[CP2K-user] [CP2K:21469] EPS_DEFAULT Meaning

[Robert Molt]

Thank you so much! This answer is very helpful and appreciated, Marcella.

On Wednesday, May 14, 2025 at 10:45:49 AM UTC-4 Marcella Iannuzzi wrote:

> Dear ?
>
> As you might have noticed, the EPS_DEFAULT is in a section of the input, 
> the QS section, where several other EPS_* are present.  
> Some of these can be controlled all at once by setting EPS_DEFAULT. 
> Setting them individually overwrites the eps_default derived value.
> Some more details on the meaning of each of them can be revealed by their 
> description. 
> If you have still doubts on what they refer to, you might have a look at 
> the original QS papers.
> Using default values for all of them is in  general a good choice, if you 
> do not have a reason for doing otherwise. 
>
>
> EPS_SCF,  as other  "accuracy control parameters", is  instead not 
> controlled by EPS_DEFAULT
> The exact meaning of EPS_SCF depends on the optimisation method in use, 
> but it is not the energy convergence, 
> With OT it can be considered as the maximin gradient.
>
> Regards
> Marcella
>  
>
> On Wednesday, May 14, 2025 at 4:36:20 PM UTC+2 rwmo... at gmail.com wrote:
>
>> 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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>>>
>>

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