The final assembled form of the NPs is shown in Fig. (also see Fig. ). These simulations required ~15,500 CPU hours on AMD EPYC 7742 processors. A similar string-like phase was also obtained in simulations using the many-body potential, but at the computational cost of only ~5 CPU hours on similar processors (Fig. ). In contrast, simulations using the two-body potential falsely predicted the formation of NP aggregates (Fig. ). For more quantitative comparison, we computed the time-averaged Steinhardt's bond orientational order parameters for each NP in the assembled structures. As shown in Fig. , the string-like structures assembled from both the CG force field and the many-body potential exhibit high 𝑞 E and 𝑞 F values that roughly spread over the same region in the 𝑞 E -𝑞 F plot, confirming that both interaction models produced similar assembly morphologies. In contrast, the order parameters of the NP aggregates predicted by the two-body potential are in the low 𝑞 E and 𝑞 F region and are well separated from those of the string-like phase. Lastly, given the enormous saving in computational cost afforded by our many-body potential, we were able to access NP assembly at even larger length and time scales. 2D Sheet Phase. Our success with assembling NP strings with the many-body potential prompted us to explore its ability to assemble 2D NP sheets-another structural phase formed by polymer-grafted NPs due to many-body effects. Based on our earlier discussion on cluster morphologies (Fig. ), 2D clusters are expected to form at intermediate strengths of three-body repulsion-when this repulsion is weak enough to allow the formation of 2D clusters but strong enough to destabilize the formation of 3D clusters. Therefore, we sought to develop a many-body potential for polymer-grafted NPs at a lower grafting density of 0.15 chains/𝜎 ! to target the 2D sheet phase. The training data were generated in the same way as described earlier for the densely grafted NPs (Fig. ). Their fitting procedure using PIPs was also similar, except that a 6 th -order PIP was found to be sufficient to fit the two-body PMF. The corresponding fitting parameters are listed in Tables and, and the parity plots for the two-and three-body contributions are shown in Fig. and.