[QE-users] Rotated Lattice defined by CELL_PARAMETERS

[Yunzhe Wang]

Dear all,

Purely out of curiosity, I used a rotated simple cubic lattice with one atom at the origin to check the symmetry recognition of pw.x. I've read the trouble shooting section 5.0.0.19: if we rotate C60 molecule in its crystalline form, the symmetry elements of the molecule won't align with these of the underlying lattice, and then these symmetries will be discarded. This is reasonable. But the user guide is a bit ambiguous about the case when the underlying lattices is rotated relative to the Cartesian system.

I tested a little bit. The lattice vectors are specified through CELL_PARAMETERS:
4 0 -3
0 5 0
3 0 4
 This is a cubic lattice tilted a little bit around the v_2 vector (second lattice vector). It turns out only C4_h symmetries with 4-fold axis along v_2 vector are recognized. I attach my input and output for your reference.

So my question is, does pw.x assume that the first principal axis (the symmetry axis of highest order of rotation) of the user-provided CELL_PARAMETERS always align with the z-axis of a global Cartesian coordinate system? An equivalent question is, does the c-vector of the conventional unit cell of the lattice defined by CELL_PARAMETERS always align with z-axis of the Cartesian coordinate system?

Thanks for your patience in reading through this post!

Best,
Yunzhe Wang (Phil)
Mueller Research Group
Johns Hopkins University
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