Size-dependent melting of onion-like fullerenic carbons: a molecular dynamics and machine learning study

R Fu and YH Xu and S Qiao and YS Liu and YW Lin and Y Li and ZS Zhang and JY Wu, JOURNAL OF PHYSICS-CONDENSED MATTER, 34, 425402 (2022).

DOI: 10.1088/1361-648X/ac877e

The melting thermodynamic characteristics of 2- to 20-layered onion-like fullerenes (OLF (n) ) (C-60@C-240 to C-60@center dot center dot center dot@C-6000 center dot center dot center dot@C-24000) are comprehensively explored using first-principles-based ReaxFF atomistic simulations and random forest machine learning (RF ML). It is revealed that OLF (n) shows lower thermal stability than the counterparts of single-walled fullerenes (SWF (n) ). The melting point of SWF (n) increases monotonically with increasing size, whereas for OLF (n) , an unusual size-dependent melting point is observed; OLF (n) with intermediate size shows the highest melting point. For small OLF (n) , the melting occurs from the inner to the outer, whereas for large OLF (n) , it nucleates from the inner to the outer and to intermediate fullerenes. The melting and erosion behaviors of both SWF (n) and OLF (n) are mainly characterized by the nucleation of non-hexagons, nanovoids, carbon chains and emission of C-2. RF ML model is developed to predict the melting points of both SWF (n) and OLF (n) . Moreover, the analysis of the feature importance reveals that the Stone-Wales transformation is a critical pathway in the melting of SWF (n) and OLF (n) . This study provides new insights and perspectives into the thermodynamics and pyrolysis chemistry of fullerenic carbons, and also may shed some lights onto the understanding of thermally-induced erosion of carbon-based resources and spacecraft materials.

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