[CP2K-user] [CP2K:20180] Different Total energy and ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]

[Benjamin Shi]

Hi Jurg,

Thank you very much for the information. Just to confirm, the "Total 
FORCE_EVAL (QS) energy" quantity is the correct energy to use?

For this calculation, I have used an EPS_SCF of 5E-7, which is tighter than 
default. Are you suggesting that the discrepancy between "Total energy:" 
and "Total FORCE_EVAL (QS) energy" which I'm observing here means that my 
forces could be noisy or energy isn't well-converged? Previously, I have 
confirmed that the force is well-converged by modifying/increasing 
EPS_DEFAULT and it changes atomic forces by less than 0.01 eV/A.

Best wishes,
Benjamin

On Monday, May 6, 2024 at 5:34:01 PM UTC+10 Jürg Hutter wrote:

> Hi
>
> this is a problem of consistency of forces and energies. During the SCF
> some energy terms (especially with diagonalization) are calculated from the
> input density and some from the output density. Upon convergence
> the energy is recalculated in a consistent manner and forces are wrt this
> energy.
> However, this shouldn't matter as long as the density is sufficiently 
> converged.
> In your case I would suggest to improve SCF convergence, as that will also
> considerably reduce the noise (or error) on your forces (good for ML).
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
> Benjamin Shi <benjam... at gmail.com>
> Sent: Sunday, May 5, 2024 11:56 AM
> To: cp2k
> Subject: [CP2K:20171] Different Total energy and ENERGY| Total FORCE_EVAL 
> ( QS ) energy [a.u.]
>
> Dear CP2K developers,
>
> I am writing to enquire as to what the difference is between the energy 
> given by "Total energy:" and "ENERGY| Total FORCE_EVAL ( QS ) energy 
> [a.u.]:". As seen in attached output file, I'm finding a slight difference 
> in the two energy values. Does this arise because I incorporate Fermi 
> smearing? In the context of training machine learning potentials, which 
> quantity would be the correct quantity to use that is consistent with the 
> forces that are printed out?
>
> Thank you for your help,
> Benjamin
>
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