Icosahedral Order in Liquids

A research topic across the group’s papers.

Liquid and supercooled metals contain short-lived local motifs with five-fold symmetry, the most studied being the 13-atom icosahedron: a central atom and 12 neighbours. In simulations these are usually detected by Voronoi tessellation, where an atom with Voronoi index <0,0,12,0> sits at the centre of a perfect icosahedron. Icosahedra can share atoms with one another (vertex, edge, face or intercross sharing) to form larger medium-range clusters. Growth of icosahedral order on cooling has been linked to dynamic slowdown, glass formation and breakdown of the Stokes–Einstein relation.

Clustering shared-atom icosahedra in liquid Al–Si (2022)

Zhan and Kitchin defined clusters by shared atoms rather than by shared bonds, building a binary neighbour matrix for icosahedral atoms and their neighbours and applying single-linkage agglomerative clustering from scikit-learn, then tracking clusters over time when at least 13 atoms persisted between frames. In Al0.90Si0.10 and Al0.94Si0.06 the number of clustered atoms, the largest cluster size (about 40 atoms) and the fraction of clusters lasting over 1 ps all grew on cooling toward crystallization, with lifetimes up to 8 ps. Using per-atom transport estimates, they found these clusters raise viscosity without changing diffusion (Zhan 2021). Summary: zhan2022b.

Papers on this topic