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

[Pietro Davide Delugas]

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


Il 12 mar 2026 7:21 PM, Roland Winkler <rwinkler at niu.edu> ha scritto:
Dear Users

I am trying to understand how quantum espresso (pw) is symmetrizing
the charge density rhog in reciprocal space.  My understanding is
that for a nonmagnetic symmorphic crystal structure all components
of rhog in a star should be equal [Streitwolf, Group Theory in
Physics, Eq. (6.8)].

For systems with zincblende structure this is, indeed, what I get.
However, for systems with wurtzite structure half of the components
in some stars have opposite signs.

More specifically, I have checked that sym_rho_init_shells
identifies the stars as expected.  However, sym_rho_serial then
gives opposite signs for half of the components in some stars.

The code in sym_rho_init_shells is quite straightforward, using
integer arithmetic for the transformations of the reciprocal lattice
vectors.  This code is doing what I expect, and it gives the results
I expect.  However, I have not yet got the same level of
understanding for sym_rho_serial.  The latter routine is doing
something more complicated, implementing the transformations of the
reciprocal lattice vectors via floating point arithmetic where I do
not understand the reason for this different approach.  I can merely
say that I have instrumented sym_rho_serial to write out the density
after symmetrization and I do not get what I expect as described
above.  [For example, for the job attached below, the components
12,14,16,18,20,22 and 13,15,17,19,21,23 of rhog form two stars
(according to sym_rho_init_shells), but the corresponding values of
rhog in each of these stars are not equal.]

Am I missing something?  Any help is appreciated.

My input file for pw.x is attached.  I am using version 7.5.

Roland Winkler


&CONTROL
  calculation='scf'
  verbosity='high'
  prefix='zns' ! Output files are named according to prefix
/
&SYSTEM
  space_group=186 ! Space group number
  a=3.811  ! Lattice parameter a in angstroms
  c=6.234  ! Lattice parameter c in angstroms
  nat=2    ! Number of atoms in the asymmetric unit
  ntyp=2   ! Number of different atom types. Here, Zn and S.
  ecutwfc=40  ! Kinetic energy cutoff for wavefunctions (Ry)
  ecutrho=200 ! Kinetic energy cutoff for charge density and potential (Ry)
/
&ELECTRONS
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
  Zn 65.38 zn_pbe_v1.uspp.F.UPF
  S  32.065 s_pbe_v1.4.uspp.F.UPF
ATOMIC_POSITIONS crystal_sg
Zn 1/3 2/3 0.00000
S  1/3 2/3 0.38500
K_POINTS automatic
2 2 2  0 0 0
_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu<http://www.max-centre.eu>)
users mailing list users at lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20260313/17979688/attachment.html>