[lammps-users] Problem with energy minimization in Graphere sheer

Hi All,

I need to get an equilibrated graphene structure.
For this first I have created a 2D configuration of C atoms in the hexagonal lattice and tried to minimize the energy. I am using AIREBO potential.
Ideally I should get a perfect planar structure.
But when I use the initial coordinates such that the “z coordinate is constant”, I find that lammps is throwing an error message sayiing “Cannot use neighbor bins - box size << cutoff”.
If I perturb the z coordinate randomly by a small amount, the minimization proceeds. I want to know why it happens like that.

The second problem is, lammps doesn’t change the box boundaries while minimization. Hence I wanted to know the ideal lattice parameter by running the minimization for various lattice parameters and getting the energy. I find that when I increase the lattice parameter more than 10% of equilibrium value, the energy remains constant wrt lattice parameter though I am well with the cut-off. Also in the final configuration I see the atoms moving up and down in the z-direction which are not supposed to move.

Please help me in figuring our where I am doing a mistake.

Thank you,


If you're running a 2d problem, you need to use "dimension 2".
See the howto doc pages on 2d problems. If you run 3d and have
an epsilon size of your system in z, then you can't use neighbor bins
b/c the box is epsilon in size.