problem with minimization and calculation of force on a fixed atom

From: Ben Adams (
Date: Thu Aug 31 2017 - 17:03:21 CDT

Dear NAMD users,

I want to calculate forces on a few constrained atoms while I'm doing
merely energy minimization. I used colvars with harmonic restraints and
obtained force based on the distance of the atom of interest to a specified
Center value. But the minimization causes dramatic fluctuations on
calculation of force. Changing the force constant, minimization options
mentioned in tutorial don't help that much. and the results are not even
An alternative way would be to freeze that atom and calculate the force
directly. But using the 'fixedAtoms' option leaves the force at the atom
equal to zero and do not allow to extract its value.
Is there any other way to freeze an atom while the force on it is being
Or is there anyway to make minimization more stable when a colvar
constraint is present?

Thanks in advance,

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