[Wien] Basic question regarding band gap calculation using GGA+U approach

[tran at theochem.tuwien.ac.at]

Hi,

Not to my knowledge. In addition such thumb rule would be difficult
to apply when the band gap with LDA/GGA is zero.

F. Tran

On Tue, 11 Nov 2014, shamik chakrabarti wrote:

> 
> Dear wien2k users,
> 
>                            We know that charge transfer type band gap
> (transition metal d - oxygen p) is generally underestimated in simple DFT
> calculation. Situation may improve a bit by using DFT+U approach, however,
> more accurate band gap may be found in Hybrid-DFT calculation. 
> 
> Now, my question is that is there any scaling factor by which the
> underestimation for a charge-transfer type gap in a simple DFT calculation
> can be approximated.   
> 
> Say, in a simple DFT we have found 0.5 eV gap for charge transfer type
> states...then whether it can be said that the accurate gap may be 1.5
> eV...that mean there is an underestimation of 1 eV for a charge-transfer
> type gap in simple DFT calculation......whether there is any such thumb rule
> like that or it strictly depends on the system under consideration?  
> 
> Any response in this regard will be very helpful for us.
> 
> Thanks in advance.
> 
> with regards,
> 
> 
> --
> Shamik Chakrabarti
> Senior Research Fellow
> Dept. of Physics & Meteorology
> Material Processing & Solid State Ionics Lab
> IIT Kharagpur
> Kharagpur 721302
> INDIA
> 
>