I am running a simulation that uses fix shake to constrain bonds and angles of extended spheres of system in 2D, using the atom_style hybrid colloid angle. I am curious if there is a known discontinuity in fix shake when the bond angle is 180 deg. Doing so triggers fix shake to become unstable and it leads to an atom moving too far:
ERROR on proc 6: Shake atoms 15973 15974 15975 missing on proc 6 at step 10
(In 3D the same thing happens but with a shake determinate of 0 error.)
I can also make this error happen when only constraining only the bond distance, but with the initial configuration of the bonds in a 180 deg arrangement (not surprisingly). To get around this (for both cases) I just offset the angle by a degree or two and the constraint is satisfied to satisfaction. Using fix rigid could be a solution, but with a downside that for each angle constraint a new body must be created. I am just curious why this happens. I will attach my script for reference. I am running lammps version 9Feb11.
in_pac.txt (1.43 KB)