MD velocities and py4vasp

[xiliang_lian]

Hello,

I am doing MD calculations with VASP 6.3.2 and am interested in some properties related to velocities. I didn't find many descriptions on your wiki. A quick search on the Internet doesn't give much helpful information; some information is outdated. I checked the "vaspout.h5" file and it seems velocities have been written to this file if I understand correctly.

Therefore, I want to ask whether you can provide this feature in py4vasp or provide other suggestions/scripts so it is easy to extract velocities. Thanks a lot in advance.

Best regards,
Xiliang

[henrique_miranda]

Hi Xiliang,

Thank you for your suggestion, we will seek to include this feature in a future release of py4vasp.

[xiliang_lian]

Hi,

For the moment, do you have any advice on how I can properly get velocities? I assume it will take some time for me to get your new release.

Thanks in advance.

Best,
Xiliang

[henrique_miranda]

Actually, the ion velocities are only written to the CONTCAR but that is overwritten at every MD step.
In the hdf5 file they are only written in the last step in '/results/positions/ion_velocities' for the final structure.

If you need velocities at every time step, our suggestion would be to read the positions at every MD step (you can actually read them with py4vasp) and compute the velocity using finite differences or something more sophisticated.
When computing the differences between the positions at every step you need to account for periodic boundary conditions!

[xiliang_lian]

okay, thank you very much for the suggestions.

[martin.schlipf]

I implemented this in py4vasp now. It will then work with the next release of VASP.

[xiliang_lian]

Great news. That's very kind of you. Thank you very much and looking forward to seeing the next release.