# [lammps-users] puzzle about indent simulation

Dear all
I am a new learner of LAMMPS .I want to simulate the process when an AFM diamond tip moving into the surface of AL and forming a hole, i use the EAM and LJ protential in the simulation,and make the diamond rigid and withpout any forces.But when I use VMD to see the outcome, there is something wrong:
(1)in the “in.model”, I made the tip move toward AL, but actually,it not only move but also rotate ,that make me puzzle and don’t kown how to aviod the rotation;
(2)when I clipping the plane in VMD, i found that the two kinds of atom mixed togather(AL and C).And that is not the fact.
(3)at the end of simulation, there is one atom(AL) flies away.
I don’t kown exactly what caused so many problem listed above ,and I hope to get some advice from you !Thanks in advance!

#in.model
units metal
dimension 3
boundary p p s
atom_style atomic
lattice fcc 4.05
pair_style hybrid eam lj/cut 2.5
pair_coeff 1 * lj/cut 1.0 1.0 2.5
pair_coeff 2 2 eam Al_jnp.eam
group AL id > 1658
group C id < 1659
compute new AL temp
velocity AL create 293 45465197 temp new
fix 1 C rigid single
fix 2 C setforce 0 0 0
fix 3 AL nve
fix 4 AL temp/rescale 100 293 293 0.01 1.0
thermo 1000
thermo_modify temp new
dump 1 all xyz 250 lith.xyz
velocity C set 0 0 -1.5 sum no
run 6000

kind regards
GanYang

If you just want to move the C tip into the Al as a rigid body,
I wouldn't use fix rigid. I would just set the force on those
atoms to zero, give them a velocity, and integrate them
with fix nve.

Steve

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