Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Density Functional Theory (DFT) is not appropriate in predicting the band gap of the materials. However, which functional gives close value to the experimentally observed band gap of semiconductors? Any one of the following functional can give a close prediction of band gap?

LDA - PWC, VWN

GGA - PW91, BP, PBE, BLYP, BOP, VWN-BP, RPBE, HCTH.

What about the HOMO-LUMO gap? Can we use HOMO-LUMO gap (for non-periodic structures) instead of the gap observed in density of states?

share|improve this question
1  
Part of what makes this site enjoyable for everyone, is that even if one is not able to answer, many times one can still understand the question. This question uses a lot of technical jargon and abbreviations. It would be good if OP (or somebody else?) could make this question more broadly readable. –  Qmechanic Apr 18 '13 at 19:16

1 Answer 1

which functional gives close value to the experimentally observed band gap of semiconductors

Different functionals are accurate under different circumstances, so you can't make a blanket statement that one functional gives accurate band gaps for semiconductors. The only way to know when various functionals are and are not trustworthy is to use them in order to become familiar with their strengths and limitations. Personally I suggest to choose a small number of well known functionals (I use PBE and B3LYP) and stick to those unless you know why some other functional is more appropriate for a given situation.

What about the HOMO-LUMO gap? Can we use HOMO-LUMO gap (for non-periodic structures) instead of the gap observed in density of states?

The band gap in periodic systems is the continuous version of the HOMO-LUMO gap for molecular systems, so there's no using one instead of the other. If you're asking whether the HOMO-LUMO gap of an isolated molecule is similar to the band gap for an atomic or molecular crystal, the answer is no, they're often totally different.

share|improve this answer
1  
+1 couldn't have said it better! –  Rafael Reiter Apr 18 '13 at 15:43
    
@phyphenomenon Also, as you say, DFT is notorious for systematically underestimating band gaps, so if you want high precision numbers for band gaps then you'll anyway need to move to a better approximation such as the GW method. –  Douglas B. Staple Apr 18 '13 at 15:43
    
The answer by Douglas B. Staple is useful. I have another question regarding this. Some researchers use Hydrogen atom termination, to model a non periodic finite sized 2D structure as a periodic one. Since this is a non periodic system, HOMO-LUMO gap only can be calculated. Here also the band gap is not similar to the periodic model? –  phyphenomenon Apr 19 '13 at 4:15

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.