[QE-users] symmetrization of charge density (pw)

[Roland Winkler]

Thank you Pietro for the quick reply.

Sure, the wurtzite structure I am looking at belongs to the hexagonal
crystal system.  So the lattice has point group symmetry D_6h (which
includes space inversion).  But the wurtzite structure (space group 186)
has point group symmetry C_6v (it lacks space invesion).  It is the
latter group that I am refering to and that is correctly used by
sym_rho_init_shells and sym_rho_serial.  The stars are defined for point
group C_6v.  However, after symmetrization, the charge density has point
group symmetry C_3v, i.e., it is not invariant under C_6v.

What am I missing?

Roland


On Fri, Mar 13 2026, Pietro Davide Delugas wrote:
> Hello 
> The stars of G vectors depend on the group with all the symmetries
> of the lattice. The charge symmetrization  is done using the
> symmetries of the crystal structure, i.e. the subgroup of the
> lattice rotations that do not alter the atomic structure. If the
> group and subgroup don' t coincide the charge fourier components do
> not necessarily coincide over the whole shells of G vectors.
> The symmetrization of rho_G is a bit more complicated because for
> each rotation S belonging to the crystal group you need to find  the
> vector G' which is brought to G by S.   
> Pietro