[Pw_forum] The coordinate of X-point in GaAs band structure calculation

[stefano de gironcoli]

Dear Evan,

On 31/10/2016 08:51, evan wrote:
>
> Dear Stefano
>
> Thank you for your reply, but I do not understand what’s you meaning 
> in the last letter.
>
> What I want to know is that when the lattice structure of GaAs (fcc) 
> is different from the simulation cell (sc, ibrav =1 in my 
> calculations), the coordinates of high symmetry points in Brillioun 
> zone of which lattice structure (fcc or those of sc) I should specify 
> in the PWscf input file?
>
> I am not familiar with this issue, but it is important for my study. 
> Thank you for your patience.
>

then I would suggest that you get familiar with the concepts of real and 
reciprocal space, supercells and refolding of points in the Brillouin zone.
In your calculation 16 valence bands are computed. Did you wonder why 
and what they are ?
The coordinates of the X point are not your problem.

regards,

stefano
---
On two occasions I have been asked [by members of Parliament!], "Pray, Mr.
Babbage, if you put into the machine wrong figures, will the right answers
come out?"  I am not able rightly to apprehend the kind of confusion of
ideas that could provoke such a question.
                 -- Charles Babbage


> Regards
>
> Evan
>
> USC, China
>
>
>
>
>
> At 2016-10-31 14:32:53, "Stefano de Gironcoli" <degironc at sissa.it> wrote:
>
>     The one you are using: ibrav=1.
>     Do not expect to see a band structure similar to the usual one tho
>
>     stefano
>     (sent from my phone)
>
>     On 31 Oct 2016, at 03:03, evan <ewan26 at 126.com
>     <mailto:ewan26 at 126.com>> wrote:
>
>>     Dear Stefano and Andrew
>>
>>     Thank you for your kind replies. Let me ask a more general
>>     question which I think about.
>>
>>     I want to calculate the band structure of GaAs (FCC structure) in
>>     a simple cubic lattice cell with eight atoms (ibrav =1). If I
>>     specify the k points in units of 2pi/a (K_POINTS tpiba_b), the
>>     high symmetry points in Brillioun zone of which cell I should
>>     specify in the input file, FCC (ibrav =2) or those of SC
>>     (ibrav=1) lattice structure?
>>
>>     If I specify the k points in in crystal coordinates (K_POINTS
>>     crystal_b), then of which cell I should specify the k points in
>>     the input files, FCC or SC lattice structure.
>>
>>     Thank you in advance.
>>
>>     Regards
>>
>>     Evan
>>
>>     USC, China
>>
>>
>>     At 2016-10-30 02:17:33, "stefano de gironcoli" <degironc at sissa.it
>>     <mailto:degironc at sissa.it>> wrote:
>>
>>         Dear Evan,
>>            GaAS structure is zincblend (2 atoms per cell). its X
>>         point is indeed 2pi/a(1,0,0).
>>            if you choose to compute GaAs in a SC cell (8 atoms pr
>>         cell) then that point is indeed equivalent to Gamma. The zone
>>         boundary of the SC cell is pi/a(1,0,0) but this of course
>>         does not correspond to the X point of the zincblend structure.
>>           HTH
>>          stefano
>>
>>         On 29/10/2016 16:00, evan wrote:
>>>
>>>         Hello, everyone
>>>
>>>         I calculated the band structure of GaAs in a simple cubic
>>>         lattice cell (ibrav=1), I searched from the internet the
>>>         coordinates of X-point in the first Brillouin zone are
>>>         2pi/a(0,0,1) or 2pi/a(1,0,0), but both results show that
>>>         band gap occurs at G and X points simultaneously, it seems
>>>         to me that the X is equivalent to G, can you tell me the
>>>         correct X point coordinates which give me the reasonable
>>>         result. The input files and results are attached, you can
>>>         show what is wrong in the input file.
>>>
>>>         Your suggestions are appreciated.
>>>
>>>         Yours sincerely
>>>
>>>         Evan
>>>
>>>         USC, China
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>
>>
>>
>>
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>
>
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