I constantly get this error message. when I visualize the output, I realize the O-H bond has extended far away even though I add the fix shake.
The fix command I used was:
fix OH_bond all shake 0.0001 20 0 b 7
The explanation from the LAMMPS manual was:
The determinant of the quadratic equation being solved for a single cluster specified by the fix shake
command is numerically suspect. LAMMPS will set it to 0.0 and continue.
But I still don’t know how to prevent this from happening. Any suggestion will be highly appreciated.
the O-H bond has extended far away even though I add the fix shake.
What do you mean by this statement? If you mean the bond is stretching
far, then that is happening in a single timestep due to huge forces. And
SHAKE is having a difficult time restoring the bond length, leading
to numerical difficulties. SHAKE should only be used as a modest
restoring force. So you need to figure out why your system is trying
to pull apart one or more of these bonds.
One good test is that you should be able to run your
system without fix SHAKE and have it stay nice
and stable and be in equilibrium. If you can't do that,
then turning SHAKE on is just putting lipstick on a pig.