The accuracy of DFT-based methods rely on the quality of the underlying functional.
To test the quality of a functional, both the band gap and the generalized Koopmans theorem
can be employed.
As the fullfillment of the Koopmans theorem garantees correct localization, we can identify
traped holes in (small) polaron states and assign the corresponding vertical transition
levels as well as the atoms where these states are localized upon.
We present a theoretical study of intrinsic defects in beta-Ga2O3, using an optimized,
Koopmans-complient, hybrid functional as an example.
It is shown that all observed photoluminescence bands of beta-Ga2O3 can be explained
by electron recombination at trapped holes, with different intrinsic defects or nitrogen
acting as hole traps.
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