How to move atoms in a group/Help in fix rigid

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1

Dear all,

I am trying to model semicrystalline polymer, which has two crystalline region with amorphous region between them. I want my crystalline regions to behave as a single group and amorphous as other group. So, I have separated them using group command.

During the minimization and equilibration process using lammps, the atoms in the crystalline region should move as a whole instead of individual atoms. That is the crystalline region should follow rigid body motion.
I have tried using fix rigid but on viewing the trajectory, the atoms in the crystalline regions move individually instead as a group. I am not sure whether I can use fix rigid to attain the above motion.

Anyone could please help me out.

Here is the script,

region 1 block -57 23 -235 -115 0 55# crystalline
region 2 block -57 23 120 235 0 55# crystalline
region 3 block -57 23 -115 120 0 55# amorphous

region crystallite union 2 1 2
group amor region 3

group crys1 region crystallite

fix 10 crys1 rigid single

minimization

dump 2 all dcd 100 dump_for_min.dcd
dump_modify 2 unwrap yes
thermo 10
thermo_style custom step pe press vol etotal
min_style cg
minimize 1e-25 0.0 1000000 100000000000
print “MINIMIZATION DONE”
undump 2

write_data aftermin.txt

Thank you,

2

Dear all,

I am trying to model semicrystalline polymer, which has two crystalline
region with amorphous region between them. I want my crystalline regions to
behave as a single group and amorphous as other group. So, I have separated
them using group command.

During the minimization and equilibration process using lammps, the atoms in
the crystalline region should move as a whole instead of individual atoms.
That is the crystalline region should follow rigid body motion.
I have tried using fix rigid but on viewing the trajectory, the atoms in the
crystalline regions move individually instead as a group. I am not sure
whether I can use fix rigid to attain the above motion.

the documentation of the various fix rigid variants explicitly states
that those fixes are *not* invoked during energy minimization.

Anyone could please help me out.

you could experiment with either fix aveforce or do a simulated
annealing MD run to do the minimization.

axel.