[QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

[Kazume NISHIDATE]

Dear Shubham,

I’m not an expert on the phonon calculation.
But it may be in a wavelength unit.

The bottom of the curve in the left-hand graph is around 25  meV.

25 meV = 0.025 eV

0.025 eV is around 50 micro m  (wavelength).
https://sherwingroup.itst.ucsb.edu/internal/unit-conversion/

= 50 x 10^(-6) m
= 50 x 10^(-6) x 100 cm
= 50 x 10^(-4) cm
= 5 x 10^(-3) cm
= 0.005 cm

It is around the bottom of the curve in the right-hand graph.



> 2025/04/09 0:03、Shubham Patel <spatelphy at iitkgp.ac.in>のメール:
> 
> Dear developers and users,
> 
> I am trying to calculate the frequencies (freqs) using Quantum Espresso PHonon calculations as well as using dynamical matrices generated using matdyn.x. I find that there is a unit mismatch in the freqs which gives rise to a magnitude difference. In the first case, I calculate phonon band structure using matdyn.x --> plotband.x. While in the second case I generate dynamical matrices using matdyn.x and then diagonalize the matrices along the kpath and generated exactly same band dispersion except the magnitude on the y-axis (frequency range). Could anyone please tell what is this factor which brings the magnitude mismatch? I am also attaching a figure to compare.
> 
> Thank you very much for any help.
> 
> Sincerely,
> Shubham<phdos_AZX_mimatch.pdf>__________________________________________________



西館数芽
Kazume NISHIDATE Ph.D

Department of Systems Innovation Engineering,
Graduate School of Science and Engineering, Iwate University
4-3-5 Ueda, Morioka, Iwate, 020-8551 JAPAN
Phone:+81-19-621-6391
kazume.nishidate at gmail.com, nisidate at iwate-u.ac.jp
https://sites.google.com/site/nisidatelab/