基于第一性原理与深度神经网络势能建模的电子激发α-SiO₂中超快非热晶格失稳与极性光学散射抑制
Ultrafast Nonthermal Lattice Destabilization and Suppression of Polar Optical Scattering in Electronically Excited $α$-SiO$_2$ from First-Principles and Deep Neural Network Potential Modeling
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中文总结 AI 辅助
该研究采用第一性原理与深度神经网络势能结合的多尺度方法，揭示电子激发α-SiO₂随温度升高发生晶格失稳、极性光学散射抑制及原子流体相形成的超快动力学行为。
中文摘要 AI 辅助
我们提出了一种多尺度第一性原理到机器学习的方法，用于研究电子激发α-SiO₂中的超快晶格动力学。基于电子温度相关密度泛函理论（DFT）的从头算分子动力学（AIMD）被用来训练电子温度相关深度神经网络势能（DNNPs）。DNNPs的使用使得能够以接近DFT的精度对包含数千个原子的大尺寸α-SiO₂晶胞进行原子级建模。特别地，DNNPs让我们能够获得由电子温度突增激发的α-SiO₂的准确声子能带结构和分子动力学（MD）。随着电子温度Te的升高，发现α-SiO₂发生显著的晶格失稳，这表现为弹性稳定性准则被违反、体积大幅膨胀、体模量急剧降低，以及由于反键态占据导致Si-O键逐渐弱化。从电子和声子能带结构中，我们估算了Frohlich耦合常数，其随Te升高而减小，表明在较高电子温度下α-SiO₂会发生向非极性相的转变，这一结论得到了Bader电荷分析的佐证。我们还提出，当Te>2 eV时，极性光学声子散射应被强烈抑制。通过大尺寸晶胞的DNNP-MD模拟，我们发现，在最初的几百飞秒内无法达到由麦克斯韦-玻尔兹曼分布定义的明确定义的热平衡，这种行为解释了Te突增后动力学温度的非单调平衡过程。当Te升高至2.6 eV后，Si和O原子首先在两个不同温度下分别达到平衡，表明形成了原子流体相，这与近期的实验和理论结果一致。
英文摘要
We present a multiscale first-principles-to-machine-learning approach to investigate ultrafast lattice dynamics in electronically excited $α$-SiO$_2$. Ab initio molecular dynamics (AIMD) based on electronic-temperature-dependent density functional theory (DFT) are used to train electronic-temperature-dependent deep neural network potentials (DNNPs). The use of DNNPs enables atomistic modeling at near-DFT accuracy of large $α$-SiO$_2$ cells with thousands of atoms. In particular, DNNPs allowed us to obtain accurate phonon band structures and molecular dynamics (MD) of $α$-SiO$_2$ excited by a sudden increase in electronic temperature. With increasing electronic temperature, $T_e$, pronounced lattice destabilization of $α$-SiO$_2$ is found, as evidenced by violations of elastic stability criteria, substantial volumetric expansion, a sharp reduction of the bulk modulus, and progressive weakening of Si-O bonding due to antibonding-state occupation. From the electronic and phonon band structures, we estimated the Frohlich coupling constant, which decreases as $T_e$ increases, suggesting a crossover to a nonpolar phase of $α$-SiO$_2$ at elevated electronic temperature. This is corroborated by the Bader charge analysis. We also suggest that polar optical phonon scattering should be strongly suppressed at $T_e > 2$ eV. From large-cell DNNP-MD simulations, we show that a well-defined thermal equilibrium, as defined by the Maxwell-Boltzmann distribution, is not achieved over the first few hundred femtoseconds. This behavior explains the non-monotonic equilibration of the kinetic temperature after a sudden rise of $T_e$. After $T_e$ is raised to 2.6 eV, Si and O atoms first equilibrate separately at two different temperatures, suggesting an atomic fluid phase, in agreement with recent experimental and theoretical findings.
