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Re: [lammps-users] Different cutoff for hybrid/overly coul/dsf
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Re: [lammps-users] Different cutoff for hybrid/overly coul/dsf


From: Kota Ito <kotaito0@...6521...>
Date: Sun, 9 Jul 2017 07:50:09 +0900 (JST)

Hi Steve and Axel,

Thank you for your kind reply.
I understood that the same cutoff should be used for coul/dsf in general,
but there could be some rooms if I use "individual pair style multiple times"
in hybrid command.
Thank you again for your kind suggestions.

Best regards,
Kota Ito

----- 元のメッセージ -----
差出人: "Axel Kohlmeyer" <akohlmey@...24...>
宛成佈元峡佈: "Kota Ito" <kotaito0@...6521...>
Cc: "lammps-users" <lammps-users@lists.sourceforge.net>
送信済み: 2017年7月7日, 金曜日 午後 11:42:21
件名: Re: [lammps-users] Different cutoff for hybrid/overly coul/dsf

On Thu, Jul 6, 2017 at 7:06 PM, Kota Ito <kotaito0@...6521...> wrote:
> Dear Lammps-Users,
>
> I am now trying to use two cutoffs for "coul/dsf",
> in the framework of "hybrid/overlay".
>
> pair_style hybrid/overlay buck 25.0 coul/dsf 0.1 25.0
> pair_coeff 1 2 buck 18003.7572 0.205205 133.5381 5.0
> pair_coeff 2 2 buck 1388.7730 0.362319 175 25.0
> pair_coeff 1 1 buck 0 0.205205 0 25.0
> pair_coeff 1 2 coul/dsf 5.0
> pair_coeff 2 2 coul/dsf 25.0
> pair_coeff 1 1 coul/dsf 25.0
>
> This gives an error
> "ERROR: Incorrect args for pair coefficients (../pair_coul_dsf.cpp:184)"
> at the position of
> "pair_coeff 1 2 coul/dsf 5.0"
>
> This means that I could set two different cutoffs for "buck",
> but the syntax for "pair_coeff coul/dsf" is somewhat different.

yes, and that is actually documented in the manual.

> I have changed the syntax as
> "pair_coeff 1 2 coul/dsf 0.1 5.0"
> to accept the value of alpha, but the error message is the same.

it is not a good idea to do this. please recall, that coul/dsf is an
approximation to long-range coulomb interactions, only that you don't
have an explicit kspace style.
for that to be consistent, *all* coulomb interactions must have the
*same* damping and the damping determines the cutoff. so the correct
choice here is to define one global cutoff for *all* coulomb
interactions based on the choice of alpha and then just use

pair_coeff * * coul/dsf

axel.

>
> Please help me if you know the solution.
> Thanks in advance.
>
> Kota Ito
>
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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.