On the role of Icosahedral-like clusters in the solidification and the mechanical response of Cu-Zr metallic glasses by Molecular Dynamics simulations and Density Functional Theory computations

Cu-Zr Metallic glasses (MG) are considered to be composed of Icosahedral-like (ICO) clusters that may be distorted, truncated and/or interconnected. Aiming in gaining insight on the role of these units in the solidification-glass formation processes, as well as under mechanical solicitation, we performed detailed analysis of the electronic density of states, based on the Density Functional Theory, of the basic ICO-like clusters that were extracted from Cu65Zr35 equilibrium Molecular Dynamics (MD) configurations at various temperatures within the range from 2000 K to 300 K. In line with previous studies, we found that the d valence electrons of the Zr shell atoms occupy states close to the Fermi level, while s-s and d-s electronic hybridizations of the Cu-core/Cu-shell with the Cu shell atoms, respectively, occur at lower energy states and account for the deformation of the clusters, which is exclusively accomplished by these Cu-Cu distortions. Moreover, we found that upon quenching the mean atomic distances of the ICOs are decreasing due to shortening of the Cu-core/shell - Cu shell bonds, resulting in shifts of the corresponding states towards lower energies. Interestingly, it came out that the temperature dependence of these energies is linear, exhibiting slope changes at the melting and glass transition points. We applied the same analysis on ICOs extracted from Cu50Zr50 MD configurations under tensile solicitation from where we deduced the alterations that are caused in the electronic densities of states. These results could be of use for the understanding of the bonding characteristics of Cu-Zr model MGs and the mechanisms for the accommodation of the mechanical deformation.