Question About CNT Collapsing during Metal Deposition

Hi,

I am currently modeling the deposition of metal clusters on a single-walled carbon nanotube. After a large amount of cluster impacts (~20), the tube begins to collapse inward so that the cross sectional area of the tube is an ellipse rather than a circle. When this happens, the clusters fail to deposit on the “bent” outer area of the tube, but form a coating everywhere else.

Is there a way to prevent this from happening via a relaxation strategy? I don’t want to treat the tube as an explicitly rigid or undeformable body.

The first part of my code follows. If I should provide anything else for clarity, I would be happy to.

Thanks,

Alex

#----------Sim Parameters-------------
units metal
dimension 3
boundary p p p
atom_style atomic
variable latparam equal 3.52
newton on
#----------CNT Creation---------------
read_data input.atoms

region CNT block 0 40 0 40 0 50 units lattice
group CNT region CNT

Potentials

pair_style hybrid airebo 3.0 eam/alloy morse 3.0
pair_coeff * * airebo CH.airebo C NULL
pair_coeff * * eam/alloy Ni99.eam.alloy NULL Ni
pair_coeff 1 2 morse 0.234 1.975 2.27 3.0

mass 1 12.0111
mass 2 58.6934

minimize 1.0e-15 1.0e-15 10000 10000
min_style cg

dump 65 all xyz 100 dump.xyz

reset_timestep 0
timestep 0.001
velocity all create 300 12345 mom yes rot no

fix 1 all nvt temp 300 300 100

fix 2 CNT momentum 10 linear 1 1 1

fix 3 CNT momentum 10 angular

thermo 20
thermo_style custom step temp
run 1000
unfix 1

-------------Cluster Deposition-------------

reset_timestep 0
fix 1 all npt temp 300 300 1 z 0 0 100 drag 1

region C1 block -1.76 1.76 10 11.76 0 48 units box
lattice fcc ${latparam} orient x 1 1 0 orient y -1 1 0 orient z 0 0 1
create_atoms 2 region C1
group C1 region C1
velocity C1 set 0 -0.8 0
run 1500

#---------More clusters deposited in same fashion----------

Non-coated region.png

Hi,

I am currently modeling the deposition of metal clusters on a
single-walled carbon nanotube. After a large amount of cluster impacts
(~20), the tube begins to collapse inward so that the cross sectional area
of the tube is an ellipse rather than a circle. When this happens, the
clusters fail to deposit on the "bent" outer area of the tube, but form a
coating everywhere else.

Is there a way to prevent this from happening via a relaxation strategy? I
don't want to treat the tube as an explicitly rigid or undeformable body.

​alex,

you are getting a result that is the consequence of the physics of the
model that you are using and i believe you are asking the wrong question
here.

the first question should be: is this actually what is happening in real
life? or in other words, how do you know that what you are seeing is not
what should happen?
and the second question - in case the answer to the first is "no, this
should not happen" - would be: how can you improve the model? which part is
not representing the real physics accurately enough?

any other kind of tinkering - making the CNT rigid is only an extreme form
- will take your simulation from doing science to creating an animation.

now, you have to realize that using a mechanical force field
coupling/mixing like you are doing, is a rather coarse approximation of the
underlying real physics. each segment is using a model that doesn't really
"know" about the other part. it can only "feel" their forces coupled via
the morse potential.

so ultimately, what you should be doing next is essentially a validation,
that the model you are using is sufficiently accurate for the process you
are studying, and if not, what other model (potential?) is available that
has a better description of the actual physical behavior?, or how can you
improve the parameters? or is there a parameterization that can correctly
describe - in the same potential parameter set - a CNT, nickel metal layers
and CNT-Nickel composites?

axel.

Non-coated region.png

Axel,

I see your point. As always, I really appreciate your input. I’ll do my due diligence and see where I can get with this.

Best,

Alex

Non-coated region.png