石英玻璃玻璃化转变中specific heat跃迁和Prigogine-Defay比的第一性原理研究
First-principles study on the specific heat jump in the glass transition of silica glass and the Prigogine-Defay ratio
摘要：
玻璃化转变的最重要特征是比热$ΔC_{p}$的跳跃。尽管它的意义，没有标准的理论存在来描述它。在这项研究中，第一性原理分子动力学（MD）模拟被用来描述二氧化硅玻璃的玻璃化转变，这提出了许多挑战。在对模拟结果进行分析时，充分利用了将态变量扩展到原子平衡位置$\{ \bar{\bf R}_{j} \}$的新颖观点。将内能分解为结构能、声子能和热膨胀能，发现石英玻璃的$ΔC_{p}$跃迁完全由结构能决定。小的$ΔC_{p}$的原因是其高的玻璃化转变温度，这使得结构能量的波动对温度变化不敏感。这显著影响了如何解释Prigogine-Defay比值$\itΠ$，这是以前未知的。比率$\itΠ$表示玻璃化转变时总能量变化与热膨胀能量贡献的比率。玻璃的一般性质$\itΠ>1$表明，玻璃化转变主要通过结构能的变化发生。二氧化硅玻璃是一个极端的情况，因为转变完全是通过内部结构的变化发生的，例如Si-O-Si键的弯曲角分布。
英文摘要：
The most important characteristic of glass transition is a jump in specific heat $ΔC_{p}$. Despite its significance, no standard theory exists to describe it. In this study, first-principles molecular-dynamics (MD) simulations are used to describe the glass transition of silica glass, which presents many challenges. The novel view that state variables are extended to include the equilibrium positions of atoms $\{ \bar{\bf R}_{j} \}$ is fully used in analyzing the simulation results. Decomposing the internal energy into three components (structural, phonon, and thermal expansion energies) reveals that the jump $ΔC_{p}$ of silica glass is entirely determined by the component of structural energy. The reason for the small $ΔC_{p}$ is its high glass-transition temperature, which makes the fluctuation in the structural energy insensitive to temperature changes. This significantly affects how the Prigogine-Defay ratio $\itΠ$ is interpreted, which was previously unknown. The ratio $\itΠ$ represents the ratio of the total energy change to the contribution of thermal expansion energy at the glass transition. The general property, $\itΠ>1$, of glasses indicates that glass transitions occur mainly by changes in the structural energy. Silica glass is an extreme case in that the transition occurs entirely by the change in internal structure, such as the distribution of the bending angle of Si--O--Si bond.
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