论文标题
第一原理研究二氧化硅玻璃和prigogine-defay比率的特定热量跳跃
First-principles study on the specific heat jump in the glass transition of silica glass and the Prigogine-Defay ratio
论文作者
论文摘要
玻璃过渡的最重要特征是特定热量$ΔC_{p} $的跳跃。尽管它具有重要意义，但没有任何标准理论来描述它。在这项研究中，使用第一原理分子动力学（MD）模拟来描述硅胶的玻璃跃迁，这带来了许多挑战。将状态变量扩展到包含原子$ \ {\ bar {\ bf r} _ {j} \} $的新颖观点，包括原子的平衡位置。将内部能量分解为三个组件（结构，声子和热膨胀能）表明，硅胶的跳跃$ΔC_{p} $完全取决于结构能的成分。小$ΔC_{p} $的原因是其高玻璃转换温度，这使得结构能量的波动对温度变化不敏感。这显着影响了prigogine-defay比率$ \itπ$的解释方式，这是以前未知的。比率$ \itπ$代表总能量变化与玻璃过渡时热膨胀能的贡献的比率。 $ \itπ> 1 $的一般特性表明玻璃转变主要是由于结构能的变化而发生。二氧化硅玻璃是一个极端的情况，因为过渡完全是由于内部结构的变化而发生的，例如Si-O--Si键的弯曲角度的分布。
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.
