Basic question about impropers

From: Wenhao Liu (
Date: Tue Jun 18 2013 - 18:30:12 CDT

Hi namd 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:
  \ /
Can I use the order A B C D Kpsi 0 0.000(psi = 0.00) ? Thanks in advance!


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