Dynamics of silica glass: two-level tunnelling states and low-energy floppy modes
Dynamics of silica glass: two-level tunnelling states and low-energy floppy modes
复制标题
石英玻璃动力学：两级隧道态和低能软盘模式
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
V. Heine
中科院分区：
文献类型：
--
作者：
K. Trachenko;M. Dove;M. Harris;V. Heine
我们提出了硅玻璃低能动力学的计算研究结果。分子动力学模拟结果表明，部分玻璃结构可以发生SiO4四面体的大规模协同取向。这些运动涉及大约30个四面体的重新定向，能量势垒约为0.06 eV。我们将这些运动与双阱势的存在联系起来，从而在模型中产生两能级隧道态，从而为玻璃的异常低温热性能提供了机制。对较大结构二氧化硅玻璃的模拟表明，跳跃事件变得更加频繁，并且彼此之间不相关。除了研究大四面体重排时二氧化硅玻璃的柔韧性外，我们还研究了二氧化硅玻璃在维持低-？软盘模式。后半部分的研究得到了非弹性中子散射数据的支持，在0-10？meV和散射矢量范围0-8? -1。通过将最初为结晶硅酸盐开发的刚性单元模式模型应用于二氧化硅玻璃结构的分析，我们发现二氧化硅玻璃在支持低？软盘模式。通过对计算得到的硅玻璃及其结晶相的振动密度进行比较，得出了同样的结论，并在非弹性中子散射数据中得到了证实。
We present the results of a computational study of the low-energy dynamics of silica glass. Molecular dynamics simulation results show that parts of the glass structure can undergo large cooperative reorientations of SiO4 tetrahedra. These motions involve reorientations of about 30 tetrahedra with an energy barrier of about 0.06?eV. We relate these motions to the presence of double-well potentials which give rise to two-level tunnelling states in the model, thereby providing the mechanism for the anomalous low-temperature thermal properties of glasses. Simulation of larger structures of silica glass shows that jump events become more frequent and uncorrelated with each other. In addition to studying the flexibility of silica glass in terms of the large tetrahedral rearrangements, we also address the flexibility of silica glass in terms of its ability to sustain low-? floppy modes. The latter part of the study is supported by inelastic neutron scattering data, and we compare experimental and calculated dynamic structure factors in the energy range 0-10?meV and scattering vector range 0-8??-1. By applying the analysis of the rigid-unit-mode model as initially developed for crystalline silicates to structures of silica glass we find that silica glass is surprisingly similar to its corresponding crystalline phases in its ability to support low-? floppy modes. The same conclusion follows from the comparison of calculated vibrational densities of states of silica glass and its crystalline phases, and is borne out in the inelastic neutron scattering data.