[Wien] Modify the supercell-structure file!

[Stefaan Cottenier]

(First of all: your mail was labeled as spam by the spam blocker we 
use here. Maybe some other mailing list readers might have deleted it 
automatically. Your very long added case.struct might have confused 
this spam blocker.)

>           I want to make a 72-atom supercell with 12 unit cells of
> TiO2 where one Ti atom has been replaced by a Cd atom as a
> exercise.Based on the U.G. , we should put the impurity into the
> cell. I do not know how to modify the created supercell-structure 
> file by replacing one atom with an impurity. 

1) increase the number of positions by 1
     
 P   LATTICE,NONEQUIV. ATOMS 25 36_P

2) Take any of the Ti-positions (MULT=n), and make one inequivalent 
position with MULT=n-1 and one with MULT=1 out of it. Change the atome 
of the one with MULT=1 from Ti to Cd. For instance, with this position:

> ATOM   1: X=0.00000000 Y=0.00000000 Z=0.00000000
>           MULT= 2          ISPLIT= 8
> ATOM   1: X=0.25000000 Y=0.25000000 Z=0.16666667
> Ti         NPT=  781  R0=0.00010000 RMT=    1.8000   Z: 22.0
> LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
>                      0.0000000 1.0000000 0.0000000
>                      0.0000000 0.0000000 1.0000000

You make

 ATOM   1: X=0.00000000 Y=0.00000000 Z=0.00000000
           MULT= 1          ISPLIT= 8
 Ti         NPT=  781  R0=0.00010000 RMT=    1.8000   Z: 22.0
 LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                      0.0000000 1.0000000 0.0000000
                      0.0000000 0.0000000 1.0000000
 ATOM   2: X=0.25000000 Y=0.25000000 Z=0.16666667
           MULT= 1          ISPLIT= 8
 Cd         NPT=  781  R0=0.00010000 RMT=    1.8000   Z: 48.0
 LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                      0.0000000 1.0000000 0.0000000
                      0.0000000 0.0000000 1.0000000

(mind the "ATOM=  x"-label, which should be a new, not yet present 
number)

3) Choose a suitable Rmt and R0for your impurity.

4) Go through init_lapw, and accept all changes that nn and sgroup 
propose.

5) You might check visually with xcrysden whether you have obtained 
the desired result.

Stefaan