search

tdep-developers / tdep

The Temperature Dependent Effective Potentials (TDEP) code
MIT License
58 stars 22 forks source link

[ERROR] negative phonon frequency in TDEP #81

Closed WenjiangZhou closed 2 months ago

WenjiangZhou commented 2 months ago

Hello, Dear TDEP developer, I used TDEP to extract the phonon band, but I meet a negative phonon frequency. I'm sure my material is stable and the phonon from DFPT (VASP) is quite good. Do you have any suggestions to help me solve this question? Thank you very much.

TDEP: image

DFPT: image

mjv500 commented 2 months ago

Hello,

you are running a 2D material, and it seems you have issues with the interpolation. For TDEP there is a flag you can play with ( no rotational), for 2D materials but also hermiticity and Huang invariances. Try turning them all off to begin with.

https://tdep-developers.github.io/tdep/program/extract_forceconstants/

Matthieu

On Mon, Jul 29, 2024 at 2:24 PM WenjiangZhou @.***> wrote:

Hello, Dear TDEP developer, I used TDEP to extract the phonon band, but I meet a negative phonon frequency. I'm sure my material is stable and the phonon from DFPT (VASP) is quite good. Do you have any suggestions to help me solve this question? Thank you very much.

TDEP: image.png (view on web) https://github.com/user-attachments/assets/5a127015-fb5e-46f0-864c-7937130e1ea3

DFPT: image.png (view on web) https://github.com/user-attachments/assets/e4d548b9-7715-45ee-82ad-4fce9978c5af

— Reply to this email directly, view it on GitHub https://github.com/tdep-developers/tdep/issues/81, or unsubscribe https://github.com/notifications/unsubscribe-auth/ABWOT3YSKJXFDOZ3N5F6HYTZOYYBFAVCNFSM6AAAAABLUFLRL6VHI2DSMVQWIX3LMV43ASLTON2WKOZSGQZTKMRXHAYTQOA . You are receiving this because you are subscribed to this thread.Message ID: @.***>

-- 


Professor Matthieu J Verstraete
Fellow, American Physical Society
Chair, Steering Committee, European Theoretical Spectroscopy Facility
www.etsf.eu
Alumnus Fellow, Young Academy of Europe  yacadeuro.org

Institute for Theoretical Physics (ITP) Department of Physics
Buys Ballot Gebouw/Building, Princetonplein 5, office
University of Utrecht,  3584 CC Utrecht
ITP Secretariat: +31 30 253 5928 E-mail: ***@***.***

Group web page (Liège): http://www.nanomat.ulg.ac.be/

Nanomat lab, Q-Mat center, Université de Liège
Département de Physique, Bat. B5a, 4/50
Allée du 6 août, 19 B-4000 Sart Tilman, Liège Belgium
Phone : +32 4 366 90 17

European Theoretical Spectroscopy Facility (ETSF)

Mail : ***@***.***
          ***@***.***
          ***@***.***
WenjiangZhou commented 2 months ago

Thank you very much. I've solved this issue when I turn off the Huang invariances. I also find that you think deriving the proper invariances for a two-dimensional material is necessary. I'd like to contribute more if have chances.