[lammps-users] AIREBO problem for diamond like material simulation during carbon atom deposition

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1

Hi Steve / Lammps Users

I still have a problem with the AIREBO potential for deposition simulation that is bothering me. I have attempted to deposit carbon atoms on a diamond structure. The input files are attached. I have varied the deposition speed, the rate of deposition and the time step. In almost all cases, the temperature blows up after deposition of a few atoms, and the diamond structure "explodes". I have tried similar runs for graphite planes (sp2). While the simulation is slightly more stable (for deposition of 1 atom per 100 steps), this "exploding phenomenon" occurs quite regularly when I choose to deposite 1 atom per 1000 steps instead (less atoms deposited per unit time), something which doesn't seems to make sense.

Steve, I have also tried running the simulation using the script and data file for a small diamond lattice which you sent to me. While for extremely small timesteps (order of 0.1 fs), the simulation works, for more realistic timesteps of (0.5 fs), the diamond lattice explodes after deposition of a few atoms. Also, the diamond lattice also explodes when I use a larger periodic diamond lattice. See attached input and data file.

Has anyone sucessfully perform carbon deposition on a carbon (diamond or graphite) lattice?

Thanks for all your help

Huck Beng

in.swnt_c (1.32 KB)

data.swnt (235 KB)

2

What is a valid timestep for AIREBO? I seem to remember
it being smaller than for other potentials.

Steve

3

Dear all,
although I am not running deposition simulations, my simulations on CNTs and Graphene seems to be fine with 0.8 fs.
Regards,
Vikas

4

Hi Vikas

I agree that for graphene and CNT lammps works fine. However the computation becomes unstable if you perform deposition simulations with graphene or diamond structures.

Thanks

Huck Beng

5

I'd ask Ase Henry (ase at mit.edu) for his thoughts. My only
additional thought is that if you do deposition you'd need
to be very careful not to deposit atoms too close to existing
atoms. Maybe AIREBO is more sensitive to that.

Steve