition metal complexes. For that
purpose, we performed quantum dynamics simulations for a recently studied
iron(II) homoleptic complex.
