A key aspect of our simulated dynamics is that it unfold in full dimension, thus allowing us to analyse nuclear motion along all 183 modes of [Fe(bmip) 2 ] 2+ . Figure shows the mode activity of nuclear motion for the case of 400 nm excitation, calculated as standard deviation of nuclear displacements projected onto dimensionless mass-frequency weighted normal mode coordinates, see ESI. As is clear from Figure , nuclear motion during the excited-state dynamics of [Fe(bmip) 2 ] 2+ is dominated by 5 modes: ν 14 (as anticipated, the most dominant one, i.e., we chose this breathing mode to visualize the PESs in Figure ), ν 16 , ν 18 , ν 35 , and ν 36 , which are all identified to possess Fe-N/Fe-C stretching characters; we note that this result is very similar for the case of 485 nm excitation, see ESI, Figure . Among these 5 modes, 4 are identical to those used in our previous QD simulations (instead of the fifth mode ν 35 , we used mode ν 34 , which appears here with smaller mode activity), supporting that we indeed chose the most dominant modes. However, the population dynamics obtained with QD based on these modes is very different from our present full-D TSH results, in particular regarding the appearance of the ∼200-300 fs 3 MC component. Our interpretation for this discrepancy is as follows: all identified dominant Fe-N/Fe-C stretching modes are activated and operative in the 3 MC states, due to occupation of an antibonding e * g orbital, but for the 3 MLCT → 3 MC transition, nuclear motion in the 3 MLCT states is in fact decisive.