Obtain the data to calculate the irreducible representations of electronic states from the result of VASP.

[hongyi-zhao]

I have recently (found | came across) this great Py4vasp tool. I want to know if I can obtain the data to calculate the irreducible representations of electronic states from the result of VASP, say, used by irvsp, irrep, or SpaceGroupIrep?

Regards,
HZ

[martin-schlipf]

I have not used any of these tools, so I don't know what exactly you would need to do this. I suppose if you want the irrep of a band you would need to read the orbitals though. This is currently not supported by py4vasp. But you can use py4vasp to read the band structure data into a dictionary. If you have the irrep information from another tool, you could combine the results afterwards.

[hongyi-zhao]

The core/key step what I want is to obtain the trace.txt file as generated by vasp2trace which includes mainly the following three things, as commented here:

(1) Read the Bloch wavefunctions from DFT results.
(2) Transform the Bloch wavefunctions (rotation and translation given by a SG symmetry {R|v}). That is, obtain the Bloch wave function by doing the calculation: {R|v} | psi_i >.
(3) For degenerate energy bands, calculate the trace of {R|v}: \sum_i=1^d < psi_i | {R|v} | psi_i >. Here, d is the degeneracy, and the wave function has already been normalized.

[martin-schlipf]

I looked a bit more into the packages. It seems that two of them are not interfaced with Python, so it would be more work to link them to py4vasp. irrep is a Python package so it would probably be easier to do that. But it would probably require changes to both py4vasp as well as the other packages, so I'm not sure if any of the authors of the other packages would be willing to invest the work.

[hongyi-zhao]

They all target to generate the trace.txt file with exactly the same specification. But even only regarding the trace.txt file generation, there are still some cautions/requirements/conditions, as commented here:

1. The format of trace.txt file is only a necessary condition to be used by getBandRep.
2. Another issue is that the rotation matrices used, especially the SU(2) spin rotation matrix, have to be the same with vasp and vasp2trace.
3. Even if both the above two points are fulfilled, there is another requirement that the code should not do additional process other than calculate the trace.

EDIT: On the above question 2, some related discussions can be seen here.

[martin-schlipf]

Did you get some feedback from the developers of these packages if they want to collaborate on coming up with an interface?

[hongyi-zhao]

Nothing at the moment. If there is any news, I will post it here.

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