Abstract
The dynamics of glass-forming systems shows a multitude of features that are absent innormal liquids, such as non-exponential relaxation and a strong temperature-dependence ofthe relaxation time. Connecting these dynamic properties to the microscopic structure of thesystem is challenging because of the presence of the structural disorder. Here we usecomputer simulations of a metallic glass-former to establish such a connection. By probingthe temperature and wave-vector dependence of the intermediate scattering function wefindthat the relaxation dynamics of the glassy melt is directly related to the local arrangement oficosahedral structures: Isolated icosahedra give rise to a liquid-like stretched exponentialrelaxation whereas clusters of icosahedra lead to a compressed exponential relaxation that isreminiscent to the one found in a solid. Our results show that in metallic glass-formers thesetwo types of relaxation processes can coexist and give rise to a dynamics that is surprisinglycomple