School of Physics and Astronomy, Queen Mary University of London, London, UK.
J Phys Condens Matter. 2013 Jun 12;25(23):235401. doi: 10.1088/0953-8984/25/23/235401. Epub 2013 May 16.
We propose a simple new way to evaluate the effect of anharmonicity on a system's thermodynamic functions, such as heat capacity. In this approach, the contribution of all the potentially complicated anharmonic effects to the constant-volume heat capacity is evaluated using one parameter only: the coefficient of thermal expansion. Importantly, this approach is applicable not only to crystals, but also to glasses and viscous liquids. To support this proposal, we perform molecular dynamics simulations of several crystalline and amorphous solids as well as liquids, and find a good agreement between the results from theory and simulations. We observe an interesting non-monotonic behavior of the liquid heat capacity with a maximum, and explain this effect as being a result of competition between anharmonicity at low temperature and decreasing number of transverse modes at high temperature.
我们提出了一种简单的新方法来评估非谐效应对系统热力学函数（如热容）的影响。在这种方法中，仅使用一个参数来评估所有潜在复杂的非谐效应对定容热容的贡献：热膨胀系数。重要的是，这种方法不仅适用于晶体，也适用于玻璃和粘性液体。为了支持这一建议，我们对几种晶体和非晶固体以及液体进行了分子动力学模拟，并发现理论和模拟结果之间有很好的一致性。我们观察到液体热容具有有趣的非单调行为，存在最大值，并将这种效应解释为低温下的非谐性与高温下横向模式数量减少之间的竞争结果。
