Statistical Physics Group, Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, CB3 0AS Cambridge, United Kingdom.
Grup de Caracterizacio de Materials, Departament de Fisica, EEBE, Barcelona Research Center in Multiscale Science and Engineering, Universitat Politecnica de Catalunya, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia.
Phys Rev E. 2018 May;97(5-1):053001. doi: 10.1103/PhysRevE.97.053001.
We use a microscopically motivated generalized Langevin equation (GLE) approach to link the vibrational density of states (VDOS) to the dielectric response of orientational glasses (OGs). The dielectric function calculated based on the GLE is compared with experimental data for the paradigmatic case of two OGs: freon-112 and freon-113, around and just above T_{g}. The memory function is related to the integral of the VDOS times a spectral coupling function γ(ω_{p}), which tells the degree of dynamical coupling between molecular degrees of freedom at different eigenfrequencies. The comparative analysis of the two freons reveals that the appearance of a secondary β relaxation in freon-112 is due to cooperative dynamical coupling in the regime of mesoscopic motions caused by stronger anharmonicity (absent in freon-113) and is associated with the comparatively lower boson peak in the VDOS. The proposed framework brings together all the key aspects of glassy physics (VDOS with the boson peak, dynamical heterogeneity, dissipation, and anharmonicity) into a single model.
我们使用基于微观的广义朗之万方程（GLE）方法将振动态密度（VDOS）与取向玻璃（OG）的介电响应联系起来。基于 GLE 计算的介电函数与两个 OG 的典型案例（氟利昂-112 和氟利昂-113）的实验数据进行了比较，这些案例涉及玻璃化转变温度（T_g）上下附近的温度范围。记忆函数与 VDOS 的积分乘以谱耦合函数 γ(ω_{p})有关，该函数反映了不同本征频率下分子自由度之间的动态耦合程度。对这两种氟利昂的比较分析表明，氟利昂-112 中出现的次要β弛豫是由于介观运动状态下的协同动力学耦合引起的，这种动力学耦合是由更强的非谐性（氟利昂-113 中不存在）引起的，并且与 VDOS 中相对较低的玻色峰有关。所提出的框架将玻璃物理的所有关键方面（具有玻色峰的 VDOS、动力学非均匀性、耗散和非谐性）结合到一个单一的模型中。
