[gmx-users] center of mass pulling in AFM

[Berk Hess]

>From: Kay Gottschalk <kay.gottschalk at physik.uni-muenchen.de>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>Subject: Re: [gmx-users] center of mass pulling in AFM
>Date: Tue, 18 Jul 2006 12:44:20 +0200
>
>We have a complex with two chains. From one chain (chain A), we are  fixing 
>the COM. We are pulling on the COM of the other chain (chain  B). Now 
>assume that due to interactions with chain B, chain A is  elongated in the 
>direction of pulling. This means that the COM of  chain A has moved in the 
>directions of chain B. To keep the COM of  chain A at the same position, 
>the 'rear end' of chain A has to go in  the opposite direction than the 
>'front end', so that chain A  experiences additional forces and is even 
>more (and now not due to  'real' interactions, but artificially ) elongated 
>due to the COM  fixing. Did I understand that correctly?

Yes.
That's a simple question.
If you keep the COM of a group fixed and part of the group has to
move in one direction, another part of the group will have to
move in another direction.

Berk.