improper torsion

From: Hidekazu WATANABE (evergreen_tow_at_yahoo.co.jp)
Date: Fri May 18 2007 - 04:56:37 CDT

Hi, everybody.

I'd like to ask the potential of the improper torsion.
The potential function of the improper is
V(improper) = Kpsi(psi - psi0)^2 in NAMD parameter file.
How to define the angle psi in V(improper) = Kpsi(psi - psi0)^2,
in the case of 4 atoms A, B, C, and D forming following structure?

             C
A - B <
             D

Is psi defined as the dihedral angle between ABC and ABD plains,
or as the angle between bond AB and BCD plane?

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