[Wien] The PBE- and EV-GGA show the different maximum in the highest valence band

[Joey Davis]

Dear all,
                     
I use PBE-GGA and EV-GGA to calculated the band structure of a narrow gap semiconductor.
 The semiconductor in my calculation is a bulk compound, and there is no reports about its band
 gap information. It is well known that EV-GGA can give the band gap value that is close to the
 right value. Usually I use PBE-GGA to calculated the energy band structure, and shift the
 conductive band to force the band gap to be the value given by the EV-GGA. But in my
 calculation, the PBE-GGA shows my semiconductor is a indirect band gap semiconductor, and
 the EV-GGA shows that it is a direct band gap semiconductor.  In an other words, the PBE-GGA
and the EV-GGA show the different maximum in the highest valence band. I want to get the correct 
value of band gap in my semiconductor, and what should I do? The spin orbit coupling is included in
 my calculation.  Thanks in advance

Best wishes
 Joey Davis 
 
       
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