Question on writing Charmm's input file

From: Ma Chi Chiu <martin$at$yangtze.hku.hk>
Subject: Question on writing Charmm's input file
Date: Wed, 30 Jul 2003 00:51:25 +0800 (HKT)

Dear all,
 My question is how to calculate the force or interaction force with
 CHARMM and how to write the corresponding input file?
 Thank you very much
 yours,
 Martin