[CP2K-user] [CP2K:18225] MOF cell opt with KEEP_SYMMETRY FALSE

[Corrado Bacchiocchi]

 Dear Matthias,
with "KEEP_ANGLES TRUE" the CELL_OPT got completed at the first step, i.e., 
the guess geometry obtained with the preliminary calculation, with KEEP_SYMMETRY 
TRUE, was not further modified.
Again, thank you very much for your kind help
Best
Corrado

On Tuesday, December 20, 2022 at 12:06:52 PM UTC+1 Corrado Bacchiocchi 
wrote:

> yes, the cell remains "Numerically orthorhombic" at all steps (YES at all 
> "CELL| Numerically orthorhombic" lines)
>
> On Tuesday, December 20, 2022 at 12:01:02 PM UTC+1 Matthias Krack wrote:
>
>> Dear Corrado
>>
>>  
>>
>> the CP2K output (e.g. with PRINT_LEVEL medium) informs you if the system 
>> is considered as orthorhombic. Check for the output line:
>>
>> “CELL| Numerically orthorhombic:”
>>
>>  
>>
>> Best
>>
>>  
>>
>> Matthias
>>
>>  
>>
>> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Corrado Bacchiocchi <bac... at gmail.com>
>> *Date: *Tuesday, 20 December 2022 at 11:50
>> *To: *cp2k <cp... at googlegroups.com>
>> *Subject: *Re: [CP2K:18222] MOF cell opt with KEEP_SYMMETRY FALSE
>>
>> Dear Matthias,
>>
>> thanks a lot for the information and the suggestion.
>>
>> Interestingly, the CELL_OPT with KEEP_SYMMETRY FALSE does not change the 
>> angles that remain perfectly at 90 deg at all steps, so, I am afraid that 
>> by applying the constraint KEEP_ANGLES might not going to help in this 
>> case, since they are already not changing, but I will try and let you know. 
>> It might be a useful information to the community.
>>
>> Thanks again!
>>
>> Corrado
>>
>>  
>>
>>  
>>
>> On Tuesday, December 20, 2022 at 11:24:42 AM UTC+1 Matthias Krack wrote:
>>
>> Hi Corrado
>>
>>  
>>
>> CP2K does not take advantage of symmetry for better computational 
>> efficiency. The constraints are rather meant to preserve or enforce a 
>> certain symmetry during structure relaxations, because the symmetric 
>> structure is not the exact minimum or it distorts slightly due to numerical 
>> noise. The latter is the reason why it can make sense to use the constraint 
>> KEEP_ANGLES which will keep all cell angles exactly at 90 degree, because 
>> CP2K/Quickstep is faster for orthorhombic cells. Therefore, based on the 
>> information which you provided for your system, I would apply only the 
>> constraint KEEP_ANGLES in the runs with small molecules adsorbed.
>>
>>  
>>
>> HTH
>>
>>  
>>
>> Matthias
>>
>>  
>>
>> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Corrado Bacchiocchi <bac... at gmail.com>
>> *Date: *Tuesday, 20 December 2022 at 09:54
>> *To: *cp2k <cp... at googlegroups.com>
>> *Subject: *[CP2K:18220] MOF cell opt with KEEP_SYMMETRY FALSE
>>
>> Dear Colleagues,
>>
>> I ask you to kindly share your experience about the following question.
>>
>>  
>>
>> We have performed on our MOF structure the "Converge CUTOFF and 
>> REL_CUTOFF" procedure, as described in the very helpful page:
>>
>>  
>>
>> https://www.cp2k.org/howto:converging_cutoff
>>
>>  
>>
>> and found that, with  NGRIDS 4, to reach a 1.E-7 difference with respect 
>> to the limiting value of the energy, the minimum settings are:
>>
>>       
>>       CUTOFF 1800
>>       REL_CUTOFF 80
>>
>>  
>>
>> We have then successfully performed CELL_OPT on a 2x2x2 supercell of our 
>> MOF with KEEP_SYMMETRY TRUE.
>>
>> When we use this optimized structure for a subsequent CELL_OPT with 
>> KEEP_SYMMETRY FALSE the BFGS algorithm is not able to further decrease the 
>> energy. The structure remains essentially unmodified across hundreds of 
>> steps and the optimization does not complete.
>>
>> I attach the input file and the guess structure and I kindly ask the 
>> following:
>>
>> - is it essential, for any publication quality structure, that 
>> KEEP_SYMMETRY is FALSE or is it acceptable to have this constraint in place?
>>
>> - more in general, for any subsequent calculation, e.g. interaction of 
>> small molecules on the surface of the MOF, Nudged Elastic Band energy path 
>> investigations, etc., is it possible/acceptable to KEEP_SYMMETRY TRUE?
>>
>>  
>>
>> Thank you very much for your kind help
>>
>> Have a nice Holiday Season!
>>
>> Corrado
>>
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