Ineffective FIXED_ATOMS constraints in QS MD

Marcella Iannuzzi marci... at
Wed Jan 14 07:34:46 UTC 2015


the MD with constraints works fine for me, in both the NVE and the NVT 
ensemble with a standard thermostat.
The AD_LANGEVIN thermostat gives problems, instead, and it is possibly not 
working properly with such constraints.
Why are you using this thermostat? 
Kind regards

On Tuesday, January 13, 2015 at 5:20:28 PM UTC+1, Marco Caccin wrote:
> Dear all,
> I am trying to run Quickstep MD with some fixed atoms positions (set in 
> MOTION / CONSTRAINT / FIXED_ATOMS), but the positions do change over time.
> Curiously enough, constrained atoms have zero velocity at frame 0 and zero 
> force at every timestep, which would suggest that the constraint is somehow 
> applied but ineffective.
> This behaviour seems to be machine and version independent:
> tested cp2k versions: 2.7 (Development Version) git: 0826abf, 2.6 
> (Development Version) svn:14226, 2.5.1 svn:13632 
> tested architectures/compilers: gfortran 4.8 on Darwin for cp2k 2.7, xlf 
> 14.1 on BlueGene/Q for cp2k 2.5 and 2.6
> The attachments are a minimal example of the problem, showing 5 timesteps 
> of dynamics of 3 atoms of Si of which atom 1 is (or rather, should be) 
> fixed.
> Is this problem known, and is there any workaround? I know there is for 
> GEO_OPT runs as in 
>!topic/cp2k/KAMhME81IbM, but I haven't 
> found anything applicable to MD
> Kindest regards,
> Marco
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