Plumed and Constrained Atoms

Frank von Horsten xxx.f... at
Fri Mar 13 10:57:06 UTC 2015

Dear All,

I have a question regarding constrained atoms in combination with 
metadynamics using plumed.

I have a small system in which I want to constrain some atoms. This works 
as expected when I run the calculation without plumed.
However, with plumed turned on, one of the constrained atoms starts moving. 
The only difference is that this atom is part of the collective variable 
CV, which is defined as the distance between that atom and another 
unconstrained one.
A look on the forces shows that these are not zero for the constrained 
atom, which is part of the CV when plumed is on.

So the question is, whether the constraints are not applied to atoms, which 
are part of the CV? Or in other words: is this a bug or a feature?

I tested this for CP2K 2.5.1 + plumed 1.3 and one of the latest SVN 
versions + plumed 2.1.1. Also it happens for FIST and QUICKSTEP.

Thanks and best wishes
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