[QE-users] Reduced mass?

Mon Oct 14 15:31:53 CEST 2024

Dear Pietro,

Thank you very much. I basically just need the value, to be able to tell how big it is.

Do I understand the basics correctly? Bold u_k^v is a matrix of cartesian displacements of the same size as is the atom coordinate matrix (G)? The one that ends up in the molden file? Can I travel along the mode by making geometries of a * u + G, "a" being an arbitrary scalar (yeah, I know it's only relevant near the minimum).

As for the value of the reduced mass: just eyeballing it - it's going to be in the order of magnitude of a simple algebraic average mass of the atoms in the cell, something like 10-100 amu. Is that physically relevant? I mean, an actual phonon lives in a whole crystal, with ~N_Avogadro atoms vibrating. If it's not the whole crystal vibrating but a wavepacket inside crystal - it might as well involve any number of atoms between the whole crystal and a few atoms. Shouldn't the respective reduced mass be in the order of magnitude of about ~10 * N_atoms? What would be the relevant literature for this problem?

Thank you

On 10/14/24 14:42, Pietro Davide Delugas wrote:
Hello
Generally, the reduced mass of the phonon modes is not very useful because it is implicitly included in the normalization of their displacements, and introducing it explicitly would only complicate things.
However, one definition of the reduced mass could be:

[cid:part1.uZQic9IP.BTgnTNhx at uwr.edu.pl]
Where k is the index running on all atoms, m_k is the mass, and u_k are the displacements of the mode.

Here are some notes https://hackmd.io/@pietrodelugas/r1SykO511l
Pietro
________________________________
From: users <users-bounces at lists.quantum-espresso.org><mailto:users-bounces at lists.quantum-espresso.org> on behalf of Andrii Shyichuk via users <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Sent: Saturday, October 12, 2024 01:21
To: users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org> <users at lists.quantum-espresso.org><mailto:users at lists.quantum-espresso.org>
Subject: [QE-users] Reduced mass?

Dear Users,

How do I get the reduced mass of a vibrational (phonon) mode from (I
guess) PH.X?

I assume it must be calculated somewhere, but it is not printed. It is
not mentioned in the PH manual (searched for "mass") and it looks like
nobody asked it here (searched for "reduced mass").

Thank you.

Best regards.

dr Andrii Shyichuk, Faculty of Chemistry, University of Wrocław

dr Andrii Shyichuk
ADIUNKT
Zakład Chemii Nieorganicznej, Wydział Chemii

Uniwersytet Wrocławski
ul. F. Joliot-Curie 14
50-383 Wrocław
tel. +48 71 375 72 65

[cid:part2.BxClowrP.UKz0RWlQ at uwr.edu.pl]<https://uni.wroc.pl>[cid:part3.8ETV2hn4.s2r2ZhnP at uwr.edu.pl]<https://uwr.edu.pl/inicjatywa-doskonalosci-uczelnia-badawcza/>[cid:part4.flWbfyXe.WQQGAkwG at uwr.edu.pl]

Wiadomość ta oraz wszelkie załączone do niej pliki są poufne i mogą być prawnie chronione. Jeżeli nie jest Pani/Pan zamierzonym adresatem niniejszej wiadomości, nie może Pani/Pan jej ujawniać, kopiować, dystrybuować ani też w żaden inny sposób udostępniać lub wykorzystywać. O błędnym zaadresowaniu wiadomości proszę niezwłocznie poinformować nadawcę i usunąć wiadomość.

dr Andrii Shyichuk
ADIUNKT
Zakład Chemii Nieorganicznej, Wydział Chemii

Uniwersytet Wrocławski
ul. F. Joliot-Curie 14
50-383 Wrocław
tel. +48 71 375 72 65

[cid:2022_02_uwr_arqus_pocitedostopki_bdb4c7bb-1172-4107-90f8-1b2742af358e.png]<https://uni.wroc.pl>[cid:2022_02_uwr_arqus_pocitedostopki3_e5829564-9e6b-4628-ac3b-6e1d97627e4b.png]<https://uwr.edu.pl/inicjatywa-doskonalosci-uczelnia-badawcza/>[cid:2022_02_uwr_arqus_pocitedostopki4_89c9e33b-31a4-4974-a07d-b817a789344c.png]

Wiadomość ta oraz wszelkie załączone do niej pliki są poufne i mogą być prawnie chronione. Jeżeli nie jest Pani/Pan zamierzonym adresatem niniejszej wiadomości, nie może Pani/Pan jej ujawniać, kopiować, dystrybuować ani też w żaden inny sposób udostępniać lub wykorzystywać. O błędnym zaadresowaniu wiadomości proszę niezwłocznie poinformować nadawcę i usunąć wiadomość.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Outlook-hyieetau.png
Type: image/png
Size: 17175 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki_bdb4c7bb-1172-4107-90f8-1b2742af358e.png
Type: image/png
Size: 4800 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0001.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki3_e5829564-9e6b-4628-ac3b-6e1d97627e4b.png
Type: image/png
Size: 1710 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0002.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki4_89c9e33b-31a4-4974-a07d-b817a789344c.png
Type: image/png
Size: 2126 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0003.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki_bdb4c7bb-1172-4107-90f8-1b2742af358e.png
Type: image/png
Size: 4800 bytes
Desc: 2022_02_uwr_arqus_pocitedostopki_bdb4c7bb-1172-4107-90f8-1b2742af358e.png
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0004.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki3_e5829564-9e6b-4628-ac3b-6e1d97627e4b.png
Type: image/png
Size: 1710 bytes
Desc: 2022_02_uwr_arqus_pocitedostopki3_e5829564-9e6b-4628-ac3b-6e1d97627e4b.png
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0005.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2022_02_uwr_arqus_pocitedostopki4_89c9e33b-31a4-4974-a07d-b817a789344c.png
Type: image/png
Size: 2126 bytes
Desc: 2022_02_uwr_arqus_pocitedostopki4_89c9e33b-31a4-4974-a07d-b817a789344c.png
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20241014/04a05da3/attachment-0006.png>