Npj Comput. Mater.:大尺度、第一性原理精度的激光过程:机器学习——分子动力学模拟
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来自国防科技大学理学院的戴佳钰教授团队,提出了一种高效、准确的激发态分子动力学模拟框架——TTM-DPMD,构建显式依赖电子分布的神经网络激发态势能面,并与双温模型分子动力学深度耦合,可以内禀描述电子激发导致的非热效应和非绝热能量交换等,并将模拟规模拓展到百万原子量级。
FIG 1 Schematic diagram of workflow for efficient and accurate simulation of laser-driven atomistic dynamics.
该研究以30 nm厚度的多晶钨薄膜为对象,实现了样品在厚度维度的全尺度模拟(包含75万原子),观察到:
1) 即使在低激光通量下(激光能量密度为0.08 MJ/kg,对应电子温度约为5000 K),激光产生的热电子也足以诱导声子软化,显著改变电子衍射峰下降动力学,从而获得与实验定量一致的结果。
FIG 2 capturing nonthermal effect with TTM-DPMD approach
2)在高激光能量密度下(激光能量密度为0.80 MJ/kg,对应电子温度约为11000 K),热电子会额外贡献高达10 GPa的非热应力,在薄膜表面驱动剧烈的单轴膨胀过程,使得系统的热力学、微观结构演化表现出强烈的非均匀性,与传统热过程截然不同,必须依赖于大尺度、激发态的双重描述。
FIG 3 Hot electron modifies the thermodynamic pathway and introduce significant inhomogeneity in thermodynamic profile and structural evolution
该研究为理解激光与物质相互作用过程的原子尺度动力学提供了可靠的研究手段,并指出在大尺度下,热电子驱动的非热行为会产生截然不同的热力学路径和结构演化。该文近期发表于npj Computational Materials 9:213 (2023),英文标题与摘要如下,点击左下角“阅读原文”可以自由获取论文PDF。
Full-scale ab initio simulations of laser-driven atomistic dynamics
Qiyu Zeng, Bo Chen, Shen Zhang, Dongdong Kang, Han Wang, Xiaoxiang Yu & Jiayu Dai
The coupling of excited states and ionic dynamics is the basic and challenging point for the materials response at extreme conditions. In the laboratory, the intense laser produces transient nature and complexity with highly nonequilibrium states, making it extremely difficult and interesting for both experimental measurements and theoretical methods. With the inclusion of laser-excited states, we extend an ab initio method into the direct simulations of whole laser-driven microscopic dynamics from solid to liquid. We construct the framework of combining the electron-temperature-dependent deep neural-network potential energy surface with a hybrid atomistic-continuum approach, controlling non-adiabatic energy exchange and atomistic dynamics, which enables consistent interpretation of experimental data. By large-scale ab initio simulations, we demonstrate that the nonthermal effects introduced by hot electrons play a dominant role in modulating the lattice dynamics, thermodynamic pathway, and structural transformation. We highlight that the present work provides a path to realistic computational studies of laser-driven processes, thus bridging the gap between experiments and simulations.
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