[Pw_forum] band gap calculation

[Giuseppe Mattioli]

Dear Isaac
Why are you trying to extract the band gap value from the DOS? your DOS is just a plot calculated by applying some broadening (Gaussian, ...) to the 
eigenvalues. So look into the output of your calculation and find the highest occupied eigenvalue and the lowest unoccupied eigenvalue. The calculated 
band gap is represented by their difference. If LaFeO3 is a direct gap semiconductor both the values should be found at Gamma. Otherwise you should 
first know where is the conduction band minimum (CBM) in the first Brillouin zone, or you should use a thick mesh of k-points to be sure to include the 
CBM or a very close point. 
N.B. Use verbosity="high" if you have more than 100 k-points in your calculation and you do not see the eigenvalues printed in the output. If you use 
fixed occupations and nbnd>number of occupied states, then the code prints the highest occupied and lowest unoccupied states in the output.
HTH
Giuseppe

On Monday, January 19, 2015 05:05:15 PM Boateng Isaac Wiafe wrote:
> Dear All,
> I am trying to calculate the band gap from a density of states (DOS) plot for LaFeO3 but haven't been successful.
> 
> Upon reading around I find out that the band gap is the energy difference between the Conduction band minimum and the Valence band maximum.
> 
> >From the DOS plot below, is it right for  me to use a metre rule (*though sounds funny*) to measure the difference between the peaks/ bands at the
> >fermi level (E-Ef)?
> Please direct me if there is a better way of calculating it.
> Thanks
> 
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> ..
> Isaac Wiafe Boateng |Graduate Student
> Department of Chemistry, Theoretical and Computational Chem. Lab
> KNUST, Kumasi - Ghana
> +233 (0) 275 632712
> Alt. e-mail: boatengisaacwiafe at gmail.com

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