QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Luis M. Villamagua C. on February 17, 2014, 09:45
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I was said that geometry optimization had to be carried out by DFT. Should I calculate DOS and Band Structure with tight binding? or should I continue using the same framework?
Regards,
Luis
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That's a tricky question. On the one hand you want to take e.g. surface reconstruction into account, but on the other hand the TB model may not have this kind of flexibility. Some TB models have matrix elements that are functions of the distance between atoms and can at least attempt to take this into account, like Huckel and DFTB and some nearest-neighbor models. But the equilibrium of the model is usually chosen at the experimental lattice constant, so at least one should use that for the basic crystals, and only let surfaces relax. But DFTB on the other hand has quite good relaxation capabilities, so one needs to distinguish different TB models from each other.
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For example, to calculate the electronic properties ...
(1) If I continue using DFT, should this ensures that the results I will get will be accurate?
(2) If I use TB, could I not get accurate results?
I am new with the topic, so I would appreciate if you can help me choosing the more convenient route.
Thanks again,
Luis
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There is no universal guarantee of "accuracy" in this game... :-\
DFT may get the band gap wrong for semiconductors but is (often) accurate for geometries. NNTB doesn't work for metals. Empirical models are only as good as what they were fitted too - and sometimes not even that, and sometimes surprisingly good for other things too. You will have to learn by experience and comparison what works for your problems.