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[lammps-users] Which potential is more reasonable for predicting the crack of graphene during nanoindentation
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[lammps-users] Which potential is more reasonable for predicting the crack of graphene during nanoindentation


From: JWG <w.g.jiang@...127...>
Date: Thu, 22 Jun 2017 14:35:29 +0800 (CST)

Dear all,

Recently I have used different potentials to simulate the nanoindentation of monolayer graphene. The dump files were visualized using Ovito.  When using Tersoff potential (SiC.tersoff), we can obviously observe the crack in the graphene when the indent depth is about 2 nm (similar with the result of Nano letters 2014, 14:7145-7152), but not any cracks when the indentor depth is up to 4 nm when using airebo potential (CH.airebo, pair_style airebo 2.5 0 0). But if I modify  rcmin_CC from 1.7 to 2.0 in CH.airebo, crack can be predicted when the indent depth is about 2 nm  I doubt which potential shall be used in our simulations. 

Another question is that when we use the following sentences to output the Load as a function of indentor displacement,
----
fix 2 all indent 10.0 sphere 50 50 98.20 20.0 units box
fix_modify 2 energy yes
variable depth equal 0.00
minimize 2.3e-16 1.0e-3 200000 200000
variable fload equal f_2[3]*1.6 

----

fix load all print 1 "${depth} ${fload} ${carea}"  file load-area.txt screen no

We found that the curve of load with respect to displacement will not drop to about zero but rise with many drops after the failure of the graphene.  Are there any mistakes in our output for load?
Any comments are appreciated. 
Thanks a lot in advance.

Mike
June 22, 2017