Intermediate regime. To capture longer timescale events we do an extensive local minima energy structure search using minima hopping. We find the exchange rates connecting minima using a transition state search with the MLFF. For MFU-4l, a rotational flip of the hydroxyl group of the bicarbonate (Fig. ) is found which leads to the two carbonyls becoming chemically equivalent (see S15). We use the nudged elastic band method and find an energy barrier of 0.49 eV, which corresponds to a rate of 2.4 x 10 5 Hz under the harmonic approximation at room temperature (see S16). Using the calculated rate constant along with the static DFT carbonyl values (see Fig. ) as inputs to the stochastic hopping package EXPRESS, the two distinct carbonyl peaks coalesce, is a degree of sensitivity of the simulated peak shape to the precise value of the calculated rate constant (see Fig. ). Such sensitivity explains the discrepancy in the final carbonyl model, however, overall, the success of this modelling supports a specific two-component motion of carbonyl 'seesaw' and proton hopping in the CO 2 binding mode in MFU-4l (Fig. ). This reveals not only the detailed nature of CO 2 binding in MFU-4l but also provides insight that can be transferred to other similar metal-binding systems. The MLFF is highlighted as critical in keeping the computational cost affordable when modelling dynamics effects across all exchange regimes. Without the use of MLFF-MD, the nature of dynamics and exchange regime would be unknown; rate constant information would have to be assumed for stochastic hop modelling, and no refinement of the non-explicitly exchanging environments (e.g. hydroxyl peak) would be possible. Notably, this contrasts significantly to the 17 O NMR modelling of amine-based carbon capture materials, where static DFT modelling is sufficient. Thus, we demonstrate that the modelling of dynamics by MLFF methods is a key component for the assessment of hydroxide-based CO 2 capture materials. peaks clearly identifiable at 159 and 163 ppm. These are in agreement with the previously reported value of 159.6 ppm -only a single environment was previously assigned despite the apparent asymmetry of the chemisorbed CO 2 peak. Consistent chemisorbed CO 2 environments were reproduced for a range of samples (Figure ). These values fall in the expected range for bicarbonate and carbonate anions (161-168 ppm in solution, and 160-169 ppm 77 in solid-potassium crystals), but it is hard to make conclusive assignments with any confidence.