Dear LAMMPS users,
Question: The system I want to simulate is to compress a rigid body system in 2d. In my system, the rigid particle is an ellipsoid with several spheres on its surface. When I run the simulation, I find the rigid particle still have z-direction translation and rotation around x/y-axis even though I use fix enforce2d and fix rigid torque * off off on. Though the translation and rotation is small in the small size system. But when I increase the particle number (e.g. number of ellipsoids = 5000), the rotation around x/y will become obvious that can be seen using my eyes in compressing. How can I fix this problem?
LAMMPS version: 2 Aug 2023
Operating system: Rocky Linux release 8.7 (Green Obsidian)
in script:
variable ellipse_a equal 3.8
variable ellipse_b equal 1.0
variable ellipse_c equal 1.0
variable sphere_d equal 0.4
units lj
atom_style hybrid molecular ellipsoid
dimension 2
read_data 50.data
set type 1 mass 1.0
set type 1 shape 3.8 1.0 1.0
set type 2 mass 1.0
set type 2 shape 0.4 0.4 0.4
group big type 1
group small type 2
pair_style gayberne 1.0 1.0 1.0 5
pair_coeff 1 1 1.0 1.0 1 1 1 1 1 1
pair_coeff 1 2 1.0 1.0 1 1 1 1 1 1
pair_coeff 2 2 1.0 0.4 1 1 1 1 1 1
neighbor 0.5 bin
neigh_modify delay 0 every 1 check yes
fix 1 all rigid/npt molecule temp 1.0 1.0 1.0 iso 0 10 1 torque * off off on force * on on off
fix 2 all enforce2d
neigh_modify exclude molecule/intra all
compute mytemp all temp/asphere
compute mypressure all pressure mytemp
fix_modify 1 temp mytemp press mypressure bodyforces early
compute 0 all property/atom quatw quati quatj quatk shapex shapey shapez
dump 1 big custom 2000 dump.ellipse.compress id type x y z c_0[*]
dump_modify 1 colname c_0[1] quatw colname c_0[2] quati colname c_0[3] quatj colname c_0[4] quatk &
colname c_0[5] shapex colname c_0[6] shapey colname c_0[7] shapez sort id
thermo_style custom step temp epair etotal press
thermo_modify temp mytemp press mypressure
thermo 2000
timestep 0.005
run 20000
write_data compress.data
data file: