# [Ifeffit] space group 224 & Atoms

Robert Gordon ragordon at alumni.sfu.ca
Sun Oct 22 02:50:18 CDT 2017

```Hi,

I was trying to simulate Cu2O...cubic...O tetrahedrally coordinated by
Cu...Cu linearly coordinated by O.
There are two origin choices for space group 224 (Pn-3m).
If using origin choice 1, then atom positions would be
O    0,0,0
Cu  0.25,0.25,0.25
If using origin choice 2, translate by -0.25,-0.25,-0.25 to get
O  0.75,0.75,0.75
Cu  0,0,0
(or use the shift vector in Atoms...)

My understanding is that Demeter defaults to the 2nd origin choice.

Problem I am having is that neither gives me linearly coordinated copper
using current Atoms.
If I read in the attached atoms.inp (choice 2) and Run Atoms, the ATOMS
list in the
Feff output begins with:

ATOMS                  * this list contains 87 atoms
*   x          y          z     ipot tag           distance
0.00000    0.00000    0.00000  0  cu1           0.00000
-1.06675    1.06675    1.06675  2  o1.1          1.84767
-1.06675   -1.06675    1.06675  2  o1.1          1.84767
1.06675    1.06675   -1.06675  2  o1.1          1.84767
-1.06675   -1.06675   -1.06675  2  o1.1          1.84767
2.13350    2.13350    0.00000  1  cu1.1         3.01722

I get 4-coordinate instead of 2-coordinate.
If I try origin choice 1, almost the same result....

ATOMS                  * this list contains 83 atoms
*   x          y          z     ipot tag           distance
0.00000    0.00000    0.00000  0  cu1           0.00000
-1.06675    1.06675    1.06675  2  o1.1          1.84767
1.06675   -1.06675    1.06675  2  o1.1          1.84767
1.06675    1.06675   -1.06675  2  o1.1          1.84767
-1.06675   -1.06675   -1.06675  2  o1.1          1.84767
2.13350    2.13350    0.00000  1  cu1.1         3.01722

If I run choice 1 with the shift vector, I do reproduce the choice 2 result.

If I use the old dos version of Atoms with origin choice 2,
I do get linearly coordinated copper:

ATOMS
.00000      .00000      .00000    0   cu1               .00000
-1.06675    -1.06675    -1.06675    1   o1               1.84767
1.06675     1.06675     1.06675    1   o1               1.84767
.00000    -2.13350     2.13350    2   cu1              3.01722

SPECS:

Demeter 0.9.26 (pre2)
Win10x64
AMD64

-R.

-------------- next part --------------
## This Atoms file was generated by Demeter 0.9.26
## Demeter written by and copyright (c) Bruce Ravel, 2006-2017

title = Cuprite
space = 224
a     =   4.26700    b    =   4.26700    c     =   4.26700
alpha =  90.00000    beta =  90.00000    gamma =  90.00000
rmax  =   6.00000    core  = cu1
polarization = 0.0  0.0  0.0
shift =     0.00000    0.00000    0.00000
atoms
# el.     x           y           z        tag
Cu     0.00000     0.00000     0.00000   cu1
O      0.75000     0.75000     0.75000   o1
```