[lammps-users] H2 system

Hello lammps users,

I need to simulate the interaction (physisorption) between H2 molecule and CNTs. I model C-C/C-H/H-H interactions with AIREBO potential.
The problem resides when I try to keep close the H atoms to form the H2 molecule. I know that this force cannot be well modeled with a classical force. I overcame
that problem by using the “rigid” command for each pair of H atom.
Is that method good ?

Any suggestions is highly appreciate.
Thank in advance


If you just have many pairs of H atoms to make rigid as H2 molecules,
then I would use fix shake and not fix rigid. The former will be
more efficient for that purpose. You will need to define a bond
potential that defines the bond length you want.


Dear Steve,
Thanks for your answer. The H atoms are close to form a H2 molecules… but, sometimes, as soon as they approach the CNT walls, the H2 molecules simply disappear. I tried to make smaller the timestep but it does not work.
Does anyone have any ideas?? Thanks a lot again.

2008/11/29 Steve Plimpton <[email protected]>

Why do they disappear? Where do they go? Are they blown
out of the box? You need to figure this out, maybe by doing
viz of your system. I doubt this is a problem with a rigid vs
non-rigid model.


Dear Romano,
Since AIREBO is a dynamic potential, is it possible that the bonds might start broken during the coarse of the simulation and the individual atoms just fly away?