Bandgap Data in Materials Project

I am intrigued by the Materials Project and all the available dataset. I did a little bit of search with Semiconductor materials system that I am more familiar with. Can anyone explain the mis-match of calculated bandgap to optically measured bandgap? All the calculated GaN bandgap is around 1.4ev, while well accepted GaN bandgap is ~3.4eV.


Unfortunately, GGA-level DFT, as that employed by the standard Materials Project workflow, often severely underestimates band gaps, as in the case of GaN. There’s some additional information here.

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