[QE-users] R: R: R: Reading displacements from the matdyn.modes file

[Pietro Davide Delugas]

You must preserve the proportion --and, if the displacements are complex,  the phase differences- among the mode components.

Your procedure doesn't do that unless you write the displaced geometry in fractional coordinates and your system is orthorhombic.

It's much simpler to use alat coordinates so that you can add the scaled displacement as it is.
Pietro


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Da: users <users-bounces at lists.quantum-espresso.org> per conto di Piotr Szkudlarek <p.szkudlarek at cent.uw.edu.pl>
Inviato: mercoledì 25 gennaio 2023 14:54
A: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Oggetto: Re: [QE-users] R: R: Reading displacements from the matdyn.modes file

Dear Pietro,
to create the displaced geometries, I added the 1st, 3rd and 5th number in the matrix divided by x, y and z cell sizes and then multiplied by an arbitral scaling factor (in my case - 0.1)). Is that a proper way to create the displaced geometry?
Yours sincerely.,
Piotr Szkudlarek

śr., 25 sty 2023 o 14:48 Pietro Davide Delugas <pdelugas at sissa.it<mailto:pdelugas at sissa.it>> napisał(a):
Dear Piotr
It is just a normalized 3Xnat vector  --normalized such that the sum of the squared moduli of all displacements yields one. They give you the relative amplitudes and phases of the atomic displacements in that mode.  The net amplitude would depend on the energy stored in that mode and its reduced mass.

Hope it helps
Pietro
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Da: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> per conto di Piotr Szkudlarek <p.szkudlarek at cent.uw.edu.pl<mailto:p.szkudlarek at cent.uw.edu.pl>>
Inviato: mercoledì 25 gennaio 2023 13:22
A: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Oggetto: Re: [QE-users] R: Reading displacements from the matdyn.modes file

Dear Pietro,
Thank you very much for your answer. I have another question: are those numbers in Angstrom or what units?
Regards,
Piotr Szkudlarek


pon., 23 sty 2023 o 11:28 Pietro Davide Delugas <pdelugas at sissa.it<mailto:pdelugas at sissa.it>> napisał(a):
Hello Piotr
The displacements' components are complex numbers; thus, six floats.

Pietro
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Da: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> per conto di Piotr Szkudlarek <p.szkudlarek at cent.uw.edu.pl<mailto:p.szkudlarek at cent.uw.edu.pl>>
Inviato: lunedì 23 gennaio 2023 10:55
A: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Oggetto: [QE-users] Reading displacements from the matdyn.modes file

Dear QE community,
I would like to ask what is the meaning of 6 floats in matdyn.modes file. I can imagine that 3 of them show the coordinates of the displacements, but what are the other three? Also, which of them are the ones telling about the coordinates of the displacement?
Best,
Piotr Szkudlarek,
University of Warsaw
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