Electrostatic pme/cut-off with zero partial charges

GROMACS version: 2021.4
GROMACS modification: No
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Hi, Groimacs users,
I simulate a polymer system comprising ~18000 atoms. In a system there are bonded (bonds, angles, dihedral and improper) interactions and only van-der-waals non-bonded interactions between atoms considered, and no electrostatic interactions (zero partial charges) taken into account.
When I used in mdp file pme to taken in account electrostatic interactions I got warning
" You are using full electrostatics treatment PME for a system without
This costs a lot of performance for just processing zeros, consider using
Cut-off instead."
However, the performance of simulation with gpu using pme when partial charges are zero is even higher (880 ns/day), as if I use cut-off (660 ns/day) istead pme.
How do you think, is it possible to use pme with zero partial charge to speed up the simulation? Or this simulation when I consider pme without zero partial charges is not the same when the cut-off scheme is used.
Best regards,

Could you post the differences between the two mdp files you used?

Hi, hess!

The difference between two mdp files, please, see below

coulombtype         =  pme; cut-off

Just out of curiousity, is cut-off still slower if you use a small rcoulomb value?