Warning during High-throughput hybrid BS calculations

[sdeepmanav]

Dear VASP Users,
I am facing the problem of slow convergence with respect to the k-point for HF type calculations and it is a really time consuming calculation. Given below is the warning stated in the output file:

"Your generating k-point grid is not commensurate to the symmetry of the lattice. This can cause slow convergence with respect to k-points for HF type calculations .
suggested SOLUTIONS:
1) if not already the case, use automatic k-point generation
2) shift your grid to Gamma (G) (e.g. required for hex or fcc lattice) "

I was wondering which factor makes the calculations very slow if we uses Monkhorst-Pack or Gamma k-points? Can someone explain it and suggest to make the calculations faster as a High-throughput approach? Can we use NKRED=2 in hybrid calculations?

Thanks and regards

Sandeep

[martin.schlipf]

In a high-throughput setting Gamma-centered meshes are definitely more robust than Monkhorst-Pack ones for the reasons mentioned in the warning message. If you get a mesh that is not compatible with the crystal symmetry you need more k-points to recover approximately the correct symmetry of the crystal.

Note that there are other considerations regarding the k-point mesh as well, which depend on the cell size you intend to use. Please read in particular the following section of the wiki regarding the caveats when using NKRED in large cells.

[sdeepmanav]

Thanks Martin for your quick response. Is it possible to convert a Monkhorst-Pack k-points grid into a gamma k-points grid so that we can get the same result? Another question, I was thinking about band structure calculation in VASP with hybrid functions and spin-orbit couplings (SOC)? Is this implemented with all hybrid functions?

Thanks and regards
Sandeep

[martin.schlipf]

Yes for odd grids, the Gamma-centered mesh and the Monkhorst-Pack mesh coincide. See here for more details. However that will not work if you use NKRED.

SOC and hybrid functionals should work.