Wu Yu-Ning, Saidi Wissam A, Wuenschell Jeffrey K, Tadano Terumasa, Ohodnicki Paul, Chorpening Benjamin, Duan Yuhua
National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States.
J Phys Chem Lett. 2020 Apr 2;11(7):2518-2523. doi: 10.1021/acs.jpclett.0c00183. Epub 2020 Mar 16.
Soft phonon modes in strongly anharmonic crystals are often neglected in calculations of phonon-related properties. Herein, we experimentally measure the temperature effects on the band gap of cubic SrTiO, and compare with first-principles calculations by accounting for electron-phonon coupling using harmonic and anharmonic phonon modes. The harmonic phonon modes show an increase in the band gap with temperature using either Allen-Heine-Cardona theory or finite-displacement approach, and with semilocal or hybrid exchange-correlation functionals. This finding is in contrast with experimental results that show a decrease in the band gap with temperature. We show that the disagreement can be rectified by using anharmonic phonon modes that modify the contributions not only from the significantly corrected soft modes, but also from the modes that show little correction in frequencies. Our results confirm the importance of soft-phonon modes that are often neglected in the computation of phonon-related properties and particularly in electron-phonon coupling.
在强非谐晶体中，软声子模式在与声子相关性质的计算中常常被忽略。在此，我们通过实验测量了温度对立方SrTiO带隙的影响，并通过使用简谐和声子非谐模式考虑电子-声子耦合，与第一性原理计算结果进行了比较。使用艾伦-海涅-卡尔多纳理论或有限位移方法，以及半局域或杂化交换关联泛函时，简谐声子模式显示带隙随温度升高。这一发现与实验结果相反，实验结果表明带隙随温度降低。我们表明，通过使用非谐声子模式可以纠正这种不一致，非谐声子模式不仅改变了显著修正的软模式的贡献，还改变了频率修正很小的模式的贡献。我们的结果证实了软声子模式的重要性，软声子模式在与声子相关性质的计算中，特别是在电子-声子耦合计算中常常被忽略。
