The weight function is a decreasing function of the potential energy above the minimum, and has the effect of prioritizing the objective function towards low-energy structures that are statistically most probable during the MD simulations. For relative energies below D, the weight takes a constant value, then becomes inversely proportional to energy until the upper cutoff U is reached, where the weight drops to zero. The lower cutoff D is set to 5 kcal/mol in both AMBER-FB15 and this work. However, in contrast to the canonical amino acids where U is set to 20 kcal/mol, the dianionic residues have a substantial number of structures with relative energies greater than 20 kcal/mol (shown in the Supporting Information). Therefore, the cutoff energy was increased from U = 20 kcal/mol to U = 40 kcal/mol for the dianionic species. The A(y