Space-time rigidity and viscoelasticity of glass forming liquids: The case of chalcogenides

The viscoelasticity of glass-forming fluids contains sustantial information about space-time rigidity. Viscoelasticity and rheology provide alternative experimental, computational and theoretical ways to asses chemical composition effects in the relaxation of supercooled liquids near the glass transition. In particular, the transverse current correlation and transversal dynamical structure factor contain space-time information allowing to relate the dynamical gap of transversal vibrational modes with floppy modes and relaxation times in the liquid. Here, a short revision is made of the subject, including simulations of Tellurium, a typical chalcogenide glass. Our results are similar to those obtained for typical metallic liquids. To rationalize this result, an statistical mechanics analysis in the strain ensemble is performed by using a model that incorporates flexibility and hard-core potentials. This shows that the entropy is akin to a hard-cord fluid as angular bonds only renormalize the entropy if they are not substantially affected by temperature effects. Finally, a comparison is made with Selenium, where bond breaking effects do not allow such a straight-forward treatment.