机器学习势能无法准确模拟玻璃态二氧化硅的中程有序结构。
Neutron and X-ray Diffraction Reveal the Limits of Long-Range Machine Learning Potentials for Medium-Range Order in Silica Glass
- 用长程注意力机制改进机器学习势能,仍无法还原真实玻璃结构。
- 两种模型均过度增强第一尖锐衍射峰,导致结构过于有序。
- 需更优数据与采样策略才能准确捕捉液-玻璃转变过程。
玻璃态二氧化硅是光学和电子学的基础材料,但准确预测其介观有序(MRO)仍是机器学习原子间势能(MLIPs)的重大挑战。尽管局部势能能良好再现短程的SiO4四面体网络,但仅靠局域性是否足以恢复第一尖锐衍射峰(FSDP)——MRO的主要实验特征尚不明确。本研究结合中子与X射线衍射测量,利用基于MACE的两类模型(短程SR与长程LR)进行大规模分子动力学模拟。结果表明:SR模型在液态和玻璃态下均产生过强的FSDP,造成过度有序;引入长程相互作用虽改善了液态结构的吻合度,但在淬火后仍无法恢复实验观测的非晶态MRO。环统计与键角分析显示,SR模型中六元环占比过高且分布过窄,而LR模型虽更宽但仍具偏差。二者均保持正确的四面体几何,但Si-O-Si键角变化受限,表明网络柔性不足。这些结构特征说明两类模型均保留了母液网络的过度记忆,导致玻璃化过程中形成动力学陷阱的非物理中程结构。结果表明,显式长程相互作用虽必要,却不足以实现对无序二氧化硅的精准建模,还需训练数据与采样策略充分反映液-玻璃转变过程。
原文摘要 · Abstract (English)
Glassy silica is a foundational material in optics and electronics, yet accurately predicting its medium-range order (MRO) remains a major challenge for machine-learning interatomic potentials (MLIPs). While local MLIPs reproduce the short-range SiO4 tetrahedral network well, it remains unclear whether locality alone is sufficient to recover the first sharp diffraction peak (FSDP), the principal experimental signature of MRO. Here, we combine neutron and X-ray diffraction measurements with large-scale molecular dynamics driven by two MACE-based models: a short-range (SR) potential and a long-range (LR) extension incorporating reciprocal-space gated attention. The SR model systematically over-structures the network, producing an overly intense FSDP in both the liquid and glassy states. Incorporating long-range interactions improves agreement with experiment for the liquid structure by reducing this excess ordering, but the LR model still fails to recover the experimental amorphous MRO after quenching. Ring-statistics and bond-angle analyses reveal that SR model exhibits an artificially narrow distribution dominated by six-membered rings, while the LR model produces a broader but still biased ring population. Despite preserving the correct tetrahedral geometry, both models show limited variability in Si-O-Si angles, indicating constrained network flexibility. These structural signatures demonstrate that both models retain excessive memory of the parent liquid network, leading to kinetically trapped and nonphysical medium-range configurations during vitrification. These results show that explicit long-range interactions are necessary but not sufficient for predictive modelling of disordered silica and suggest that accurate MRO further requires training data and sampling strategies that adequately represent the liquid-to-glass transition.
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