[Wien] Fwd: band structure dependence on symmetry and complex calculation

[Peter Blaha]

There is no automatic way to do the "unfolding".

However, if you are interested only in 2 bands, you can do this by hand.

Maybe you get already the solution from the irreducible representations, 
but then you have to understand group theory and sub/supergroup relations.

A more direct way is plotting the wavefunctions (lapw7, switch off 
APW+lo for this analysis) for one eigenvalue after the other and 
remember what "gamma" or "X" means in terms of a "Bloch state".

A "original Gamma" point will have the same phase (sign of the 
wavefunction) in all "original unit cells";
a "original X-point" (which is now of course also at gamma) will have 
different phases in the first or second "original" unit cell.

To make this more clear a simple 1D-example of a 1D H-atom chain with 
one atom/cell.

The ground state at Gamma looks like (plotting 4 unit cells):

|  |  |  |  |  |
  +  +  +  +  +

the ground state at "X"  has a phase factor exp(2pi/a*0.5 *r).
Its wave function looks therefore like:

  +  -  +  -  +

Now double the cell in this direction (2 H atoms/cell). You will now 
find 2 bands at Gamma, but there wavefunctions will look like above and 
thus you "know" that the second eigenvalue is the "backfolded X-point".




On 07/02/2013 10:16 AM, venkatesh chandragiri wrote:
> Dear sir,
> i have not get any comments on my previous mail. So, forwarding the same
> for your reference.
>
> regards,
>
> venkatesh.
>
> ---------- Forwarded message ----------
> From: *venkatesh chandragiri* <venkyphysicsiitm at gmail.com
> <mailto:venkyphysicsiitm at gmail.com>>
> Date: Sun, Jun 30, 2013 at 12:22 AM
> Subject: Re: [Wien] band structure dependence on symmetry and complex
> calculation
> To: wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>
>
>
> Dear Xavier and Blaha,
>
>
> thanks for your reply. Yes, a dense quantity of bands is also seen in the primitive structure of Fe2VAl which has around 16 atoms. As Peter Blaha suggested, back folding of bands is only the reason due to large unit cell in the primitive case.
>
>
> Now, i want to remove this back folding of bands. Because it creates confuse when comparing the band structures while doping. Is it possible to remove the back folding by modifying the k-path or by any other means...? If yes, can you please help to do that...
>
>
> Please, have a look into this article "PHYSICAL REVIEW B 78, 165117  (2008 )". Here, i am providing a good example where the authors of this article have worked on the same structure with doping of Nb in place of V-atom and compare all band structures with doping effect. Although, they made 2x2x2 super cell from the space group (225), the bands are looks in indirect way at gamma and X point which is opposite to my observation. Does you have any idea, what they might did to avoid the band folding effects.
>
>
> Looking forward to your valuable suggestions...
>
>
> regards,
>
> Ch. venkatesh
>
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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