[Pw_forum] band gap from hybrid pseudopotentials

[毛飞]

在2016-08-05，saqlain <saqlain at bilkent.edu.tr> 写道:-----原始邮件-----
发件人: saqlain <saqlain at bilkent.edu.tr>
发送时间: 2016年8月5日 星期五
收件人: PWSCF Forum <pw_forum at pwscf.org>
主题: Re: [Pw_forum] band gap from hybrid pseudopotentials

Dear Evan
Thanks for your reply. However, I still have some confusions, if you can help to resolve these.
1. I have not use smearing in the calculations. What happens if smearing is used? I haven't yet understood how to get Fermi energy. The output file is attached, if you can help me figure out the value and the procedure to see this value
You can get the Fermi energy of your system when you add some smearing in the scf calculation.
2. When I use plotbands.x it asks a few questions, can you tell me what is meaning of this question {deltaE, reference E (for tics)}
I think these questions are self-explantory, deltaE is the distance of the adjant two points in the band structure, for reference E, you can put the maximum of the valence band, then the maximum valence band is shifted to 0 eV in the plot. you can follow some tutorials:http://www.fisica.uniud.it/~giannozz/QE-Tutorial/
 
3. What are these values? and where would these are to be used?

high-symmetry point:  0.0000 0.0000 0.0000   x coordinate   0.0000
high-symmetry point: -0.0016 0.0000 0.0856   x coordinate   0.0857
high-symmetry point: -0.0016 0.0861 0.0856   x coordinate   0.1718
high-symmetry point:  0.0841 0.0861 0.0840   x coordinate   0.2575
high-symmetry point:  0.0857 0.0861-0.0016   x coordinate   0.3432
high-symmetry point:  0.0000 0.0861 0.0000   x coordinate   0.4289
high-symmetry point:  0.0857 0.0000-0.0016   x coordinate   0.5504
high-symmetry point:  0.0841 0.0000 0.0840   x coordinate   0.6361

4. In your message you wrote, band gap = I-A, what is I and A????
I: Ionization energy; A: Affinity energy

I am an experimental guy, and have recently joined dft calculations, so have a little idea about these things. extremely sorry for this.
Cheers
Msaqlain


On 08/05/2016 06:14 AM, 毛飞 wrote:

Hello, Msaqlain
> -----原始邮件-----
> 发件人: saqlain <saqlain at bilkent.edu.tr>
> 发送时间: 2016年8月5日 星期五
> 收件人: pw_forum at pwscf.org
> 抄送: 
> 主题: [Pw_forum] band gap from hybrid pseudopotentials
> 
> Dear QE users
> 
> I would like to use QE for calculating band gap with hybrid 
> pseusopotentials approach.
> 
> after going from the discussions available at different sites, I have 
> done the calculation in this way: vc-relax the system, did scf and then 
> nscf followed by band structure calculation. My questions are,
> 
> 1. How can I now extract the band gap from the file generated by bands.x?
The output file generated by bands.x can be processed by plotbands.x to plot the band structure, then you can obtain the band gap.
 
> 2. in the scf and nscf output files, I can't see Fermi energy. How can I 
> know about the Fermi energy?
Do you add some smearing in these calculations?
 
> 3. The scf and nscf files contain, highest occupied and lowest occupied 
> levels? what is meaning of this? does the highest occupied level mean 
> Fermi energy?
No, for insulators (which shows the electronic band gap), the Fermi energy stays between the HOMO and LUMO
 
> 4. does the difference of highest occupied and lowest occupied level 
> correspond to band gap?
No, the band gap Eg = I-A.
 
regards
evan
> your response would be highly appreciated
> 
> Msaqlain
> 
> Bilknet, Ankara. Turkey
> 
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> Pw_forum mailing list
> Pw_forum at pwscf.org
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