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From: "htc" <619771202@...1204...>
Date: Wed, 12 Jul 2017 23:28:00 +0800

i have to thank you for your help in the very beginning. I am a new learner of lammps.Without your explain,it may take me more time to know lammps well.

And for the previous question,there still some thing that confuse me.

I use"fix langevin" in "atom_style ellipsoid" before,and in that simulation i use "fix setforce" "fix enforce2d",the system confine in 2d,and operates smoothly.

why things go wrong for rigid body.....

Another question,the command "fix setforce NULL NULL 0",set Fz=0.Does the setting always working during the simulation?i mean,do the command  set Fz to zero during the simlation?The particle only receive the force along x axis and y axis whatever other settings?If so,why i use command"langvein",and "fix setforce" doesnt work?Do the command "fix enforce2d" the same as the command"fix setforce"?

------------------ ???????? ------------------
??????: "Axel Kohlmeyer";<akohlmey@...24...>;
????????: 2017??7??12??(??????) ????9:24
??????: "htc"<619771202@...1204...>;
????: "lammps-users"<lammps-users@lists.sourceforge.net>;
????: Re: [lammps-users] (no subject)

On Wed, Jul 12, 2017 at 4:12 AM, htc <619771202@...1204...> wrote:
> I use this command "fix 1 big rigid/nve/small molecule langevin 1.0 1.0 0.1
> 15346 " to create some rigid bodies,now my purpose is to observe the
> behavior of the rigid body in 2d simulation which means i need to keep
> erasing the Vz Fz of the atoms (or Fz Vz and Tz of the rigid body?It
> confuses me......).

please try without the langevin option.

> I use command "fix setforce"and to make Fz=0,and use "velocity set NULL NULL
> 0 "to make the initial Vz=0.But the rigid body are not confined in 2d,they
> can movitation alone the z dimension.
> And  also  i  found that i can not use the command "fix enforce2d",when i
> use that command the procedure broken.

again, without the langevin option it should work.

> what should i do to reach my purpose?
>
> neigh_modify     exclude    molecule/intra   big
> ERROR: Illegal neigh_modify command (../neighbor.cpp:2058)
> And i dont know why this error arise.

because you are using an old version of LAMMPS but look up the online
documentation. the online documentation *always* reflects the latest
development versions of LAMMPS.
as you can see here: http://lammps.sandia.gov/bug.html development
progresses and with that progress occasional backward incompatible
changes need to be made.

axel.

>
>
> Best
> Tian.
>
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--
Dr. Axel Kohlmeyer  akohlmey@...24...  
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.