EPW Forum

Hi,
I am performing an electron-phonon calculation in EPW 6.1. During the calculation I encounter the following error:
{Error in routine ktokpmq (1):
coarse k-mesh needs to be strictly positive in 1st BZ}
My current coarse grids are,
nk1 = 12
nk2 = 12
nk3 = 12

nq1 = 6
nq2 = 6
nq3 = 6
The 12×12×12 k-grid is commensurate with the 6×6×6 q-grid. I understand from the ktokpmq routine that EPW requires the coarse k-points to be represented with positive crystal coordinates within the first Brillouin zone, i.e. in the range [0,1). therefore generated the 12×12×12 k-point mesh using the Wannier90 kmesh.pl utility uniformly. However, I still encounter the same ktokpmq error in EPW. Please find the attachment.
Looking forward your responses.
Thanks!
Akshay Kumar Majee,
NISER Bhubaneswar, India

Hello Akshay,

This issue appears when you use more cores (npool) than total number of k-points, 1728 in your case. It can also appear if you use SCF wavefunctions within the 1st BZ for the EPW calculation instead of NSCF wavefunctions on a uniform grid.

Best regards,
Sabya.