[CP2K-user] [CP2K:18220] MOF cell opt with KEEP_SYMMETRY FALSE

[Corrado Bacchiocchi]

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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