A Theory of Localized Excitations in Supercooled Liquids

The dynamics of glass-forming liquids dramatically slow down with decreasing temperature and are accompanied by dynamical heterogeneity. These phenomena can be understood from a structure-based perspective, where the relaxation behavior originates from the static properties, or a dynamics-based perspective, e.g., dynamical facilitation (DF) theory, where localized excitations, whose origin is assumed to be independent of structure, drive glassy dynamics by facilitating the relaxation of nearby excitations. Our work [1] shows that excitations are connected to the liquid inherent structure and elasticity by constructing a theory where excitations are localized pure-shear events, induced by T1 transitions that re-organize the first solvation shell. The theory predicts that the energy barrier to form excitations is a function of the inherent shear modulus and radial distribution function. The predicted energy barrier is compared to that of DF theory, where quantitative agreement is found across six models of poly-disperse glass formers. These results demonstrate a strong connection between the two competing perspectives of glassy dynamics. 

[1] M.R. Hasyim, K.K. Mandadapu, J. Chem. Phys. 155 (4), 44504, (2021)