To investigate the performance of the parametrization approach with respect to particle densities, three different LHA models are considered, to take into account the effect of different compositions. The only difference in the input parameters of the VSOMM2 among the models was the random seed. The system's densities were calculated with the help of the GROMACS tool gmx energy. Because standard masses of Martini were used for the coarse-grained model, the densities were estimated with the time evolution of the system's volume, to enable a better comparison between the atomistic and coarse-grained systems. The time average of the densities was determined by dividing the total mass of the corresponding atomistic system by the time-averaged volume. Thus, an atomistic and a coarse-grained system with the same composition and the same volume would yield an equal density. In Figure , the densities of the atomistic systems, coarse-grained systems with tiny water, and coarse-grained systems with regular water are plotted against x water , which is the heavy atom fraction of water with respect to the whole system. For the atomistic systems, overall, the densities decreased with increasing water content. Changes in densities were less pronounced for the coarse-grained systems and relatively similar when the different compositions were compared. When comparing the densities of the atomistic and coarse-grained systems, some deviations were apparent and more pronounced in the case of lower water content. The largest discrepancies between the atomistic and coarsegrained systems were visible when using regular water, with a density deviation of around 11 %. This gap becomes reduced with increasing water content. For the water range considered, the coarse-grained systems with regular water came closest to the reference densities at the highest water content. In the case of tiny water, the densities approached atomistic density at a higher water content, achieving a good level of agreement, but slightly overestimating the density. The atomistic systems with low water content are assumed to be more rigid. To evaluate the relaxation process of a structure, the time evolutions of the densities were calculated. The densities needed longer to equilibrate for systems with a lower water content. In the case of the LHA1 model with x water = 0.228, the equilibration time had to be extended by 100 ns. This was done similarly for the LHA2 model with x water = 0.195 and x water = 0.225, whereby the equilibration time was extended by 400 ns. When comparisons were made between different compositions of the coarse-grained systems, the density curves had greater similarities. Presumably, due to the coarse-graining process, the finer details and characteristics of the different systems are averaged out, making the systems behave more similarly. Deviations between the atomistic and coarse-grained models are presumed to be caused by the inability of coarse-grained water to accurately fill in small voids, which are more prevalent with lower water contents. This could partially explain the smaller gap between the models with tiny water, although the overall density trend was not reproduced in this case. The tiny water model could also show a slight overestimation of the density when the water content was increased further. It is, however, expected that, when x water approaches 1, the densities will match as well as the coarse-grained water model reproduces the density of atomistic bulk water. Therefore, the highest deviations are presumed to be visible in the range of x water considered in this research, or when considering even drier SOM models. Models with higher water contents should be considered, for instance when the coarsegrained model is parametrized to reproduce the atomistic system's density. To achieve this, the non-bonded interactions could be adjusted, as they may have a significant influence on the overall density (see, for instance, Lutsyk et al. ). However, the strong heterogeneity of the SOM systems could make this kind of matching a challenging task. It could therefore be investigated in future research. Finally, it can be seen that the density of systems with higher water content was reproduced more accurately. It should also be noted that the systems with small and tiny water should be used with caution, as their transferability to different systems was not as extensively tested as for those with regular water . Therefore, for the remainder of this study, systems with regular water are further considered.