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2025-05-26 17:34:00 +08:00
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@@ -50,11 +50,10 @@ Further details are provided in the appendix.
The Raman tensors and frequencies of the negligible-polar phonons were calculated using first-principles methods, The Raman tensors and frequencies of the negligible-polar phonons were calculated using first-principles methods,
and the results are compared with both experimental data and theoretical predictions (@table-nopol). and the results are compared with both experimental data and theoretical predictions (@table-nopol).
The calculated phonon frequencies show good agreement with experimental data, The calculated phonon frequencies show good agreement with experimental data with a slight underestimation of 2-5%,
with a slight underestimation of 2-5%, where the error may be attributed to the underestimation of interatomic forces by the PBE functional (cite).
which may be attributed to the underestimation of forces by PBE functional (cite).
The calculated Raman tensors are also consistent with experimental and theoretical results. The calculated Raman tensors are also consistent with experimental and theoretical results.
Among negligible-polar modes, the E#sub[2] mode observed experimentally at 776 cm#super[-1] (mode 8) Among negligible-polar modes, the E#sub[2] mode at 776 cm#super[-1] in experiment (mode 8)
exhibits the highest Raman intensity, exhibits the highest Raman intensity,
followed by four modes with lower intensities that are also experimentally visible, followed by four modes with lower intensities that are also experimentally visible,
including the E#sub[2] modes at 195.5 cm#super[-1] (mode 1) and 203.3 cm#super[-1] (mode 2), including the E#sub[2] modes at 195.5 cm#super[-1] (mode 1) and 203.3 cm#super[-1] (mode 2),
@@ -63,13 +62,14 @@ The E#sub[1] mode calculated at 746.91 cm#super[-1] (mode 7)
and the E#sub[2] mode calculated at 756.25 cm#super[-1] (mode 9) and the E#sub[2] mode calculated at 756.25 cm#super[-1] (mode 9)
are predicted to have much weaker Raman intensities and are located close to the most intense mode (mode 8), are predicted to have much weaker Raman intensities and are located close to the most intense mode (mode 8),
making them indistinguishable in experimental spectra. making them indistinguishable in experimental spectra.
This explains their absence in experimental observations.
Additionally, the A#sub[1] mode calculated at 812.87 cm#super[-1] (mode 10) Additionally, the A#sub[1] mode calculated at 812.87 cm#super[-1] (mode 10)
exhibits very weak Raman intensity in the scattering in basal plane (xx and yy, only 0.01) exhibits very weak Raman intensity in the configuration polarized in the basal-plane (xx and yy, only 0.01)
but an observable intensity in the zz configuration (1.78). but an observable intensity in the configuration polarized along z-axis (1.78).
As most Raman experiments are back-scattering along the z-direction with photon energy much less than the band gap, Since most Raman experiments are performed in a back-scattering configuration with light incident along the z-direction
this mode is generally not observed in these experiments (cite), (polarized in-plane)
but it may become detectable when the incident light does not propagate along the z-direction (as in our experiment) with photon energies much lower than the band gap,
this mode is generally not observed (cite).
However, it should become detectable when the incident light have z-direction polarization part (as in our experiment)
or when the incident light wavelength is near resonance conditions (cite). or when the incident light wavelength is near resonance conditions (cite).
Besides, there are other peeks in the experiment. Besides, there are other peeks in the experiment.