Structural transformations of crystalline solids and other condensed-matter systems underlie a broad class of technologically signi”cant problems. A fundamental atomic-scale understanding is required to determine the onsets of such structural transitions, i.e., the conditions under which materials undergo transitions as a result of thermal, mechanical, or chemical driving forces. Accurate theoretical prediction of such structural transition onsets is a major challenge that lies at the heart of condensed-matter physics, materials science, and the entire spectrum of engineering sciences. Toward this end, atomistic simulation methods provide ideal means for mechanistic analysis and quantitative prediction.