First-principles study of phonon anharmonicity and negative thermal expansion in ScF3
First-principles study of phonon anharmonicity and negative thermal expansion in ScF3
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DOI：
10.1103/physrevmaterials.3.033601
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发表时间：
2019-03-05
影响因子：
3.4
通讯作者：
Tsuneyuki, Shinji
中科院分区：
文献类型：
--
作者：
Oba, Yusuke;Tadano, Terumasa;Tsuneyuki, Shinji
采用基于密度泛函理论的非简谐自由能方法研究了立方相三氟化钪（ScF3）大负热膨胀的微观起源.我们表明，传统的准谐波近似（QHA）完全打破ScF3和四次非谐性，处理非微扰的自洽声子理论，是必不可少的再现所观察到的过渡从负到正的热膨胀系数和硬化的R4+软模加热。此外，我们表明，从三次非谐性的振动自由能的贡献，由改进的自洽声子理论评估，是显着的和重要的，从四次非谐性的强大的理解的热膨胀系数的温度依赖性。本研究的第一性原理方法使我们能够计算各种热力学性质的固体在热力学极限的三次和四次非谐性的影响。因此，它有望解决许多已知的问题，特别是在高温和强非谐材料的QHA为基础的预测显着。
The microscopic origin of the large negative thermal expansion of cubic scandium trifluorides (ScF3) is investigated by performing a set of anharmonic free-energy calculations based on density functional theory. We demonstrate that the conventional quasiharmonic approximation (QHA) completely breaks down for ScF3 and the quartic anharmonicity, treated nonperturbatively by the self-consistent phonon theory, is essential to reproduce the observed transition from negative to positive thermal expansivity and the hardening of the R4+ soft mode with heating. In addition, we show that the contribution from the cubic anharmonicity to the vibrational free energy, evaluated by the improved self-consistent phonon theory, is significant and as important as that from the quartic anharmonicity for robust understandings of the temperature dependence of the thermal expansion coefficient. The first-principles approach of this study enables us to compute various thermodynamic properties of solids in the thermodynamic limit with the effects of cubic and quartic anharmonicities. Therefore, it is expected to solve many known issues of the QHA-based predictions particularly noticeable at high temperature and in strongly anharmonic materials.