[Wien] Rhombhohedral coordinates needed in simulation of LiNiO2

[Gavin Abo]

As far as I know, w2web is not able to automatically detect yet if you 
have entered the atomic positions correctly for space group 166.  So, 
the "positions must be specified in rhombohedral coordinates!" is an 
error message but a reminder text that will always be there whether you 
enter position correctly or incorrectly.  Thus, you have to carefully 
check for yourself that you have entered the position correctly.

As you might recall from the post at [1], WIEN2k is a bit unusual in 
that for the struct file it needs hexagonal lattice constants but 
rhombohedral for the atomic positions for an R lattice space group such 
as 166 R-3m.

For LiNIO2, you should double check, but I believe the both lattice 
constants and atomic positions in the hexagonal setting are:

Initial Setting: R-3m:h (No. 166)

166
5.404616 5.404616 26.569550 90 90 120 <= This is the hexagonal lattice 
parameters needed for the struct file of WIEN2k
3
Li    1    3a    0.000000    0.000000    0.000000 <= These are the 
hexagonal atomic positions, which would be incorrect to use for WIEN2k
Ni    1    3b    0.000000    0.000000    0.500000
O    1    6c    0.000000    0.000000    0.240984

Using SETSTRU [2], its equivalent in the rhombohedral setting should be:


Final Setting: R-3m:r (No. 166)

166 #R-3m:r
9.3901 9.3901 9.3901 33.45 33.45 33.45 <= These are the rhombohedral 
lattice parameters, which would be incorrect to use for WIEN2k
3
Li    1    -    0.000000    0.000000    0.000000 <= These are the 
rhomboderal atomic positions needed for the struct file of WIEN2k
Ni    1    -    0.500000    0.500000    0.500000
O    1    -    0.240984    0.240984    0.240984


In your LiNiO2_opt.struct, I see:

a = 5.404616 bohr in hexagonal setting

b = 5.404616 bohr in hexagonal setting

c = 26.569550 bohr in hexagonal setting

alpha = 90.000000 deg in hexagonal setting

beta = 90.000000 deg in hexagonal setting

beta = 120.000000 deg in hexagonal setting

Li x=0.00000000 y=0.00000000 z=0.00000000 in rhombohedral setting

Ni z=0.50000000 y=0.50000000 z=0.50000000 in rhombohedral setting

O x=0.24098400 y=0.24098400 z=0.24098400 in rhombohedral setting

[1] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg05554.html

[2] https://www.cryst.ehu.es/cryst/setstru.html


On 4/28/2024 8:00 AM, shamik chakrabarti wrote:
> Dear Wien2k users,
>
>            I want to simulate properties of LiNiO2. However, adopting 
> the structure (file attached) by bringing it into rhombohedral axis in 
> Vesta, when I copy the cif file into the working directory & 
> converting it into a struct file, after save structure, it complains 
> about
>
> " positions must be specified in rhombohedral coordinates!"
>
> Please guide.
>
> with regards,
>
> -- 
> Dr. Shamik Chakrabarti
> Research Fellow
> Department of Physics
> Indian Institute of Technology Patna
> Bihta-801103
> Patna
> Bihar, India
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