[CP2K-user] [CP2K:21480] The total force calculated by CP2K is not zero

[liu dongfei]

Thank you for your detailed and professional response. I understand now!
This computational result was obtained when I was investigating the 
performance of different k-point calculation settings. 
In principle, the gamma point calculation setting is reasonable for this 
system.

best wishes,
Dongfei

On Monday, 19 May 2025 at 22:53:17 UTC+8 Jürg Hutter wrote:

> Hi
>
> These are the total forces for 64 waters from the ripples.
> (BTW no k-points here, but why do you have a 3 3 1 grid?)
>
> GPW PBE 0.011
> GPW LDA 0.002
> GAPW PBE 0.002
> GAPW LDA 0.0001
>
> Keep in mind that these forces are correct forces for the energy 
> functional defined in CP2K.
>
> 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 4:28 PM
> To: cp2k
> Subject: Re: [CP2K:21478] The total force calculated by CP2K is not zero
>
> 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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