What do you mean by slightly upper? Isn't it a conductor/metal?

For sure you don’t provide many piece of information here… So your plot suggests that your system is metallic. Which system is this? Is this a bulk or layered material?

Do you expect your system to be a semiconductor/insulator instead? Why? Is there numerical evidence for that (not experimental since that might be difficult to reproduce)?

If that is your expectation, how well are the parameters of your calculation converged? Which method did you use? You have an extremely flat band between R and M — this is what you expect?

Again, before asking why something does not work, think on how we can help if you do not provide enough pieces of information..

Dear Roberto D'Agosta,

I was calculating band gap in materials studio 2020 (Castep)

I was expecting this would be a semiconductor cause I've put enough pressure on it.But I think you're opinion is highly logical that it is a metal that's why showing this.But extremely flat band between R & M. What is the probable reason for that that? will you please help me with any kind of info?

Thanks.

First of all zoom in plotting only the bands around the gap. The see how big is the intersection between the Fermi energy and the valence band.

are you sure your calculation parameters are well converged? There is no residual forces between atoms?

cheers,

roberto