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<div dir="auto">Hello
<div dir="auto">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.</div>
<div dir="auto">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. </div>
<div dir="auto">Pietro</div>
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<div class="elided-text">Il 12 mar 2026 7:21 PM, Roland Winkler <rwinkler@niu.edu> ha scritto:<br type="attribution">
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<div>Dear Users<br>
<br>
I am trying to understand how quantum espresso (pw) is symmetrizing<br>
the charge density rhog in reciprocal space. My understanding is<br>
that for a nonmagnetic symmorphic crystal structure all components<br>
of rhog in a star should be equal [Streitwolf, Group Theory in<br>
Physics, Eq. (6.8)].<br>
<br>
For systems with zincblende structure this is, indeed, what I get.<br>
However, for systems with wurtzite structure half of the components<br>
in some stars have opposite signs.<br>
<br>
More specifically, I have checked that sym_rho_init_shells<br>
identifies the stars as expected. However, sym_rho_serial then<br>
gives opposite signs for half of the components in some stars.<br>
<br>
The code in sym_rho_init_shells is quite straightforward, using<br>
integer arithmetic for the transformations of the reciprocal lattice<br>
vectors. This code is doing what I expect, and it gives the results<br>
I expect. However, I have not yet got the same level of<br>
understanding for sym_rho_serial. The latter routine is doing<br>
something more complicated, implementing the transformations of the<br>
reciprocal lattice vectors via floating point arithmetic where I do<br>
not understand the reason for this different approach. I can merely<br>
say that I have instrumented sym_rho_serial to write out the density<br>
after symmetrization and I do not get what I expect as described<br>
above. [For example, for the job attached below, the components<br>
12,14,16,18,20,22 and 13,15,17,19,21,23 of rhog form two stars<br>
(according to sym_rho_init_shells), but the corresponding values of<br>
rhog in each of these stars are not equal.]<br>
<br>
Am I missing something? Any help is appreciated.<br>
<br>
My input file for pw.x is attached. I am using version 7.5.<br>
<br>
Roland Winkler<br>
<br>
<br>
&CONTROL<br>
calculation='scf'<br>
verbosity='high'<br>
prefix='zns' ! Output files are named according to prefix<br>
/<br>
&SYSTEM<br>
space_group=186 ! Space group number<br>
a=3.811 ! Lattice parameter a in angstroms<br>
c=6.234 ! Lattice parameter c in angstroms<br>
nat=2 ! Number of atoms in the asymmetric unit<br>
ntyp=2 ! Number of different atom types. Here, Zn and S.<br>
ecutwfc=40 ! Kinetic energy cutoff for wavefunctions (Ry)<br>
ecutrho=200 ! Kinetic energy cutoff for charge density and potential (Ry)<br>
/<br>
&ELECTRONS<br>
/<br>
&IONS<br>
/<br>
&CELL<br>
/<br>
ATOMIC_SPECIES<br>
Zn 65.38 zn_pbe_v1.uspp.F.UPF<br>
S 32.065 s_pbe_v1.4.uspp.F.UPF<br>
ATOMIC_POSITIONS crystal_sg<br>
Zn 1/3 2/3 0.00000<br>
S 1/3 2/3 0.38500<br>
K_POINTS automatic <br>
2 2 2 0 0 0 <br>
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