AMBER Archive (2008)

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

From: Bill K (bill_at_mercury.chem.pitt.edu)
Date: Mon Dec 01 2008 - 12:45:42 CST

Hi Everybody,
     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. Or, perhaps this is
something that has been worked around in the more recent amber
releases. Any input would be greatly appreciated, as I've looked
through the archives on here and haven't seen this discussed before.
Thank you very much for your time and consideration.
    -Bill

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