To improve phase space overlap, we introduced more intermediate states along the path for removing the restraints (see . We chose to break down the simulation in smaller parts, adding a significant amount of states near the point where the harmonic restraints are approximately zero. The MBAR estimate of ∆A I E M →solid for fcc argon is -1016.0(2) k B T using 300 states. TI's corresponding value was -1017(1) k B T, differing by far from the (incorrect) value of -1666.5(8) k B T obtained above with fewer states. Phase space overlap diagrams showed significant improvement in the configuration overlap between the states (Supporting Information). Thus, increasing the number of states was an effective strategy, and we used it in all subsequent calculations.