I am trying to perform EPW calculations on a system that has the following unit cell parameters:

First, I have performed the phonon calculation withibrav = 4 !trigonal symmetry

celldm(1) = 8.02577068

celldm(3) = 2.43976291

**4x4x2 q-point grid**using 'ph.x'.

Then, I have generated

**576 definite kpoints**using the kmesh.pl script fir a

**kpoint grid: 12x12x4**and gave them as input for 'nascf' calculation.

However, when running the nscf calculation with pw.x, it uses

**1005 kpoints**instead due to symmetry issues (I suppose).

Now, it is possible to get around this issue using

But it gives error when running the epw code after using this tag in the nscf calculation.nosym = .true.

On the other hand, the kpoint grid in nscf calculation and the q-point grid for phonon must commensurate (i.e. the k-points must be integer multiple of the corresponding q-points as far as I have understood).

I have tried several combinations of k-point grid for nscf calculations, for some cases, the pw.x runs with specified k-points but involves odd numbered k-point grid (like 13x13x5), but this prohibits to have any other q-point grid than 13x13x5 (which is quite expensive computationally).

I have two quesitons in this regard:

- What could be a systematic approach to resolve this?

- What is meant by uniform k (or q)-point grid in EPW? Does it mean something like axaxa regardless of the crystal system? As the documentation says, for BTE solutions, an uniform grid is needed.

Thanks,

Muhammad Aminul Haque