From: Wenhao Liu (mdsimulate_at_gmail.com)
Date: Tue Jun 18 2013 - 18:29:38 CDT

Hi vmd people,
I am a little confused about the impropers in NAMD. Is the order of the
improper in parameter file will affect its psi0? Since I read that most of
the impropers in charmm force field use 0 as their psi0, so if the order of
the 4 atoms in improper do affect psi0, then is there rule or clear example
tell me how to deal with this? For example, if I want to restrain four
atoms, A, B, C and D to be in a plane. And these four atoms are bonding
with each other like following:
A B
  \ /
    C
     |
    D
Can I use the order A B C D Kpsi 0 0.000(psi = 0.00) ? Thanks in advance!

Wenhao