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[verstraete@pcpm.ucl.ac.be]

If you want a hexagonal cell set angdeg 90 90 120. It is impossible for 
abinit to find an orthorhombic cell if your angles are this way.

What you could also be lacking (your input file was incompletely cited - 
give us the whole thing!) is natrd and spgroup. If you want it to complete 
the atoms by symmetry (if there are more than 4 of them in the unit cell) 
abinit has to know what the space group is, and natom is the total 
(reducible) number of atoms. natrd is then the irreducible number of 
atoms (4).

Matthieu



On Wed, 3 Nov 2004, Marcos Verissimo Alves wrote:

> 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

--
===================================================================
Matthieu Verstraete               mailto:verstraete@pcpm.ucl.ac.be 
PCPM, Boltzmann, pl. Croix du Sud, 1            tel: 010/ 47 33 59
B-1348 Louvain-la-Neuve  Belgium                fax: 010/ 47 34 52