Airebo Potential for high temperature > 3000 K

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1

Hi,

I’m trying to generate a stress-strain curve for a single layer of graphene sheet
at high temperatures.

I’m using a time step of 0.5fs and periodic boundary condition in all directions.

Since I’m simulating for single layer of graphene, i considering only the REBO

part by turning off the LJ and torsion term.

I want to equilibrate the system at 3300 K and 0.0 bar. So I used NPT ensemble

for equilibration. But it doesn’t works. “The simulation box size increases tremendously”.
I tried to control it by using different damping factor. But it is of no use.

The input script which I followed till 2400 K works fine. Compared with the results from

“Temperature and Strain-rate dependent fracture strength of graphene” , H.Zhao and N.R.Aluru,

Journal of Applied physics.

  1. fix 1 all npt temp 3300.0 3300.0 0.05 iso 0.0 0.0 0.5 drag 1.0

or

  1. fix 1 all langevin 3300.0 3300.0 0.05 12345
    fix 2 all press/berendsen iso 0.0 0.0 1000.0 dilate partial

I tried the combination of langevin thermostat and berendsen barostat. Still i can’t able to

control the box dimension.

My question is:

  1. were these fixes (like Nose-hoover, langevin or berendsen) can be able to

simulate high temperature cases.

  1. Or there is some problem with REBO potential in simulating higher temperature cases?

I’m asking this because the sublimation/melting temperature of the graphene is above

4000 K.

Thanks in advance,

Ramki

2

Hi,

I'm trying to generate a stress-strain curve for a single layer of graphene
sheet
at high temperatures.

I'm using a time step of 0.5fs and periodic boundary condition in all
directions.
Since I'm simulating for single layer of graphene, i considering only the
REBO
part by turning off the LJ and torsion term.

I want to equilibrate the system at 3300 K and 0.0 bar. So I used NPT
ensemble
for equilibration. But it doesn't works. "The simulation box size increases
tremendously".
I tried to control it by using different damping factor. But it is of no
use.

The input script which I followed till 2400 K works fine. Compared with the
results from

"Temperature and Strain-rate dependent fracture strength of graphene" ,
H.Zhao and N.R.Aluru,
Journal of Applied physics.

1. fix 1 all npt temp 3300.0 3300.0 0.05 iso 0.0 0.0 0.5 drag 1.0

                          or

2. fix 1 all langevin 3300.0 3300.0 0.05 12345
    fix 2 all press/berendsen iso 0.0 0.0 1000.0 dilate partial

I tried the combination of langevin thermostat and berendsen barostat. Still
i can't able to
control the box dimension.

My question is:

1. were these fixes (like Nose-hoover, langevin or berendsen) can be able to
simulate high temperature cases.

There is no limitation on these fixes.

I would increase the temperature of the system in a more gradual way
rather than shooting it to 3300K instantly. E.g.

fix 1 all nve
fix 2 all langevin 300.0 3300.0 0.1 SEED
fix 3 all press/berendsen ...

Ray