[gmx-users] Ewald summation in 2 dimensions with correction

Dan Gil dan.gil9973 at gmail.com
Sat Nov 11 16:44:20 CET 2017


Hi,

Just wanted to see if anyone had any thoughts...

For more information, if I use:
wall-ewald-zfac = 3
E-z                    = 1 5 0
The electric field from ionic liquid has a magnitude of 7.5 V/nm in the
opposite direction to the applied electric field. This makes no sense to me
at all.

With
wall-ewald-zfac = 5
E-z                    = 1 5 0
The ionic liquid E is -6.2

With
wall-ewald-zfac = 10
E-z                    = 1 5 0
The electric field is still slightly above the expected 5 V/nm.

The dimensions of the box is about 5x5x20 nm3.

Reading various sources say that the wall factor should not matter as long
as it is sufficiently large (x3) but in my case it seems to matter a lot.
Should I report this as a bug or do you think I can investigate this
further?

Best Regards,

Dan

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On Wed, Nov 8, 2017 at 11:37 AM, Dan Gil <dan.gil9973 at gmail.com> wrote:

> Hello,
>
> I am studying room-temperature ionic liquids in slab geometry and I am
> experiencing that I cannot get rid of the interactions between periodic
> images in the z-direction. Is there something wrong with what I am doing or
> is this inevitable?
>
> The reason I think this is because when I change "wall-ewald-zfac" the
> results change also.
>
> Gromacs 5.1
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> ;Integration Method and Parameters
> integrator               = md
> nsteps                   = 4000000
> dt            = 0.002
> nstenergy                = 100
> nstcalcenergy            = 100
> nstlog                   = 5000
>
> ;Output Control
> nstxout = 100
> nstvout = 10000000
>
> ;Cutoff Schemes
> cutoff-scheme            = verlet
> rlist                    = 1.0
> vdw-type                 = cut-off
> rvdw                     = 1.0
> DispCorr                 = EnerPres
>
> ;Coulomb interactions
> coulombtype              = pme
> rcoulomb                 = 1.0
> fourierspacing           = 0.4
>
> ;Constraints
> constraints              = all-bonds
>
> ;Temperature coupling
> gen-vel                  = yes
> tcoupl                   = v-rescale
> tc-grps                  = System
> tau-t                    = 0
> ref-t                    = 300
>
> ;Walls
> pbc                      = xy
> nwall                    = 2
> wall-type                = 10-4
> ewald-geometry           = 3dc
> wall-atomtype            = cp cm
> wall-density             = 5 5
> wall-ewald-zfac          = 10
>
> ;Electric Field
> ;Cosine with freq=0, Field V/nm, Phase=n/a
> E-z                      = 1 0 0
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>
> Best Regards,
>
> Dan
>


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