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[lammps-users] Particle repulsion for random distribution
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[lammps-users] Particle repulsion for random distribution


From: "Roberts, Andrew" <A.P.Roberts@...5884...>
Date: Wed, 14 Jun 2017 16:44:44 +0000

Hello,


I've successfully generated 650 spheres at random positions within a flow region, whilst maintaining the walls in fixed positions. Initially (1.png) the particles overlap, but after the first timestep (2.png), the particles get thrown out beyond the walls (my script is attached as in.flowrandomrelax.couette).


I have tried to modify the approach using the micelle tutorial. The spheres I have generated are monodisperse, and it is possible to fit 650 spheres into the region size using a square lattice with a zero separation. Reducing the number of spheres doesn't remove the problem, nor does reducing the A-factor in the soft pair style.


I created the spheres randomly:

   create_atoms 1 random 650 90210 region_flow    


I set the pair style to soft - I set a zero cutoff because I expect the separation to be negative. When the separation is zero I don't want any repulsion, but I do want repulsion when the separation is negative (is that possible?). I also set the A factor to be small so the repulsion is small.

   pair_style soft 0.0

   pair_coeff * * 0.0 0.01


I also ramped the A factor from zero to 0.01

   variable prefactor equal ramp(0,0.01)

   fix 3 all adapt 1 pair soft a * * v_prefactor


I wondered if you know the cause of the excessive repulsion?


Kind regards,


Andrew


Attachment: 1.png
Description: 1.png

Attachment: 2.png
Description: 2.png

Attachment: in.flowrandomrelax.couette
Description: in.flowrandomrelax.couette