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Re: [lammps-users] About some questions for simulating sliding friction using ReaxFF
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Re: [lammps-users] About some questions for simulating sliding friction using ReaxFF


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Sun, 17 Dec 2017 09:50:01 -0500



On Sun, Dec 17, 2017 at 8:58 AM, 詹胜鹏 <sp_zhan@...414...> wrote:
Dear all, 
      I write a input script of LAMMPS about sliding friction using ReaxFF, the upslab are atoms of iron, and the downslab are atoms of Polyethylene(inclue C and H). some O2 were put into the interface between them. Periodic boundary conditions were applied in both x and y direction,  free boundary condition was applied in z direction. I applied normal force on the upslab in  z direction, then moved the upslab along the x dirction. However, I found that the atoms of upslab go through the downslab. Accroding to my common sense, the atoms of upslab surface contact with the atoms of dowslab surface. I don't know where are wrong for my input script. can you help me and give me some advice. Thank you very much. the part input script and result picture were given the following:

​you are using fix move on the group upslab. that means those atoms are moved according to the parameters with complete disregard of forces. according to *my* common sense, you get exactly what you are asking for.

axel.​

 

units real
neighbor 2.0 bin
neigh_modify every 5 delay 10 check yes
boundary p p s
atom_style charge

read_data LayerFrictionCharge.data
pair_style reax/c lmp_control
pair_coeff       * * ffield.reax.Fe_O_C_H H C O Fe

region down_rigid_layer block INF INF INF INF INF 4 units box
region up_rigid_layer block INF INF INF INF 78 INF units box

group           downRigid region down_rigid_layer
group           upRigid region up_rigid_layer
group boundary union downRigid upRigid
group mobile union upmobile downmobile midslab
group driven union mobile downRigid

compute         newTemp mobile temp
...
...

fix             1 all nve
fix             2 all qeq/reax 1 0.0 10.0 1e-6 param.qeq
fix 3 boundary setforce 0.0 0.0 0.0
fix 4 mobile temp/rescale 10 300.0 300.0 10 1.0
fix_modify 4 temp newTemp

min_style       cg
minimize         1.0e-4 1.0e-6 1000 10000
...
...
...

fix 7 upslab move linear 0.0 0.0 -0.05 units box
timestep 0.1
run 2000

unfix 7
fix 7 upslab move linear -0.05 0.0 0.0 units box
run 17000


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--
Dr. Axel Kohlmeyer  akohlmey@...12...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.