[CP2K-user] [CP2K:21466] EPS_DEFAULT Meaning

[Robert Molt]

I believe you are invoking that "epsilon" is often used as a *symbol* for a 
tolerance in numerical work. That is not my question. I am asking for the 
mathematical definition being invoked here; it is a control parameter *for 
what*? I am guessing that this is a control parameter for the SCF energy?

EPS_SCF appears in a different CP2K manual and has the definition "Target 
accuracy for the SCF convergence" This is a somewhat unclear definition, 
but given that it has a default threshold of 10**-5, I will assume it is 
stating that the largest matrix element difference between iterations must 
be no bigger than the threshold, since that is the usual criterion (as 
opposed to converged energy or converged eigenvalues).

Is EPS_DEFAULT overriding EPS_SCF values to govern convergence? Assuming 
that "epsilon" here is a numerical tolerance for an SCF, what specific 
element of the SCF process is it managing?

On Wednesday, May 14, 2025 at 8:51:12 AM UTC-4 Krack Matthias wrote:

> “eps” is a short for “epsilon” and refers to a threshold value which 
> controls the numerical accuracy.
>
>  
>
> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
> Robert Molt <rwmo... at gmail.com>
> *Date: *Wednesday, 14 May 2025 at 14:29
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *Re: [CP2K:21464] EPS_DEFAULT Meaning
>
> I already cited the manual in my question. I do not know what "eps" is. 
> The manual does not seem to say it, as far as I can see. I want to guess 
> that this is referring to the eigenvalues of the Fock matrix, but this is 
> not directly stated. Can this be defined relative to somehting in SCF 
> theory? I want to guess that this puts a tolerance on eigenvalues, but then 
> this would seemingly be redundant to having an EPS_SCF keyword? If this is 
> different than EPS_SCF, can the definition be given?
>
> On Wednesday, May 14, 2025 at 8:00:32 AM UTC-4 Krack Matthias wrote:
>
> Hi
>
>  
>
> Open the CP2K input reference 
>
>
> https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/QS.html#CP2K_INPUT.FORCE_EVAL.DFT.QS.EPS_DEFAULT
>
> in your browser and search/find all occurrences of “EPS_DEFAULT”. 
> EPS_DEFAULT defines the default values for all EPS_xxx keywords referring 
> to EPS_DEFAULT in their description.
>
>  
>
> Alternatively, you can consult the source code:
>
> https://github.com/cp2k/cp2k/blob/master/src/cp_control_utils.F - L837-L858 
> <https://github.com/cp2k/cp2k/blob/master/src/cp_control_utils.F#L837-L858>
>
>  
>
> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
> Robert Molt <rwmo... at gmail.com>
> *Date: *Wednesday, 14 May 2025 at 13:32
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *[CP2K:21462] EPS_DEFAULT Meaning
>
> Good morning,
>
>  
>
> Can someone clarify the EPS_DEFAULT keyword? The manual is unclear. It 
> states:
>
> "Try setting all EPS_xxx to values leading to an energy correct up to 
> EPS_DEFAULT"
>
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