Peter,
That is what the cutoff is. I guess steve or someone in his team can talk about this in a more detailed way.
P.S. I had a couple of email communications with Prof. S. J. Stuart (who is one of the author of AIREBO potential) and he actually believed that an arbitrary shorter cutoff should not be an appropriate choice. The only rationale I can see behind using shorter cutoff is that the simulated critical failure strain/stress seems to be larger than the experimental results. However, there is little “direct” experimental data that is reliable.
Best regards,
AC
In general, all of the params for a complex manybody potential
like AIREBO are fit together, so changing something like one
of the cutoff terms is not a good idea.
Also want to say that this thread is a great example of various
experts weighing in on a question to provide advice to
LAMMPS users - lots of good technical leads in this one.
Steve
Steve,
I agree with you one hundred percent. Especially for complicated potential like REBO/AIREBO, just changing one cutoff could induce spurious effects, especially when one is talking about the fracture behavior involving bond breaking.
Just for the record, I’m attaching my input script and configuration files (5.5deg zigzag GB) for the community to test, including both original REBO potential and modified AIREBO potential (both rcmin_cc=1.92 A or rcmax_cc= 1.92 A) as the Science paper suggested. For those who are interested in verifying the debated results, please go ahead to test and let me know your results.
Here is the conversion of stress-strain curve:
strain = (timestep-5000)0.40.0005/160 (engineering strain)
stress(t) = A(t)-176.17300.4778.78/(160154*3.4)/10000 (GPa) (minus sign is for tensile stress), assuming graphene thickness being 0.34 nm, where A(t) are the second column values in the stress.all file. This formula is to use the correct/actual volume rather than the simulation cell volume.
Thanks a lot.
AC
CH.airebo.m (905 KB)
in.tensile.vel.airebo (1.44 KB)
in.tensile.vel.REBO (1.44 KB)
Zigzag_GB_5.5deg.atoms (441 KB)