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Re: [lammps-users] slab correction in PPPM/disp and Ewald/disp
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Re: [lammps-users] slab correction in PPPM/disp and Ewald/disp


From: "reza N.Z" <mrn.nz91@...24...>
Date: Tue, 24 Oct 2017 11:37:59 +0330

>>that is not what i am saying. the slab correction applies to the
>>*residual* dipole of the entire system.

So, the system should be entirely neutral. 

>>i don't understand what you are asking here. please elaborate in more
>>detail and quote the particular sections to the manual you are
>>referring to.

In the lammps documentation on the following page: 
http://lammps.sandia.gov/doc/kspace_modify.html
on the last line of the paragraph which the slab keyword is introduced, this sentence was added;" The slab option is also extended to non-neutral systems (Ballenegger)."

Actually I am looking for a way to use PPPM/disp or Ewald/disp method for a 2 dimensional system and it is important to cancel both Lenard-Jones and Coulombic long-range interactions across the non-periodic direction. Could you give a suggestion? 



On Thu, Oct 19, 2017 at 5:22 PM, Axel Kohlmeyer <akohlmey@...24...> wrote:
On Thu, Oct 19, 2017 at 5:42 AM, reza N.Z <mrn.nz91@...24...> wrote:
> Thank you so much Axel
>
>>the slab correction is for coulomb only and only cancels inter-slab
>>interactions of the residual dipole moment across the slab.
>
> You mean that Coulombic interaction of Ions wont be canceled across the
> slab?

that is not what i am saying. the slab correction applies to the
*residual* dipole of the entire system.

> Actually, I am confused by your _expression_ and the Lammps
> documentation where the kspace_modify is introduced, it is stated that slab
> correction is extended to non-neutral systems.
> Could you explain how the modification changes the Yeh slab-correction?

i don't understand what you are asking here. please elaborate in more
detail and quote the particular sections to the manual you are
referring to.

any periodic system with a non-neutral cell has essentially a
diverging energy. all reciprocal space based long-range solvers work
around this by ignoring the divergent (k=0) term. this applies to slab
systems as well. if you had a residual non-zero charge, the slabs
would repel each other, but since you have the same repulsive force in
positive and negative directions, it will cancel.

axel.

>
> Thank you so much for your precious guides.
> Best regards
> Reza
>
> On Tue, Oct 17, 2017 at 11:38 PM, Axel Kohlmeyer <akohlmey@...24...> wrote:
>>
>> On Tue, Oct 17, 2017 at 1:16 PM, reza N.Z <mrn.nz91@...24...> wrote:
>> > Dear lammps Users
>> >
>> > As I concerned by reading the documentation, the slab correction is
>> > performed to constrain the Coulombic long-range interaction in one
>> > direction
>> > (as performed in Yeh and Berkowitz work).
>> > I wonder If the slab-correction removes both Coulombic and Lenard-Jones
>> > dispersion interactions in PPPM/disp or Ewald/disp method?
>>
>> the slab correction is for coulomb only and only cancels inter-slab
>> interactions of the residual dipole moment across the slab.
>>
>> axel.
>>
>> > I will appreciate any comments.
>> >
>> > Best regards,
>> > Reza
>> >
>> >
>> >
>> >
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>> >
>>
>>
>>
>> --
>> Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
>> College of Science & Technology, Temple University, Philadelphia PA, USA
>> International Centre for Theoretical Physics, Trieste. Italy.
>
>



--
Dr. Axel Kohlmeyer  akohlmey@...43...4...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.