Reconsidering the non-bonded interactions, as mentioned previously, the bead types for the ions and charged groups are mostly fixed for the Martini force field. For the SOM models, the calcium ions were represented by SD beads and the negatively charged carboxylate groups by SQ5n beads. These are the respective types of standard bead types. The aim was to investigate how these parametrizations of ions reproduce properties of the reference. This was done by calculating the radial distribution functions (RDFs) between the carboxylate groups and calcium ions, which are shown in Figure . In this case, the SOM models with the lowest and highest water content were considered. The RDFs from the mapped trajectories (blue) show a peak at around 0.26 nm, which is more pronounced for the system with low water content. For the mapped system with high water content, a second broader peak is visible around 0.5 nm. The coarse-grained RDFs (orange) are similar for both cases, showing a peak at around 0.45 nm. However, a slightly better agreement between the mapped and coarse-grained RDF was observed for the case with high water concentration. Any peaks which are lower than 0.40 nm, are not captured by the coarse-grained model. The form of the RDFs is mainly determined by the potential, describing the interaction between both groups. In the present case, the coarse-grained potential is a combination of a Lennard-Jones and a Coulomb potential. Therefore, it is inherently not possible to reproduce a double peak as in the case with high water content. The peaks at lower distances cannot be captured by the coarse-grained model, due to the predefined particle size of the beads. In general, to accurately reproduce RDF curves, it would be necessary to apply tabulated potentials, describing the non-bonded interactions. One possible method, that involves conducting such matching, is the so-called Iterative Boltzmann Inversion 65 . However, applying this method is beyond the scope of this study. The position of the mapped RDF in the high water case was partially reproduced by the coarsegrained RDF's first peak. Concerning this, it could again be argued that the model captures the features of the reference at higher water content more effectively, similarly to the system density. It can also be seen that the coarse-grained RDF is less affected by the water content as the reference. This might be an indication of the coarse-grained model's limited transferability, regarding different water concentrations in the system. To better understand the form of the mapped RDFs, angle distributions of the calcium ions and oxygen atoms of carboxylate groups were calculated. The atomistic systems with the lowest and highest water content were again considered. The results of the angle calculations are shown as distributions in Figure . Most notably, three peaks can be identified, which have been labeled as peak I, II, and II respectively. These peaks are roughly visible in the range from 0 • to 20 • , from 20 • to 30 • and from 40 • to 55 • , respectively. Additionally, the center of geometry distances between the calcium ions and carboxylate groups were calculated (see Figure ), and associated with each of the three peaks from the angle distributions. For instance, for configurations of calcium ions and carboxylate groups associated with peak III, the center of geometry distances were calculated for those configurations with an angle between 40 • and 55 • and plotted for both water contents. This was also done with the configurations corresponding to the other two peaks, using the corresponding angle ranges. This resulted in a total of six different curves. From the angle distributions, it can be ascertained that the configurations associated with peak III are more often observed in the case of lower water content. This also holds for peak I configurations, but the difference to the system with the lower water content is less pronounced. In contrast, peak II configurations are more pronounced in the system with the higher water content. Peak III configurations can be associated with lower distances, visible in the peaks at around 0.26 nm. The calcium ions are very close to the oxygen atoms of the carboxylate group, which results in a configuration that is assumed to be highly stable. Galicia-Andrés et al. investigated the role of metal cations on the stability of SOM with atomistic simulations. From the results, the authors concluded that cations such as calcium Different peaks can be assigned to specific complexes, which are inner-sphere complexes (monodentate (M) and bidentate (B)) and outersphere complexes (OSC). Please note that, to achieve a better representation, the curves for x water = 0.425 are shifted by a count of 200. ions are important for the SOM agglomeration process. Due to the presence of calcium ions, more dense SOM phases are created, which increases the overall stability of the SOM system. Comparing further the results to the work of Galicia-Andrés et al. , monodentate (M) inner sphere complex and a bidentate (B) inner sphere complex were investigated there.