[Wien] Bi almost cubic

[Peter Blaha]

This is the effect of:


a) a complicated "folding" of the BZ together with a shift of origin.

b) Plot the band structures (use xcrysden in the hexagonal setting to 
get "identical k-mehes".

c) you will see that some bands at some k-points agree, others do not 
and they are very complicated to trace by backfolding.

d) In any case it should become obvious what the DOS at EF looks so 
different. It is most likely a k-mesh problem (you should use enormous 
unshifted meshes), but still, the Tetrahedron method has no problems for 
the DOS at EF in the small one-atom cell since all bands go through EF 
in a straight line and you get a metal.

For the doubled cell, there are many "pseudo gaps" and the Tetrahedron 
method will make a completely different interpolation for the bands and 
if your k-mesh is not VERY dense, give you a semimetal (or "gap").


Otherwise, the results are "identical" as they should, but you have to 
be careful with the interpretation.


> When A is changed to 0.25;
> ----------------
> R LATTICE,NONEQUIV.ATOMS:  1 166_R-3m
> MODE OF CALC=RELA unit=ang
>   8.591340  8.591340 22.415740 90.000000 90.000000120.000000
> ATOM   1: X=0.25000000 Y=0.25000000 Z=0.25000000
> ATOM   1:X= 0.75000000 Y=0.75000000 Z=0.75000000
> Bi         NPT=  781  R0=0.00000500 RMT=    2.5000   Z: 83.000
> -------------------
> sgroup gives this warning;
>
> warning: !!! Unit cell has been reduced.
> sgroup found: 166 (R -3 m)
>
> and the cell is reduced to;
> --------------------
> R   LATTICE,NONEQUIV.ATOMS:  1 166 R-3m
> MODE OF CALC=RELA unit=ang
> 8.591340  8.591340 11.207870 90.000000 90.000000120.000000
> ATOM   1: X=0.00000000 Y=0.00000000 Z=0.00000000
> Bi1      NPT=  781  R0=0.00000500 RMT=    2.5000   Z: 83.0
> ---------------------
> which is "semicubic" with an angle;
>
> Angle is 87.539 deg
> and only one Bi atom in the cell, now in the corners
>
> And in this reduced Bi structure the "gap" at Ef in DOS disappears.
>
> What I see is that with A=0.249 (0.25-0.001) and A=0.2499 (0.25-0.0001)
> the DOS have a "gap" and they are quite symilar, but with the addition 
> of the 0.0001 (A=0.25) the cel is reduced and the "gap" disappears.
>
> I hope that this answers your questions and becomes clear what I am 
> trying to show.
> Saludos
>
> Pablo
> ------------------------------------------------------------------------
>
>
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email:peter.blaha at tuwien.ac.at           
WWW:http://www.imc.tuwien.ac.at       WIEN2k:http://www.wien2k.at
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