具有纯非谐性的核量子效应与硅的反常热膨胀。
Nuclear quantum effect with pure anharmonicity and the anomalous thermal expansion of silicon.
机构信息
Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA 91125;
Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA 91125.
出版信息
Proc Natl Acad Sci U S A. 2018 Feb 27;115(9):1992-1997. doi: 10.1073/pnas.1707745115. Epub 2018 Feb 13.
Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well understood. Adapting harmonic phonons to the specific volume at temperature, the quasiharmonic approximation, has become accepted for simulating the thermal expansion, but has given ambiguous interpretations for microscopic mechanisms. To test atomistic mechanisms, we performed inelastic neutron scattering experiments from 100 K to 1,500 K on a single crystal of silicon to measure the changes in phonon frequencies. Our state-of-the-art ab initio calculations, which fully account for phonon anharmonicity and nuclear quantum effects, reproduced the measured shifts of individual phonons with temperature, whereas quasiharmonic shifts were mostly of the wrong sign. Surprisingly, the accepted quasiharmonic model was found to predict the thermal expansion owing to a large cancellation of contributions from individual phonons.
尽管硅在现代技术中被广泛应用，但人们对其特殊的热膨胀性质仍了解不足。准谐近似通过调整声子在温度下的特定体积来适应热膨胀，已被广泛用于模拟热膨胀，但对微观机制的解释却存在歧义。为了验证原子机制，我们对单晶硅进行了从 100 K 到 1500 K 的非弹性中子散射实验，以测量声子频率的变化。我们采用最先进的从头算计算方法，充分考虑了声子的非谐性和核量子效应，重现了实验测量的单个声子随温度的移动，而准谐移动大多是错误的。令人惊讶的是，人们发现被广泛接受的准谐模型能够预测热膨胀，这是由于单个声子的贡献相互抵消的结果。
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