The melting thermodynamic characteristics of 2- to 20-layered onion-like fullerenes (OLF _n ) (C₆₀@C₂₄₀ to C₆₀@···@C₆₀₀₀···@C₂₄₀₀₀) 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 C₂. 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.

中文翻译：

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洋葱状富勒烯碳的尺寸依赖性熔化：分子动力学和机器学习研究

2 至 20 层洋葱状富勒烯 (OLF) 的熔化热力学特性 _n ) (C ₆₀ @C ₂₄₀至 C ₆₀ @···@C ₆₀₀₀ ···@C ₂₄₀₀₀ ) 使用基于第一性原理的 ReaxFF 原子模拟和随机森林机器学习 (RF ML) 进行全面探索。据透露，OLF _n 显示出比单壁富勒烯（SWF _n ). SWF的熔点 _n 随着尺寸的增加单调增加，而对于 OLF _n ，观察到不寻常的尺寸依赖性熔点；奥林匹克 _n 具有中间尺寸的显示出最高的熔点。对于小OLF _n ，熔化从内到外发生，而对于大的 OLF _n ，它从内部到外部成核，再到中间富勒烯。SWF 的熔化和侵蚀行为 _n 和OLF _{n 主要特征在于非六边形、纳米空隙、碳链的成核和C 2}的发射。开发 RF ML 模型以预测两种 SWF 的熔点 _n 和OLF _n . 此外，对特征重要性的分析表明，Stone-Wales 变换是 SWF 熔化的关键途径 _n 和OLF _n . 这项研究为富勒碳的热力学和热解化学提供了新的见解和观点，也可能为理解热诱导的碳基资源和航天器材料侵蚀提供一些启示。