Direct and indirect band gap

[abhishek77492652]

Hello sir,
 i am calculating the band gap of a material using atk 2017 version , but there is showing two types of band gap direct and indirect  which are unequal ? What is the meaning of showing two types of band gap ? ( photo is attached i)

[Jess Wellendorff]

This is basic solid state physics. The direct band gap is a transition for the momentum (k) does not change (horizontal transition in the band structure plot), while the indirect transition may occur between electron states with different momentum. By definition, if the fundamental (smallest) band gap is direct, the indirect gap is also the direct one. https://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps