[CP2K-user] [CP2K:17040] Rhombohedral structure optimization (CELL_OPT)

[Tomoki Ogata]

Hi there everyone,

First time posting here, thank you in advance! 
I am trying to do a structural optimization of FAU zeolite, which has a 
rhombohedral unit cell (a = b = c = 17.9 A, alpha = beta = gamma = 60 
degrees). 

I tried running the input file attached, but unfortunately, the 
crystallinity of the structure collapsed. 

[image: structure_collapse.png]

I believe that the reason is related to the line in my input file "SYMMETRY 
RHOMBOHEDRAL", since the structure is preserved if this line is excluded. 
However, without SYMMETRY RHOMBOHEDRAL, the a, b and c parameters of the 
cell deviate from 17.9 A. I looked through the CP2K manual, but was 
unfortunately unable to find any information which might help solve the 
problem.

A part of my input file which is attached:
&CELL
    &CELL_REF
      A 12.6592017 12.6592017 0.0000000 
      B 12.6592017 0.0000000 12.6592017 
      C 0.0000000 12.6592017 12.6592017
      MULTIPLE_UNIT_CELL 1 1 1
      ALPHA_BETA_GAMMA 60 60 60
      SYMMETRY RHOMBOHEDRAL
    &END CELL_REF
    A 12.6592017 12.6592017 0.0000000 
    B 12.6592017 0.0000000 12.6592017 
    C 0.0000000 12.6592017 12.6592017
    MULTIPLE_UNIT_CELL 1 1 1
    ALPHA_BETA_GAMMA 60 60 60
    SYMMETRY RHOMBOHEDRAL
&END CELL

Would anyone happen to know of a way to do a structural optimisation for a 
rhombohedral system while preserving the a, b and c parameters and without 
the structure falling apart?

Thank you in advance,
Tomoki

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