[QE-users] Correct symmetry setup NaCl

[Ian Dunn]

Hi folks,

I'm trying to setup first an SCF calculation and eventually a band structure and relaxation calculation of a system with a NaCl-like lattice. Right now I have an input file with 64 atoms in a cube shape, which corresponds to 8 unit cells of the NaCl crystal structure. I've specified the CELL_PARAMETERS as well as the atomic coordinates and chosen ibrav = 0. I'm getting the following warning:

Message from routine setup:
     using ibrav=0 with symmetry is DISCOURAGED, use correct ibrav instead


  1.  What is the correct solution for setting up my supercell; should I be using ibrav = 1 instead and specifying the vectors for repeating my super cell?
  2.  For my own understanding, what is the issue with using symmetry with ibrav=0? By symmetry am I correct to assume that this warning is referring to symmetry detection within the supercell? If so, how does specifying ibrav=1 help with symmetry detection?
  3.  For what it's worth, it looks like symmetry detection is occurring at some level since the code output "Found identity + (  0.0000  0.2500  0.2500) symmetry". However, I would expect to also see (0.25, 0, 0.25) and (0.25, 0, 0.25) as symmetry operations for an NaCl structure so perhaps there is a problem here after all. Am I understanding correctly?

Best regards,
Ian Dunn (he/him)
ASML Wilton MDEV Analysis Architect

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