QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: conor.odonnell on August 23, 2018, 16:54
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Hi!
In the tutorial for using meta-GGA on thin films (https://docs.quantumwise.com/v2017/tutorials/inas_2d_mgga/inas_2d_mgga.html)
You say: "For confined systems one must first determine an appropriate value for c for the corresponding bulk system. This can be done either self-consistently or by fitting the c-parameter..."
I'm just wondering if you have a reference that justifies using the same c parameter for the thin films as in bulk?
Regards,
Conor
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Justification is based on rather general grounds. Thin film is made of a particular material. If you model that bulk material using a given DFT functional (MGGA or just GGA, or whatever). It is a plausible procedure to adopt the same DFT functional when going to thin films or dots. Otherwise, how would you compare physical quantities of the bulk and thin film systems calculated with two different functionals? That would be like comparing apples and oranges.
Of course, if you are not interested in such a comparison, you may still tune c-parameter to get the electronic structure that you think is correct, but then you have to know what is correct. Using the MGGA functional with c-parameter from the bulk calculation actually allows you to make a parameter-free prediction of the electronic structure of thin films or whatever systems comprised of that material.
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Thank you for your response! It clears up a lot for me.