Entropy, glass-forming liquids structure

Our model [25,33,37 39,48] relies on a physical picture (see Fig. 1) that (i) there exist distinct locally favored structures in any liquids and (ii) such structures are formed in a sea of normal liquid structures and its number density increases upon cooling since they are energetically more favorable by A than normal liquid structures. The specific volume and the entropy are larger and smaller for the former than the latter, respectively, by Av and Act. We identify locally favored structures as a minimum structural unit (symmetry element). It is tetrahedral order for water-type liquids, whereas icosahedron for metallic glass formers [60]. To express such short-range bond ordering in liquids, we introduce the so-called bond-orientational order parameter Qim [64,65]. 

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