The details are in the article you linked and it will do a much better job
of explaining it than I can.

Let me clarify what I have said in the previous message: Gromacs is using
the correction described in the paper.

On Thu, Feb 8, 2018 at 9:43 AM, Ben Tam <btam...@hotmail.co.uk> wrote:

> Hi Dan,
>
> Thank you for your answer. If gromacs' pbc =xy still calculate periodic in
> the z-direction, how does gromacs take care of the z-direction Ewald?
>
> Best regards,
>
> Ben
> ________________________________
> From: gromacs.org_gmx-users-boun...@maillist.sys.kth.se <
> gromacs.org_gmx-users-boun...@maillist.sys.kth.se> on behalf of Dan Gil <
> dan.gil9...@gmail.com>
> Sent: Tuesday, February 6, 2018 03:49
> To: gmx-us...@gromacs.org
> Cc: gromacs.org_gmx-users@maillist.sys.kth.se
> Subject: Re: [gmx-users] Using xy periodic boundary and 3dc Ewald summation
>
> I believe that the 3DC method still applies summations over Z. From the
> abstract of the paper: "The proposed method adds a correction term to the
> standard Ewald summation formula."
>
> What the 3DC method does is add a correction term so that unrealistic
> electrostatic interactions between periodic images in the Z direction is
> cancelled.
>
> From what I understand, Gromacs' pbc=xy is still periodic in the
> z-direction, hence the zfac option.
>
> Please use Gromacs 2016.4 version and newer, since the devs fixed a bug
> associated with the 3DC method and PME.
>
> Dan
>
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>
> On Mon, Feb 5, 2018 at 11:57 AM, Ben Tam <btam...@hotmail.co.uk> wrote:
>
> > Dear GROMACS user,
> >
> > Currently I am simulating a Metal Organic Frameworks membrane, in which I
> > have applied vacuum space at z direction (3 times of the current
> non-vacuum
> > system). Following the instruction on GROMACS, I have set the pbc = xy
> and
> > ewald-geometry = 3dc. So here is my first question, how does GROMACS
> > calculated the electrostatic potential for z direction when pbc = xy?
> Does
> > it just use Columb's equations?
> >
> > Then following on with my second question. In this paper :
> >
> > http://aip.scitation.org/doi/abs/10.1063/1.479595
> >
> > As far as I understand, 3dc is done by Ewald summation for all xyz
> > direction then a pseudo term is applied to z direction. Then from my
> > understanding is that pbc = xy turn off Ewald summation at z direction,
> > thus how does GROMACS calculated 3dc with z direction periodic boundary
> > turn off (as the pseudo term have to based on full pbc system)?
> >
> > Thank you very much for your help.
> >
> > Best regards,
> >
> > Ben
> > PhD Student
> >
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