LAMMPS WWW Site - LAMMPS Documentation - LAMMPS Mailing List Archives
Re: [lammps-users] 2D graphene simulation
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [lammps-users] 2D graphene simulation


From: Andrew Jewett <jewett@...1937...>
Date: Thu, 19 Oct 2017 11:59:27 -0700

If you want to allow the atoms to move in the x,y,z directions, while
keeping the Z-coordinate of the center of mass of the graphene sheet
at 0, you could try something like

group gGraphene type XXXX # replace with carbon atom type
fix fCen gGraphene recenter NULL NULL 0.0

For details, see
http://lammps.sandia.gov/doc/fix_recenter.html
http://lammps.sandia.gov/doc/group.html

You might also be able to achieve the same thing using fix momentum to
zero the momentum in the z direction, however because this fix does
not operate at every timestep, you might accumulate some slow drift.
You will probably also want to zero the Z component of the velocity at
the beginning of the simulation.

http://lammps.sandia.gov/doc/fix_momentum.html
http://lammps.sandia.gov/doc/fix_velocity.html

Cheers

andrew


On Thu, Oct 19, 2017 at 12:03 AM, Matthew Anthony Xuereb
<matthew.a.xuereb.15@...7179...> wrote:
> Hi,
>
> I am trying to simulate tensile stretching of a small graphene sheet (1000 atoms) with some dislocations generated in it. Current box size is 50 x 50 x 50 Angstroms which is enough to encompass all the atoms. Is there any way to stop the sheet from moving too much in the z-axis? I have tried many boundary styles, namely s and m, and the box always grows 10 times as large during the fix npt run i perform on the box. I do not want to restrict the sheet to a 2D simulation as this will not allow the sheet to ripple during equilibration (which i expect it to do due to the defect). I suspect that the neighbour and neigh_modify commands are the problem.
>
> Below is part of the input file giving me these erroneous results;
>
> units           metal
> dimension       3
> boundary        p       p   s
> atom_style      charge
>
> # ----------------------- ATOM DEFINITION ----------------------------
> read_data defect.data
>
> # ------------------------ FORCE FIELDS ------------------------------
> pair_style      airebo 2.0 1 0
> pair_coeff      * * CH.airebo C
>
> # ------------------------- SETTINGS ---------------------------------
> neighbor 0.5 nsq
> neigh_modify every 5 delay 10 check yes
>
> ######################################
> # EQUILIBRATION
> reset_timestep  0
> timestep 0.001
> fix 3 all box/relax vmax 0.0001 fixedpoint 0 0 0
> velocity all create 300 12345 mom yes rot no
> fix 1 all npt temp 300 300 0.5 x 0 0 0.5 y 0 0 0.5 drag 1
>
> Thanks,
>
> Matthew
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> lammps-users mailing list
> lammps-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/lammps-users