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I have been working on CsCl using Quantum ESPRESSO, and I calculated both the electronic band structure and phonons using Ultrasoft Pseudopotentials (USPP) and GGA.

Surprisingly, the electronic structure turned out to be qualitatively very accurate and aligned well with results from other studies. However, the phonon properties are far from satisfactory—they differ significantly from what is reported in other studies of this material.

Does anyone have insights into why this might be happening? Thanks in advance for your help!

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    $\begingroup$ You should, at the very least, show the plots you obtained, and how you ran the phonon $\endgroup$
    – naturallyInconsistent
    Commented Nov 19 at 2:59

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I suggest performing a high-quality threshold calculation. Electronic structure calculations do not require as high quality threshold as phonon calculations. (High-quality threshold means from 10⁻¹⁷ to 10⁻¹⁴.) I am aware that phonon calculations need highly accurate atomic positions.

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  • $\begingroup$ Thank you! I'm gonna try soon! $\endgroup$
    – Martino Napoli
    Commented Nov 19 at 9:04
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    $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Commented Nov 19 at 14:07
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Phonon dispersion basically depends on atomic positions, lattice constant (overall system structure). When you run DFT, you do relax and vc relax and you get equilibrium structure finally. That means, the atomic position you are using, doesn't represent the position at finite temperature. You need to perform molecular dynamics simulation to get the temperature dependent atomic position. After that, if you plot phonon dispersion you might get the exact match!

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