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Why is density functional theory unreliable for calculation of band gap?

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    $\begingroup$ Maybe the question is supposed to start with "Why"? In any case please add some context $\endgroup$
    – Yuriy S
    Feb 4 '20 at 10:52
  • $\begingroup$ Is it? Historically, DFT has had problems, particularly with narrow gap materials. Not surprisingly, people have worked hard to improve the functionals and understand where some of the algorithm/numerical problems are and how to avoid them. But, this is kind of like asking why RK methods are better then direct forward integration to solve many differential equations. $\endgroup$
    – Jon Custer
    Feb 4 '20 at 13:36
  • $\begingroup$ This has been answered here. $\endgroup$
    – rashid
    Feb 18 '20 at 5:04