Constraint violated by particle

[Ahmad Reza Motezakker]

Dear All, 

I have a system of a polymer chain, LB fluid and wall constraints (a small chain of polymer, Two wall for fluid boundary and at the same place two wall constraints for setting up the wall-particle interaction). I make the system in the order of creating the polymer chain, fluid and its LB boundaries (Wall), and constraints. I do not face any error during polymer warming up, equilibration, and fluid-polymer warming up. I define the polymer far from the constraints and add lennard-jones repulsion between the polymer and constraints to avoid any constraint violation. I define the LB boundaries and constraints as follows:

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logging.info("Setup LB boundaries.")

top_wall = espressomd.lbboundaries.LBBoundary(shape=espressomd.shapes.Wall(normal=[0, 0, -1], dist=0))

bottom_wall = espressomd.lbboundaries.LBBoundary(shape=espressomd.shapes.Wall(normal=[0, 0, 1], dist=50))

system.lbboundaries.add(top_wall)

system.lbboundaries.add(bottom_wall)

#for constraints only

TopWall = Wall(dist=0, normal = (0,0,-1))

BottomWall = Wall(dist = 50, normal=(0,0,1))

system.constraints.add(shape = TopWall, particle_type = 10, penetrable=False)

system.constraints.add(shape = BottomWall, particle_type = 10, penetrable=False)

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But when I run the integration, in the very very first step (while the polymer is the middle of the box and far from the walls) I face the error : Constraint violated by particle.

Could you please give me some hints on that? I really appreciate your help.

​Best Regards,

Ahmad Reza