# [lammps-users] The use of hybrid/overlay in CNTs

Dear All,

I am writing to you to consult you the usage of pair_style hybrid/overlay.

I want to simulate the behaviours of carbon nanotubes (Carbon atoms in the system, and atom style is Charge) with vacancy (some atoms missing).

The potentials are AIREBO and LJ and Coulomb combined by hybrid/overlay.

In our input file, the commands read: (Unit metal)

pair_style hybrid/overlay airebo 3.0 lj/cut/coul/cut 10.0

pair_coeff * * airebo CH.airebo C

pair_coeff * * lj/cut/coul/cut 0.0042038 3.37

The simulation gives me wrong and unreasonable results. The total potential only includes the contribution from lj/cut/coul/cut, but NO AIREBO.

It seems to me that the AIREBO cannot be combined with lj/cut/coul/cut via the command of hybrid/overlay .

Could you kindly help me to sort out this problem?

Thanks a lot.

Best regards

Best regards

Yingyan

School of Engineering,

Building XB 242, Kingswood Campus

University of Western Sydney

Locked Bag 1797, Penrith South DC, NSW 1797

Australia

Tel: 61-2-47360606

Email: yingyan.zhang@…2100…

They can be used together, as you indicate. How do you
know the result is wrong and doesn't include any energy
from AIREBO?

Steve

Dear Steve,

I run 3 simulations to come to the conclusions: the first simulation is using AIREBO (no LJ potential and torsional term, Pair_style airebo 3.0 0.0 0.0). The second simulation use LJ/cut/coul/cut only. The third one use the hybrid/overlay to combine the potentials in the Simulation one and two. The results turn out that the energy in simulation 3 is close to Simulation two.

This problem can be solved by using the following command instead:

pair_style hybrid/overlay airebo 3.0 1.0 1.0 coul/cut 10.0
!!!! (include the LJ potential in first airebo rather than in the second long-ranged potential)
pair_coeff * * airebo CH.airebo C
pair_coeff * * coul/cut

Hope it may help other LAMMPS users,

Best regards
YY

If you're thinking that the LJ term in AIREBO should produce
the same results as the LJ term in pair lj/cut/coul/cut, I don't
think there is any guarantee of that. You'd have to look
carefully to see what pairs are included/excluded with what
weighting factors in the 2 cases. The lj/cut/coul/cut will
exclude nothing, and I'm pretty sure AIREBO will exclude
a lot.

Steve