First-Principles Prediction of Temperature-Dependent Phonon Energy Shifts*

Phonon energies of solids at finite temperatures shift from their harmonic values at 0 K due to anharmonicity. Accurate prediction of the frequency shifts is necessary for the study of many areas such as thermal transport, thermodynamical properties, superconductivity, infrared spectroscopy, etc. Here, we report first-principles simulations that predict the temperature-dependent thermal expansion coefficients and phonon energy shifts of monolayer and bulk boron nitride. The calculation results agree with available experimental results. We have also decomposed the frequency shifts into distinct contributions, accounting for the experimental results. The predicted phonon energy shifts are also in agreement with recent experimental measurements in bulk boron nitride using electron energy gain and loss spectroscopies [1]. The first-principles calculations, combined with experiments, show a capability of measuring temperature with nanoscale resolution.

[1] J. C. Idrobo et al., Temperature measurement by a nanoscale electron probe using energy gain and loss spectroscopy, APS March meeting, 2018.