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[Martin Häufel <martin.haeufel@googlemail.com>]

Dear Xavier, dear ABINIT users,

please see attached file (input file). The symmetry group of the output 
crystal structure is:
  space group P-4 m 2 (#115); Bravais tP (primitive tetrag.)

While tetragonal zirconia has space group P4_2/n m c (#137), which was 
used as starting point for the whole optimization.

Best regards,

Martin Haeufel
TU Munich, WSI (T33)
www.wsi.tum.de


On 02.02.2010 17:46, Xavier Gonze wrote:
> On 02 Feb 2010, at 16:43, Martin Haeufel wrote:
> > @Xavier, all ABINIT users: Question
> >
> > There's another thing I would like to point out:
> >
> > If you start with optcell 0 and then continue with optcell 2, you might
> > end up with a different crystal symmetry.
>
> In principle, no ...
>
> > Why is that? Well, in step 1 the structure symmetry might change,
> > because it corresponds to energetically more favourable ionic positions.
>
> In principle no : the symmetries are used to symmetrize the atomic
> positions.
>
> > But in step 2 the symmetry is fixed to the input symmetry, which is now
> > the output of step 1!
> >
> > Is that correct?
>
> If you have observed such a behavior, please could you post your input
> files,
> so that they can be examined ?
>
> Best regards,
> X.

# changed 2010-01-26 11:48h
# TODO find more economical k-point grid
# geometry optimization
# Tetragonal ZrO2 -- Vanderbilt ultrasoft PP
# Dataset 1: ground state calculation, structural optimization of ionic 
#            positions only
# Dataset 2: cell optimization taking symmetry into account
# Dataset 3: calculation of the kss file

ndtset   3

# Definition of the planewave basis set (at convergence ca. 30.0 Hartree)
ecut       40        # Maximal kinetic energy cut-off, in Hartree

pawecutdg  40        # Must be larger or equal to ecut

#xc functional (exchange and correlation)
ixc      2           # 1  LDA or LSD, Teter Pade parametrization
                     #    (4/93, published in S. Goedecker, M. Teter, J. 
Huetter,
                     #    Phys.Rev.B54, 1703 (1996)), which reproduces 
Perdew-Wang
                     #    (which reproduces Ceperley-Alder)
                     # 2  LDA, Perdew-Zunger-Ceperley-Alder (no 
spin-polarization)
                     # 7  LDA or LSD, Perdew-Wang 92 functional

kptopt   1           # Option for the automatic generation of k points
ngkpt    4 4 4       # Density of k points

# Dataset1: usual self-consistent ground-state calculation with optimization 
of
# ionic positions
# Definition of the k-point grid
nkpt1    36
nshiftk1 4
shiftk1  0.5 0.5 0.5 # This grid is the most economical
         0.5 0.0 0.0
         0.0 0.5 0.0
         0.0 0.0 0.5
ionmov1  2           # Conduct structural optimization
optcell1 0           # optimization of the ionic positions only
ecutsm1  0.5         # Energy cutoff smearing
ntime1   200         # number of structural optimization steps
prtden1  1           # print out the density

# Dataset2: self-consistent GS calculation with full optimization of cell 
geometry
# Definition of the k-point grid
nkpt2     39         # A set of 39 k-points containing Gamma
nshiftk2  4
shiftk2  0.0 0.0 0.0 # This grid contains the Gamma point
         0.0 0.5 0.5
         0.5 0.0 0.5
         0.5 0.5 0.0
istwfk2   39*1       # Option needed for Gamma
getcell2  -1
getxred2  -1
ionmov2   2          # Conduct structural optimization
optcell2  2          # full optimization of cell geometry, takes into account 
the
                     # symmetry
ecutsm2   0.5        # Energy cutoff smearing; when optcell/=0, ABINIT 
requires
                     # ecutsm to be larger than zero.
dilatmx   1.1        # maximum dilatation
ntime2    200        # number of structural optimization steps
prtden2   1          # Print out density

# Dataset3: calculation of kss file
# Definition of k-points
nkpt3    39          # A set of 39 k-points containing Gamma
nshiftk3  4
shiftk3  0.0 0.0 0.0 # This grid contains the Gamma point
         0.0 0.5 0.5
         0.5 0.0 0.5
         0.5 0.5 0.0
istwfk3  39*1        # Option needed for Gamma
iscf3     -2         # Non self-consistent calculation
getcell3  -1
getxred3  -1
getden3   -1         # Read previous density file
nband3    50
nbandkss3 100        # Number of bands to store in KSS file
kssform3  3

awtr      0          # no time-reversal symmetry

# Definition of the unit cell
acell  6.762575933123  6.762575933123  9.725221720126  # in Bohr
rprim  1.0  0.0  0.0 # primitive vectors (to be scaled by acell)
       0.0  1.0  0.0
       0.0  0.0  1.0

# Definition of the atom types
ntypat       2       # There are two types of atoms
znucl       8 40     # The keyword "znucl" refers to the atomic number of the
                     # possible type(s) of atom. IMPORTANT: The 
pseudopotential(s)
                     # mentioned in the "files" file must correspond
                     # to the type(s) of atom.

# Definition of the atoms
natom  6             # There are six atoms
typat  1 1 1 1 2 2   # They are of type 1 (oxygen) and of type 2 (zirconium)
xred                 # Reduced coordinates of atoms
      -0.500000000000      0.000000000000      0.205641605764
       0.500000000000      0.000000000000      0.705641605764
       1.000000000000      0.500000000000      0.294358394236
       0.000000000000     -0.500000000000     -0.205641605764
       0.000000000000      0.000000000000      0.500000000000
       0.500000000000      0.500000000000      1.000000000000

# Use only symmorphic operations
symmorphi    0

# Definition of the SCF procedure
nstep        300     # Maximal number of SCF cycles
diemac       20.0    # Although this is not mandatory, it is worth to
                     # precondition the SCF cycle. The model dielectric
                     # function used as the standard preconditioner
                     # is described in the "dielng" input variable section.
tolwfr  1.0d-11
tolmxf  1.0d-10