The ABINIT Users Mailing List ( CLOSED )

[Stephen Derenzo <sederenzo@lbl.gov>]

Dear ABINIT authors and users

ABINIT is having trouble decoding the conventional unit cell into the primitive unit cell for the following case:

ICSD 31860 is PbBiO2Cl, space group 63 (B m m b), 4 atoms in the irreducible unit cell, 5 atoms in the formula, and Z = 4 gives 20 atoms in the expanded translational unit cell. The ICSD visualizer also shows 20 atoms in the unit cell. There is no obvious internal translational symmetry so it looks like the primitive unit cell has 20 atoms.

My input file defines the unit cell with:

# Definition of the atoms

spgroup 63    # determine conventional unit cell

spgaxor 4    # value from the ABINIT space groups table for 63 B m m b

spgorig 1    # value from the ABINIT space groups table for 63 B m m b

brvltt 6     # value from the ABINIT space groups table for 63 B m m b

natrd 4         # number of atoms in the asymmetric cell

natom 20         # number of atoms in the primitive unit cell

typat  1 2 3 4   # Pb Bi Cl O

xred      # Reduced coordinates of atoms

0           0.25        0.385    

0           0.25        0.09     

0           0.25        0.75     

0.25        0           0        

The job crashes as follows:

gensymspgr : WARNING -

  The assigned brvltt        4 is not equal

  to the input value        6

  Assume experienced user. Execution will continue.

  the choosen orientation corresponds to:  acb

chkprimit : ERROR -

  According to the symmetry finder, the unit cell is

  NOT primitive. The multiplicity is  2 .

  The use of non-primitive unit cells is allowed

  only when the input variable chkprim is 0.

  Action : either change your unit cell (rprim or angdeg),

  or set chkprim to 0.

leave_new : decision taken to exit ...

STOP 1

When I change brvltt to the "assiged value" 4, I get the following:

chkprimit : ERROR -

  According to the symmetry finder, the unit cell is

  NOT primitive. The multiplicity is  2 .

  The use of non-primitive unit cells is allowed

  only when the input variable chkprim is 0.

  Action : either change your unit cell (rprim or angdeg),

  or set chkprim to 0.

leave_new : decision taken to exit ...

STOP 1

If I change brvltt to -1 to get the primitive unit cell, I get the following crash:

abinit : ERROR -

  operat : The number of atoms obtained from symmetries,   8

  is lower than the input number of atoms, natom=     20

  This is not allowed.

  Action : modify natom or the symmetry data in the input file.

leave_new : decision taken to exit ...

STOP 1

The primitive unit cell must have a multiple of 5 atoms. Is this a bug in the unit cell decoding?

Any suggestions?

_______________

Stephen E. Derenzo

Senior Scientist

Lawrence Berkeley National Laboratory

Mail Stop 55-121

Berkeley, CA 94720

(510) 486-4097 (fax 486-4768)

sederenzo@lbl.gov

http://CFI.LBL.Gov