A necessary condition for well-defined structural minima that are likely to have good folding properties is that there exist well-defined clusters with high structural similarity that are structurally distant from other clusters. We calculate and report the average RMSD within all cluster structures to their identified minimum energy structures (RM SD cluster ), to measure how tightly defined the clusters are. We also calculate RMSD between cluster minimum-energy structures (RM SD inter ) to quantify how structurally different clusters are from one another. With RM SD cluster and RM SD inter , we can asses how structurally distinct clusters are from one another and how how tightly spread clusters are about their medoids.