[gmx-users] .rtp file - how to define improper dihedrals?

[Dawid das]

Dear Gromacs experts,

Let's say I want to keep in plane such a structure:

          B
           |
          A
        /    \
       C     D

What is the proper order of atoms for CHARMM22 force field in
aminoacids.rtp file under
[ impropers ] section?

Is it:

A C D B  0.0 200.0
?
Does the order or C B and D matter at all? Or the central A atom should be
at the end?

Thank you,

Dawid Grabarek