First-Order-Like Liquid-to-Amorphous Transition in Boron: The Role of Geometrically Frustrated Icosahedral Ordering

Using ab initio molecular dynamics simulations combined with stepwise cooling, we uncover an abrupt structural transformation in deeply supercooled elemental boron between 2000 and 1900 K. Unlike previous investigations focused mainly on equilibrated liquid states, the present simulations resolve the atomic-scale pathway connecting the supercooled liquid to the resulting amorphous phase. The transformation is characterized by four concurrent discontinuous signatures: an ∼8% volume collapse, a cohesive energy release of ∼0.4 eV/atom, an increase in coordination number from 5.3 to 6.0, and rapid dynamical arrest. Structurally, the transition is marked by a pronounced decoupling between local and global order. The resulting amorphous phase exhibits short- and intermediate-range correlations similar to β-rhombohedral boron, while the global orientational order remains strongly suppressed (Q 6 ≈ 0.01), indicating the absence of developing long-range crystalline coherence. Instead, we identify a first-order-like liquid-to-amorphous transformation driven by geometric frustration. The cooperative emergence of five-fold symmetric B 12 motifs promotes local structural ordering and densification, while simultaneously limiting the formation of translational periodicity. These results provide atomistic insight into how local geometric preferences and frustration govern abrupt structural transformations in amorphous-forming systems.