fixing the monolayer graphene

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1

Hello. lammps users.

I simulated the nanoindentation on monolayer graphene.

Monolayer graphene is placed over imaginary circular holes.

And I want that carbon atoms in the outside of circular hole region are fixed to form a rigid boundary.

below is my input scripts. but I do not know how to fix the outside of circular hole region.

Which command is appropriate to use?

Thanks in advance.

dimension 3

boundary p p p

units metal

atom_style atomic

lattice custom 2.53 a1 1 0 0 a2 0 1.732051 0 a3 0 0 1.361789 &

basis 0 0 0 &

basis 0.5 0.5 0 &

basis 0.5 0.16666 0 &

basis 0 0.66666 0

region graphene block -100 100 -100 100 -130 50 units box

create_box 1 graphene

create_atoms 1 region graphene

region up block INF INF INF INF 0.5 INF units box

group slap1 region up

delete_atoms group slap1

region down block INF INF INF INF INF -0.5 units box

group slap2 region down

delete_atoms group slap2

mass 1 12.0

pair_style tersoff

pair_coeff * * SiC.tersoff C

#neighbor 2.0 nsq

#neigh_modify delay 1

fix 1 all nve

compute csym all centro/atom fcc

compute eng all pe/atom

compute eatoms all reduce sum c_eng

thermo 50

thermo_style custom step temp pe ke press pxx pyy pzz lx ly lz

thermo_modify norm no

region fixed cylinder z 0 0 40 INF INF side out units box

group bottom region fixed

fix 8 bottom rigid single

fix 4 bottom setforce 0.0 0.0 0.0 region fixed

dump 2 all custom 500 dump.graphene id type xs ys zs c_csym c_eng fx fy fz

velocity all create 300.0 4928459

fix 3 all temp/rescale 10 300.0 300.0 0.01 1.0

run 10000

------------------------- INDENTATION ---------------------------

timestep 0.001

reset_timestep 0

dump 5 all custom 100 dump.grapheneindent id type xs ys zs c_csym c_eng fx fy fz

variable a equal “5.7-stepdt0.1”

fix 6 all indent 10.0 sphere 0.0 0.0 v_a 5.0 units box

fix_modify 6 energy yes

fix 7 all ave/time 2 5 10 v_a f_6 f_6[1] f_6[2] f_6[3] file graphene.indentation

run 55000

2

Hello. lammps users.

I simulated the nanoindentation on monolayer graphene.

Monolayer graphene is placed over imaginary circular holes.

And I want that carbon atoms in the outside of circular hole region are
fixed to form a rigid boundary.

below is my input scripts. but I do not know how to fix the outside of
circular hole region.

Which command is appropriate to use?

​there are numerous recommendations how to immobilize atoms in the LAMMPS
users mailing list archives. you can exempt those atoms from time
integration or set their velocities and forces to zero.

while digging through the mailing list archives, you should also look for
the many times i have explained why using temp/rescale is a *very* bad
choice.

axel.

3

I would be careful as well with the type of BCs (boundary conditions) you are using and how the penetration depth of the indenter compares to the linear size of the interface. Elastic forces are long-ranged thus you could introduce errors when the pressing too deep while not varying the interface size accordingly. Additionally, notice that you don’t need fixed BCs (unless that is intentionally what you are after) to run a successful indentation test. PBCs will work just fine.

Carlos