[Wien] [SPAM?] Re: generate equivalent positions

[Gavin Abo]

FYI, the subprogram that does that is spacegroup (refer to section "9.14 
spacegroup" in the WIEN2k 14.2 usersguide on page 195 [ 
http://www.wien2k.at/reg_user/textbooks/usersguide.pdf ]).

For example, Ti has the nonequivalent position (0,0,0), and it should 
have a Ti equivalent position of (0.5,0.5,0.5), as taken from 
TiO2.struct [ 
https://github.com/hpcugent/easybuild-easyconfigs/blob/master/easybuild/easyconfigs/w/WIEN2k/TiO2.struct 
]:

TiO2
P   LATTICE,NONEQUIV.ATOMS: 2136_P42/mnm
MODE OF CALC=RELA unit=bohr
    8.682000  8.682000  5.592000 90.000000 90.000000 90.000000
ATOM  -1: X=0.00000000 Y=0.00000000 Z=0.00000000 <= Nonequivalent Ti 
position
            MULT= 2          ISPLIT= 8
        -1: X=0.50000000 Y=0.50000000 Z=0.50000000 <= Equivalent Ti position
Ti         NPT=  781  R0=0.00005000 RMT=    2.0000   Z: 22.0
...

Run the WIEN2k spacegroup program in a terminal:

username at computername:~/wiendata/TiO2$ spacegroup
  Type in cell parameters : 8.682000 8.682000 5.592000 90.000000 
90.000000 90.000000
  Type in space group symbol : P42/mnm
  Name of the 1st atom : Ti
  Coordinates of the 1st atom : 0.00000000 0.00000000 0.00000000
  Ti/1        0.00000000  0.00000000  0.00000000
  Ti/2        0.50000000  0.50000000  0.50000000 <= Here, it found the 
equivalent Ti position to be (0.5,0.5,0.5) as expected (for the 2a site 
[ 
http://www.cryst.ehu.es/cgi-bin/cryst/programs//nph-wp-list?gnum=136&what=wpos 
]).
  Name of the 2nd atom :
username at computername:~/wiendata/TiO2$

If you prefer a Windows graphic user interface, there is the EQUIV 
program [ http://www.ccp14.ac.uk/tutorial/lmgp/equiv.htm ].  I believe 
EQUIV might be based on the getspec code [ 
http://www.iucr.org/resources/other-directories/software/getspec ].

I'm not aware of any article describing the insides of the spacegroup 
program or how it was written.  It is likely, though, that the 
"International Tables for Crystallography" [ 
http://dx.doi.org/10.1107/97809553602060000001 ] were used as a reference.

Try searching journals out there related to computational 
crystallography.  For example, the Journal of Applied Crystallography 
might be a good one to search [ 
http://dx.doi.org/10.1107/S0021889875011004 , 
http://dx.doi.org/10.1107/S0021889804031528 ].

On 2/15/2016 7:28 AM, Tomas Kana wrote:
>
> Dear Amir,
>
> At first, you should specify the structure using the Space group number
>
> (for example in w2web or makestruct_lapw). Then, you specify only
>
> one position and the remaining positions (belonging to the space group)
>
> are generated automatically.
>
> Hope this helps
>
> Tomas
>
>
>     Dear WIEN2k users,
>     Please let me know
>     How can i generate equivalent positions for a atom or different
>     atoms  for a compound with a specific symmetry?
>     I would like to know background of it for writing a program.
>     Sincerely,
>     Amir
>
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