AMBER Archive (2008)

Subject: Re: AMBER: How do you evaluate forces on a fixed atom?

From: David A. Case (case_at_biomaps.rutgers.edu)
Date: Tue Dec 02 2008 - 08:39:37 CST

On Mon, Dec 01, 2008, Bill K wrote:

> Has anyone tried to extract the systematic forces on a fixed
> atom, or may know how to do it? I'm using amber7 and, if you have an
> atom fixed in the system, the forces on it are canceled before they
> can be evaluated. That is to say, output prints values of 0.0 0.0 0.0
> for the force on a fixed atom, even though it experienced forces from
> the surrounding atoms. Looking at the code, this occurs because
> ibelly sets these values to zero. It looks like this task is not
> possible without changing the source code.

I agree: you would have modify the code to print out the forces before the
ibelly step sets them to zero. I'm pretty sure this has not changed in more
recent releasees.

...dac

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