This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In the physical sense, glass is not limited to familiar window glass; it forms whenever a liquid is cooled so quickly that it cannot crystallize. As a result, glass has an amorphous structure—that is, its "building blocks" are not arranged regularly as in crystals.
At the same time, however, glass is as resistant to deformation as a crystalline solid. Exactly what glass is remains one of the major unsolved questions in condensed-matter physics. For example, it is unclear whether the transition from liquid to the glassy state is a genuine thermodynamic phase transition between two distinct states of matter or a purely dynamical phenomenon in which the liquid merely deforms extremely slowly.
A hypothetical fourth state of matter—alongside gas, liquid and crystalline solid—has been predicted by several theoretical approaches and is referred to as the "ideal glass." Experimental or numerical confirmation has not been possible so far, however, because obtaining an ideal glass would require cooling the corresponding liquid infinitely slowly without crystallizing. A team of physicists led by Gerhard Jung from the Department of Theoretical Physics has now succeeded in computationally modeling the cooling of a two-dimensional liquid in such a way that it reaches the ideal glass state. Their research is published in the Proceedings of the National Academy of Sciences.
The key was the combination of different numerical methods because conventional computer simulations hit a hard limit for this task: They calculate how particles move step by step under the influence of the forces acting on them. Calculations of this kind can represent only a limited time span, even if repeated millions of times. Only the integration of three different statistical methods enabled the research team to cool a model system all the way down to absolute zero.
"We show that it is fundamentally possible to model ideal glasses and to test theories of the glass transition. That was not clear before and is therefore extremely positive news," Jung said. With the help of the simulation, the researchers were able to investigate the properties of an ideal glass directly for the first time.
They observed that the number of possible particle configurations becomes extremely small at low temperatures. This is unusual for amorphous structures, which are typically characterized by countless different, equivalent configurations—unlike a crystal, which has one clearly prescribed structure. In the ideal glass, however, this diversity shrinks almost completely.
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