BAND gap of Cu2O Bulk

[Om Prakash Upadhyay]

Hello.....
            I am calculating the band gap of Cu2O bulk structure of (2*2*2) taking k-point sampling of k=3*3*3 using ATK_DFT, exchange correlation SGGA_RPBE, LCAO: Cu-DZDP O-DZP, mesh cut off=75 hartree.
The experimental band gap value of Cu2O is about 2.17 eV with direct band gap. But in my calculation I found about 0.2 eV only with direct band gap.
Why this is happening? Are my calculation parameters wrong in my calculation? What should i have to do to get better value of band gap?
                                             Reply plez........................

[zh]

It is well known the GGA or LDA seriously underestimate the band gap. Your results  are normal.

[Om Prakash Upadhyay]

Is this band gap well for further calculation  for its nanowire?

[Ulrik G. Vej-Hansen]

That depends on what you want to do. If you need an accurate band gap, you can use MGGA instead of regular GGA, but if you plan on doing adsorption, as suggested by your sue of RPBE, then it might not be so important that you have the right gap, as long as there is a gap. But it depends on exactly what you want to do.

[Daniele Stradi]

There was already a lengthy discussion on this in the Forum. Check:
http://quantumwise.com/forum/index.php?topic=4111.msg18783#msg18783