Fragility, Stokes–Einstein violation, and correlated local excitations in a coarse-grained model of an ionic liquid

摘要: Dynamics of a coarse-grained model for the room-temperature ionic liquid, 1-ethyl-3-methylimidazolium hexafluorophosphate, couched in united-atom site representation are studied via molecular dynamics simulations. The dynamically heterogeneous behavior resembles that fragile supercooled liquids. At or close to room temperature, liquid exhibits slow dynamics, characterized by nonexponential structural relaxation and subdiffusive behavior. time, closely related viscosity, shows super-Arrhenius Local excitations, defined as displacement an ion exceeding threshold distance, found be mainly responsible alternating structure cations anions. As temperature is lowered, excitations become progressively more correlated. This results decoupling exchange persistence times, reflecting violation Stokes-Einstein relation.