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[Marcos Verissimo Alves <verissim@df.ufscar.br>]

Hi all,

I am performing some calculations now for a second allotropic form of
BaO. A paper by Weir, Vohra and Ruoff (PRB 33, 4221, yr. 1986) states
that this form has a hexagonal unit cell belonging to the space group
$P6_3/mmc$. When I feed the fractional coordinates of the atoms as
supplied in the paper, the symmetry analysis of abinit gives me another
space group, Pmma, orthorombic. Here is my input:

#Definition of the unit cell
acell      3.8   3.8   6.6

angdeg     90.0     90.0    60.0

#Definition of the atom types
ntypat 2         # There are two types of atoms
znucl 8  56


#Definition of the atoms
natom 4
typat 1 1 2 2
xred
    0.0   0.0   0.0             # Oxygen
    0.0   0.0   1/2             # Oxygen
    2/3   1/3   1/4             # Barium
    1/3   2/3   3/4             # Barium

and here is abinis' output:

 ingeo : use angdeg to generate rprim.
 ingeo : takes atomic coordinates from input array xred

 symanal : COMMENT -
  The Bravais lattice determined only from the primitive
  vectors, bravais(1)=  6, is more symmetric
  than the real one, iholohedry=  3, obtained by taking into
  account the atomic positions.
 symspgr : the symmetry operation no.   1 is the identity
 symspgr : the symmetry operation no.   2 is an inversion
 symplanes : the symmetry operation no.   3 is a mirror plane
 symaxes : the symmetry operation no.   4 is a 2-axis
 symaxes : the symmetry operation no.   5 is a 2_1-axis
 symplanes : the symmetry operation no.   6 is a mirror plane
 symplanes : the symmetry operation no.   7 is an a,b, or c plane
 symaxes : the symmetry operation no.   8 is a 2-axis
 symspgr : spgroup=  51  Pm m a   (=D2h^5)
 getkgrid : length of smallest supercell vector (bohr)=    3.800000E+00
       Simple Lattice Grid
 symkpt : found identity, with number  1
 invars1: mkmem  undefined in the input file. Use default mkmem  = nkpt
 invars1: With nkpt_me=    1 and mkmem  =     1, ground state wf handled
in core.
 invars1: mkqmem undefined in the input file. Use default mkqmem = nkpt
 invars1: With nkpt_me=    1 and mkqmem =     1, ground state wf handled
in core.
 invars1: mk1mem undefined in the input file. Use default mk1mem = nkpt
 invars1: With nkpt_me=    1 and mk1mem =     1, ground state wf handled
in core.

 Symmetries : space group Pm m a (# 51); Bravais oP (primitive ortho.)
 getkgrid : length of smallest supercell vector (bohr)=    3.800000E+00
       Simple Lattice Grid
 symkpt : found identity, with number  1

Any hints?

Thanks,

Marcos

-- 
Dr. Marcos Veríssimo Alves
Departamento de Física
Universidade Federal de São Carlos
São Carlos, SP - Brasil
***********************************
Dr. Marcos Verissimo Alves
Physics Department
Universidade Federal de Sao Carlos
Sao Carlos, SP - Brazil