Upon cooling, the sizes of the clusters and strings increase, which may cause a higher temperature dependence of the structural relaxation at lower temperatures and, hence, the deviations from Arrhenius behavior. When the structural relaxation evolves, different groups of particles become highly mobile. In doing so, particles in the neighborhood of previously mobile particles have a higher tendency to become mobile than other particles, i.e., there is an enhanced probability for continuous mobility propagation.
When striving for a theoretical description of the glass transition, the temperature dependence of the structural relaxation is a crucial input. However, there is no consensus in the literature which functional form best describes the characteristic deviations from the Arrhenius law. Recently, it was proposed to decompose the activation energy into two contributions: a contribution, which is constant and is determined by the dynamics of the high-temperature liquid, and a contribution, which increases upon cooling and describes the growing cooperativity of the dynamics. Our simulations results for various models of glass-forming liquids, including water, silica melt, and ionic liquids, reveal that the glassy slowdown can be traced back to an exponential temperature dependence of the cooperative contribution to the activation energy. This finding yields an important target for the theoretical modelling.