[QE-users] How i can get correct band gap by GGA+U method ?

[Lorenzo Paulatto]

> I have calculated the cell parameters and band-gap energy by GGA and 
> GGA+U for CaMnO3 materiels (orthorhombic structure ). I tried two U 
> values, one from the literature (U1=4.18 eV) and I have calculated the 
> other one by the first principal method with the quantum espresso 
> package (U2=5.7722 eV ).  The band-gap energies whose I have 
> calculated by GGA, GGA+U1 and GGA+U2 are 0.71eV, 0.80 eV and 0.88 eV 
> respectively. However, these values are very small in comparison to 
> the experimental result Eg=3.07 eV.

Hello, I would proceed in two directions:

1. examine the band structure with projwfc, in order to determine which 
is the character of the states close to the gap (es. Mn d, or Oxygen 
O...). The applying a +U to those states can open the gap.

2. add an arbitrary but not absurd U to all species and see if I can 
manage to open the gap in this way or if it is absolutely impossible


cheers


>
> U2  was calculated by hp.x code in QE (version 6.5) package with 2*1*2 
> and 2*2*2 kpoints. In addition,  2*1*2 and 2*2*2 gave the same U2 value .
>
> you can find my input files below
>
> --
> *Best regards,*
> -------------------------------------
> *Mohammed Lamhani,* Ph.D.
> /LS3M Laboratory, Polydisciplinary Faculty of Khouribga, Sultan Moulay 
> Slimane University of Beni Mellal, Morocco./
>
>
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