ABINIT Discussion Forums

Hello,
I am trying to make same calculations (fist only the total energy) about spinel type structures (Prototype: Al2MgO4 (Spinel)
Pearson Symbol: cF56, pace Group: Fd3m , Number: 227) and I took from http://cst-www.nrl.navy.mil/lattice/struk/h1_1.html the primitive atoms (for the case SnMg2O4 where u = 0.375 see "First-principles study of cation distribution in eighteen closed-shell...spinel oxides" Su-Huai Wei and S. B. Zhang PHYSICAL REVIEW B, VOLUME 63, 045112).
This link I quoted has 14 entries as basis/primitive atoms (that I typed with great care in the input). I did not set chkprim to 0 because I believed that I did right; nevertheless I found the following typical error
chkprimit : ERROR -
According to the symmetry finder, the unit cell is
NOT primitive. The multiplicity is 4 .
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.

Can anyone help me with how to write well the primitive unit cell in the case of spinels??
Thanks in advance

What did you use for acell and rprim? For this structure you should have
acell 3*8.0788 angstrom
rprim 0 1/2 1/2
1/2 0 1/2
1/2 1/2 0

I did use that acell and rprim, my question was focussed on about xred because, as I said, writing down 14 entries as especied in ttp://cst-www.nrl.navy.mil/lattice/struk/h1_1.html does not work. Taking another spinel example (cobalt ferrite: Fe2O4Co), I found a .cif that only specifies 3 asymetric atoms and used the brvltt -1 option nevertheless I found the same error. So I wonder what xred to write and other options (like spgaxor, spgorig , brvltt) have to write in the input file so not to meet with this error. I have to add that I also wrote "spgroup 227" in the input file

jzwanzig wrote:What did you use for acell and rprim? For this structure you should have h
acell 3*8.0788 angstrom
rprim 0 1/2 1/2
1/2 0 1/2
1/2 1/2 0

Hi, see the following input, it works--


[code] #Common input variables
spgroup 227

#Definition of the unit cell
acell 3*8.0806 angstrom
brvltt -1

# kspace grid
kptopt 1
kptrlatt 4 4 -4
-4 4 -4
-4 4 4

#Definition of the atom types
ntypat 3
znucl 13 12 8 # Al Mg O

#Definition of the atoms
natom 14 #
natrd 3
typat 1 2 3

xred
3*5/8
3*0
3*0.3873

nstep 50
occopt 1[/code]

That seemed to work fine, thanks for the help