[gmx-users] how to constrain a dihedral

[mengyi]

Hi all
there are two question:
(1) i want to constrain some dihedrals during MD, 
such as
  1     4
   \    /
   2---3
i want keep [1 2 3 4] planar, how can i do it?

(2) when i use constraints=h-angles, algorithm=shake, it always crash.
 but if i use constraints=h-bonds there is no problem. why? is there something
need to do before using angle-constraint?

thanking you all in advance





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