[CP2K-user] [CP2K:13088] Forces in BOMD calculations

Thomas Kühne tku... at gmail.com
Wed Apr 8 18:26:49 UTC 2020

Dear Dmitrii, 

in principle you are obviously right. However, due to the fact that in a numerical calculation the 
number of particles is finite and typically small, the sum of all forces is fluctuating. If everything 
else is correct, the effect is expected to vanish with increasing system size. You can fix the center 
of mass by setting COMVEL_TOL to 0, but in general this is should not be necessary and if so 
likely points to a source of systematic bias in your calculations. 


> Am 08.04.2020 um 19:59 schrieb Dmitrii Nikolaev <dmitrii.... at gmail.com>:
> Dear collegues,
> I am running the Born-Oppenheimer molecular dynamics, and I notice that the sum of the forces on all atoms of my molecule is non-zero. However, as I understand for the NVE ensemble the total force should be zero? What is the reason for this force? 
> Thank you in advance,
> Dmitrii
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Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
tdku... at mail.upb.de

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