Figure shows the variation in concentration over simulation time for both fragments. In each case, after an appropriate equilibration period, the concentration fluctuates around the target value, demonstrating that not only can GCNCMC simulations maintain a defined concentration but also rapidly equilibrate the system. The final mean concentration for acetone was 0.55 ± 0.02 M and 0.56 ± 0.02 M when starting from 0 M and 1 M respectively. While slightly higher than the desired concentration of 0.5 M, the consistency between the two systems is reassuring and indicates that the values of the excess chemical potential of either the ligand or water may not be sufficiently accurate to sample 0.5 M exactly. In the case of pyrimidine, a lower concentration of 0.1 M was selected and well reproduced. Further discussion of these results is available in the Supplementary Information.