CHARMM Development Project Forums User Discussion & Questions Energy terms, Constraints, Restraints, and Solvation What command is used to fix angle?

Dear all.
I want to fix angles of between two kinds of molecules (resn X and Y) .
If there are two molecules X (that has atom a and b) and Y (that has atom c).
molecule X ; atom type a, atom type b
molecule Y ; atom type c
I wanna fix angle(a-b-c) to 180.

Is there a command or way to fix like that??

Thank you very much.

There is the CONS IC command (const.info or const.doc) which may work, although a linear angle may be difficult. You would first need to setup an IC table with this angle (intcor.info), e.g.
IC EDIT
ANGLE atom-a atom-b atom-c 180
END