Null Velocity in Z direction while equilibration of Graphene

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1

I was performing equilibration (NPT, NVT and NVE) of a Graphene sheet of a specific length.

After completion of NPT, I was checking the velocities by dumping files (the command highlighted in the input script below). I checked that my Vz component of the velocities are coming zero. Its true that this is the component perpendicular to the plane of graphene sheet (x-y), but I dont understand why LAMMPS is showing the Z- component of velocities to be zero. The error is constant for other lengths too.

Can anyone please advise me on that and make suggestions on how to rectify my input script to get correct results. I have attached all the inputs below. Thanks a lot.

The sample input script pasted here is :

# Fixing NPT, NVT, NVE in Graphene

dimension 3
units metal
atom_style atomic
read_data data.graphene50
pair_style tersoff
pair_coeff * * SiC.tersoff C
group Carbon type 1

thermo 1

thermo_style custom step temp epair etotal press vol
minimize 1.0e-7 1.0e-9 0.1 1000
fix 1 Carbon npt temp 300.0 300.0 0.1 iso 0.0 0.0 1
thermo 50
timestep 0.001
dump 1 Carbon atom 100 dump.atom

dump 2 all custom 100 dump.snap.*.cfg id type x y z vx vy vz
run 5000000
unfix 1
fix 2 Carbon nvt temp 300.0 300.0 0.1

run 5000000
unfix 2
write_restart equil.restartG501

fix 3 all nve

run 2000000
unfix 3
write_restart equil.restartG502

in.graphene (707 Bytes)

SiC.tersoff (1.53 KB)

data.graphene50 (330 KB)

2

Replies below.

Ray

[...]

The sample input script pasted here is :

# Fixing NPT, NVT, NVE in Graphene

dimension 3
units metal
atom_style atomic
read_data data.graphene50
pair_style tersoff
pair_coeff * * SiC.tersoff C
group Carbon type 1

thermo 1
thermo_style custom step temp epair etotal press vol
minimize 1.0e-7 1.0e-9 0.1 1000

The third argument "maxiter" must be an integer. 0.1 does not work.

If you add even the smallest initial velocity to the atoms by
"velocity all create 0.1 ANYSEED", you will see VXs are not zero
anymore. This has to do with your graphene sheet lying perfectly on
the x-y plane at its equilibrium with no initial velocity.

fix 1 Carbon npt temp 300.0 300.0 0.1 iso 0.0 0.0 1
thermo 50
timestep 0.001
dump 1 Carbon atom 100 dump.atom

dump 2 all custom 100 dump.snap.*.cfg id type x y z vx vy vz

I assume the intention was to dump cfg files for AtomEye, however this
will not work.

Ray