Symmetry was not retained during cell-varied geometry optimization of an iodine single crystal (Space Group #64 - Cmce, 8 atoms in unit cell) with primitive cell (4 atoms). No matter we set "KEEP_SPACE_GROUP" and "KEEP_SYMMETRY" to be T or F, with or without set "SYMMETRY" to be "ORTHORHOMBIC" or even "MONOCLINIC_GAMMA_AB Monoclinic (a = b ≠ c, α = β = 90°, γ ≠ 90°)" (as it is in
https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/SUBSYS/CELL/CELL_REF.html) in $CELL, the symmetry was not maintained and became monoclinic or triclinic where it can't recognize the structure as a primitive cell of C-centered orthorhombic lattice any more.
My question: In cp2k, must we not use primitive cell for cell-varied structural optimization or am I too naive to set correct parameters to retain symmetry?
I've searched Google and conversations in cp2k group and didn't find relevant contents. Any help would be appreciated. Thanks!
PS: Original Cell information:
&CELL
A [angstrom] 3.
7632537052 -2.2808521645 0.0000000000
B [angstrom] 3.
7632537052 2.2808521645 0.0000000000
C [angstrom] 0.0000000000 0.0000000000 9.7061460000
PERIODIC XYZ
SYMMETRY MONOCLINIC_GAMMA_AB
&END CELL
&COORD
I 0.0000000000 0.
7474991182 1.1868772390
I 0.0000000000 3.
8142052109 8.
5192687610 I -0.0000000000
1.5333530464 6.0399502390
I 0.0000000000 3.0283512827 3.6661957610
&END COORD
Methods:
Functional: PBE + DFT-D3(BJ)
Basis sets: DZVP-MOLOPT-SR-GTH
K-points: 8,8,3
CUTOFF and rel-CUTOFF: 400,50
EPS_SCF: 1E-6
EPS_DEFAULT: 1E-12