论文标题
第一原则研究玻璃过渡时玻璃的特定热量，并在甘油上进行案例研究
First-principles study on the specific heat of glass at glass transition with a case study on glycerol
论文作者
论文摘要
确定玻璃过渡的过渡温度（TG）的标准方法是特定热中的跳跃。尽管很重要，但缺乏这种跳跃的标准理论。困难包括缺乏对液体的特定热量，磁滞性以及时间表问题的缺乏。本文的第一部分提供了一种非经验方法来计算玻璃的比热。该方法由基于密度功能理论（DFT）和热力学方法的分子动力学（MD）模拟组成。基于DFT的总能量方法使我们能够计算特定的热量，而与固体或液体无关。玻璃过渡状态的一个严重问题是复杂的能量耗散过程的参与，这是通过绝热MD模拟解决的。通过将计算范围限制在平衡状态下，可以缓解磁滞问题和时间表问题。本文的第二部分描述了该理论在甘油的特定热跳（Delta CP）中的应用，以显示方法的有效性。尽管超级电池尺寸较小，但仍获得了特定热跳的合理价值。通过将Delta CP分解为结构能，声子和热膨胀部件的贡献，我们对Delta CP有一个合理的解释：对Delta CP的主要贡献来自结构能的变化。由此，获得了有关玻璃转变的整洁能量图。这项研究的结果是验证脆弱性和特定热跳跃之间的经验关系。这两个能量由比率k = tg/ delta t缩放，其中delta t是过渡的宽度，通过它通过，两个量相互关联。这对于组织各种关系的关系很有用。
The standard method to determine the transition temperature (Tg) of glass transition is the jump in the specific heat. Despite this importance, standard theory for this jump is lacking. The difficulties encompass from lack of proper treatments of specific heat of liquids, hysteresis, to the timescale issue. The first part of this paper provides a non-empirical method to calculate specific heat of glass. The method consists of molecular dynamics (MD) simulations based on density-functional theory (DFT) and thermodynamics methods. The total-energy approach based on DFT enables us to calculate specific heat, irrespective of solids or liquids. A serious problem for glass-transition states is involvement of complicated energy dissipation processes, which is resolved by adiabatic MD simulations. The problems of hysteresis and the timescale issue are alleviated by restricting the scope of calculations to equilibrium states only. The second part of this paper describes an application of the theory to the specific-heat jump (Delta Cp) of glycerol in order to show the validity of the methods. Despite severe limitations due to the small size of supercells, a reasonable value for the specific-heat jump is obtained. By decomposing Delta Cp into contributions of the structural energy, phonon, and thermal expansion parts, we have a sound interpretation for the Delta Cp: the major contribution to Delta Cp comes from the change in the structural energy. From this, a neat energy diagram about the glass transition is obtained. An outcome of this study is verification of the empirical relationship between the fragility and specific-heat jump. These two energies are scaled by the ratio k=Tg/ Delta T, where Delta T is the width of the transition, through which the two quantities are interrelated. This is useful for organizing various relationships that are found empirically.
