From: Swamy Sumanth (
Date: Mon Dec 14 2015 - 23:59:25 CST

   I am Ch.Swamy pursuing my M.Tech at IIT Guwahati. I was working with
CHARMM force field for simulating ionic liquids. I have one doubt regarding
impropers in CHARMM format. Suppose an improper set in the parameter file
 was like CT-CS-NI-OA, then according to OPLS format atom type NI was
central atom of this set of improper i.e; 3rd position in the set, while
coming to set of impropers given by command "topo guess improper" in VMD
what exactly the atom sequence is i.e; position of central atom in the set?

With regards,
Dept. of chemical,
IIT Guwahati.