[CP2K-user] [CP2K:21478] The total force calculated by CP2K is not zero

[liu dongfei]

Thanks for your reply!
The attached file is the result of a calculation, showing that the total 
force of the system is :
-------------------------------------------------------
....
    189      2      H          -0.02270940    -0.01715719    -0.01124088
    190      2      H          -0.00819690     0.01778486    -0.00220956
    191      2      H          -0.00491958    -0.00982567     0.00540266
    192      2      H          -0.00744376     0.00269638    -0.00803075
 SUM OF ATOMIC FORCES           0.00405273    -0.00782982     0.01173920   
  0.01468126
-------------------------------------------------------
The total force here is not particularly small, and it is comparable to the 
forces experienced by some H atoms. 
Is this result reasonable, even considering the ripple effect?

best wishes,

Dongfei

On Monday, 19 May 2025 at 21:26:00 UTC+8 Jürg Hutter wrote:

> Hi
>
> inaccurate numerics can be a source for forces not summing up to zero. 
> However, I assume
> (we don't know actually, as you don't share the forces) that the residual 
> force is due to the
> 'ripple effect'. CP2K uses aequidistant grids to calculate XC energies. 
> For such grids there is no
> longer any translational invariance.
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of liu 
> dongfei <liud... at gmail.com>
> Sent: Monday, May 19, 2025 5:00 AM
> To: cp2k
> Subject: [CP2K:21474] The total force calculated by CP2K is not zero
>
> Hi all, I’m currently simulating a pure water system with CP2K. Despite 
> configuring appropriate convergence criteria (e.g., CUTOFF, REL_CUTOFF, and 
> EPS_SCF), the total forces from the calculation do not converge to zero. 
> Attached is my input configuration.
> Could anyone provide insights into potential causes or recommend 
> literature discussing this specific issue?
> Thanks in advance!
>
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