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

[Stefano Baroni]

The dynamical matrix is a second derivative of an energy with respect to atomic displacements (units: energy/length^2). Frequencies are inverses of time (units: 1/time). energies are frequencies times (no pun intended) an action unit, called “h” by practitioners. The relation between the three is explained in any elementary solid-state textbook (those old-fashioned bundles of paper stained with minuscle characters impressed with a dark dye called ink). The information contained in these bundles once formed the basis of the knowledge (or lack thereof) now spread through youtube channels. Hope this helps. SB

___
Stefano Baroni, Trieste -- http://stefano.baroni.me

On 16 Apr 2025, at 05:54, Shubham Patel <spatelphy at iitkgp.ac.in> wrote:


Dear Prof. Stefano,

Thank you for your reply. I did not receive your message on my email that is why I missed it.

When I diagonalize the q dependent matrices I can obtain the eigenvalues (frequencies) from which I am getting the correct phonon dispersion but the frequency range is not correct as I had shown in a figure I previously attached. Even if I multiply now with 13.6 eV (13600 meV) to convert Ryd to meV I am not able to reproduce the frequency range. Could you please suggestle what factor I am missing here?

Thank you very much.

Sincerely,
Shubham

________________________________
From: "Stefano de Gironcoli" <degironc at sissa.it>
To: "Quantum ESPRESSO users Forum" <users at lists.quantum-espresso.org>
Sent: Tuesday, April 15, 2025 9:25:04 PM
Subject: Re: [QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

Ryd/au^2 ... as already stated in my previous reply
Stefano

Get Outlook for Android<https://aka.ms/AAb9ysg>
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Shubham Patel <spatelphy at iitkgp.ac.in>
Sent: Tuesday, April 15, 2025 5:45:37 PM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

Hello again,

Could anyone please tell?

Sincerely,
Shubham

----- Original Message -----
From: "Shubham Patel" <spatelphy at iitkgp.ac.in>
To: "Quantum ESPRESSO users Forum" <users at lists.quantum-espresso.org>
Sent: Friday, April 11, 2025 3:28:53 PM
Subject: Re: [QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

Hi,

Could someone please tell what is the unit of dynamical matrix elements'. I have to do some post processing from the dynamical matrices and therefore I want to know the proper units of the elements.

Thank you,
Shubham

----- Original Message -----
From: "Shubham Patel" <spatelphy at iitkgp.ac.in>
To: "Quantum ESPRESSO users Forum" <users at lists.quantum-espresso.org>
Sent: Wednesday, April 9, 2025 8:09:58 AM
Subject: Re: [QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

Dear Kazume NISHIDATE,

Thank you very much for your prompt reply. This is indeed correct what you observed. However, when I divide the y scale of right hand side figure with 0.005 it should return the left figure but it does not. Attaching the modified figure in the right most (dividing with 0.005). Am I missing something?

Thank you,
Shubham

----- Original Message -----
From: "Kazume NISHIDATE" <nisidate at iwate-u.ac.jp>
To: "Quantum ESPRESSO users Forum" <users at lists.quantum-espresso.org>
Sent: Wednesday, April 9, 2025 1:54:59 AM
Subject: Re: [QE-users] unit mismatch between PH generated frequencies and manually generated eigenvalues

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/

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_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list users at lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users
_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list users at lists.quantum-espresso.org
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