John Russo
(Sapienza Università di Roma)

The thermodynamic fate of any glassy material is devitrification, a process that compromises their structural integrity and limits their functionality. However, recent experimental advances have enabled the preparation of ultrastable glasses, which exhibit exceptional thermodynamic and kinetic stability, making them indispensable for applications in pharmaceuticals, optical media, and cryogenic solutions. In this work, we present two numerical strategies to prepare and investigate ultrastable glasses.
The first approach involves suppressing volume fraction inhomogeneities by modifying the size distribution of particles ^[1]. Using this method, we demonstrate that devitrification can be effectively avoided, establishing a direct link between mechanical stability and a simple structural property—the distribution of local volume fractions. This insight provides a predictive framework for assessing glass stability and reveals a structural mechanism underlying avalanche devitrification.
The second approach employs molecular dynamics simulations of vapor deposition, showing that ultrastable glasses achieve enhanced stability through the formation of locally favored structures (LFS). By examining various glass-forming models, from binary mixtures ^[2] to strong glasses with directional bonding ^[3], we uncover the kinetic pathways that facilitate the formation of crystalline nuclei just below the surface. Together, these methods offer complementary perspectives on the design and stability of ultrastable glasses.

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