# Electrostatic pme/cut-off with zero partial charges

**URL:** <https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684>\
**Category:** User discussions\
**Tags:** mdp-parameters\
**Created:** [February 17, 2022, 10:03am UTC](https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684 "2022-02-17T10:03:12Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Yel21](https://avatars.discourse-cdn.com/v4/letter/y/b2d939/32.png) [@Yel21](https://gromacs.bioexcel.eu/u/Yel21)\
**Post date:** [February 17, 2022, 10:03am UTC](https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684/1 "2022-02-17T10:03:12Z")

</div>

GROMACS version: 2021.4  
GROMACS modification: No  
Here post your question  
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  
charges.  
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,  
Yel21

---

<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [February 21, 2022, 1:46pm UTC](https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684/2 "2022-02-21T13:46:42Z")

</div>

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

---

<div class="post-metadata">

**Author:** ![Yel21](https://avatars.discourse-cdn.com/v4/letter/y/b2d939/32.png) [@Yel21](https://gromacs.bioexcel.eu/u/Yel21)\
**Post date:** [February 21, 2022, 2:35pm UTC](https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684/3 "2022-02-21T14:35:54Z")

</div>

Hi, hess!

The difference between two mdp files, please, see below

```auto
coulombtype = pme; cut-off

```

---

<div class="post-metadata">

**Author:** ![Braden42](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@Braden42](https://gromacs.bioexcel.eu/u/Braden42)\
**Post date:** [March 1, 2022, 5:52pm UTC](https://gromacs.bioexcel.eu/t/electrostatic-pme-cut-off-with-zero-partial-charges/3684/4 "2022-03-01T17:52:15Z")

</div>

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