I am modeling a graphene nanosheet under compression loading,so I am using "FIX NVT" for equilibration and then applying load with "SET FORCE" in 3 steps and after each step,running for some time steps. Can I use energy minimization or fix nvt for each step?
Dear Sahar
Using set force command in quasi static condition might be wrong way. Energy minimization is also time consuming. Personally, I prefer doing job with fix deform command added to lammps from 2009. This command will also provide options for relaxation during deformation and constant strain of engineering/true.
Bests
Dear movaffaq
I'm using set force and after each step loading, relax the structure with fix NVT for some time steps,is it wrong in quasi static loading?what's the wrong with using set force in this condition?
Thanks for your attention
Regards
In the force regime the introduced strain in graphene is non-uniform i.e the maximum strain occurs in vicinity of region which force is applied while further part experience lower strains. Thus the determined stress-strain curve would be wrong. In addition, C-C bond strength is ultra sensitive to applied strain. To solve the later problem the best choice is using fix deform as illustrated in prestigious studies by Wei et al. nature materials 11 (2012) 759 ; Grantab et al. Science 330 (2010) 946.
Dear Salah Uddin
Salam
Prestigious user name ;).
Your result, i.e. descending potential energy, is very similar to what obtained in extrusion of oligomers and low molecular weight polymers. In such process, materials are experiencing very high stress in vicinity of a nozzle that cusses deformation and flow-out of the nozzle. Thereafter, the stress almost released.
To ensure your suspicion, I suggest trying fix box/relax at first. This command help you to remove stress from one or more direction before loading. In consequence, you can monitor stress/es during loading. I also suggest to examine uni/biaxial condition to ensure minimizing parameters. However, obtaining an exact parameter for minimize is not an easy task and need much time.
Bests
Dear Movaffaq,
Salam !
Yes, It is. The name is of a great person but I am not the right career of the name :)
Your suggestions are really helpful and I shall try those. I appreciate it.
Have a good one!
Salah Uddin
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