[gmx-users] Negative AFM forces??

[Berk Hess]

>From: George Patargias DPhil <GEORGEP at biop.ox.ac.uk>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] Negative AFM forces??
>Date: Tue, 29 Nov 2005 15:55:32 +0000
>
>
>Hello
>
>I am sorry to bother everybody for this.
>
>Thanks Berk for your previous answer about the AFM forces.
>What is still not clear about the AFM pulling forces is
>this: If the force exerted on the pulled group is indeed
>F = k*(z_spring - z_pullgroup) then why do I get negative
>forces? Does this mean that pulled group can overcome the
>spring???

If z_pullgroup > z_spring then F is negative.
The force always pulls the group back to z_spring,
which could be up or down depending on where the group is.

Berk.