[QE-developers] Patch to modify the pw.x behavior at user-provided k-point list

[Yunzhe Wang]

Dear Professors and Developers,


Sorry about the bothering long mail!


Our group has built a server to generate the least-number k-point mesh for a user-given length of the corresponding supercell size. (By "corresponding", I mean a calculation with a dense k-point mesh for a primitive cell, is equivalent to, a calculation with a large supercell with 1 k-point). Currently, the server is able to read the user input file and append the returned K_POINTS card at the end.


However, during the beta testing, we found that QE had the subroutine irreducible_BZ() to force the mesh being expand by the lattice point symmetries first, and then being reduced by the true crystal symmetry. Our server already returns a mesh complying with the crystal symmetry, but will be expanded quite a lot (even more in the low symmetry case) by irreducible_BZ().


So my question is, is there a specific reason to let the mesh being expanded by the lattice symmetry first? Our beta test results show the two cases, expanded and not-expanded (initial K_POINTS card in both cases provided by our server), has nearly the same total energy. And the converged energy by the not-expanded one is also very close to that of the MP generated k-point mesh.


We have wrote a small patch to include an additional flag "kpuser" to switch on and off the expansion, and when it's off, we leave the behavior of QE untouched. Do you think it's ok that we release the patch and let users of our server to patch their local QE distribution? Or we open an issue on QE and let the experts of QE to scrutinize this feature, if you think it's valuable to be incorporated in?


Best Regards,

Yunzhe(Phil) Wang, Graduate Student

Mueller Research Group,

Johns Hopkins University


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