Questions tagged [kohn-sham]

Questions related to the Kohn-Sham approach to DFT.

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16 votes
1 answer
930 views

Difference between Van der Waals (DFT-D and DFT-D3) corrections in ab-initio calculations

In Kohn-Sham DFT calculations, Van der Waals corrections are often implemented in the structure optimization calculations because the typical functionals such as LDA and GGA are found to not treat ...
  • 2,336
9 votes
1 answer
58 views

Extended Hybrid Methods

Hybrid DFT methods, where the functional is supplemented with Hartree-Fock exchange, have become increasingly popular due to their low cost and decent accuracy. Double hybrids, which mix in an MP2 ...
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5 votes
1 answer
100 views

Question on generalised Kohn-Sham "band gap"

It is often said that the optical band gap, i.e. the first excitation energy, of a species is exactly equal to the difference between the (Kohn-Sham) HOMO and LUMO. This would mean that the state of ...
25 votes
3 answers
1k views

Given that Kohn-Sham DFT is strictly a ground-state method (at 0 K), how is it sufficient to describe materials in real-life applications?

Kohn-Sham DFT appears to be so popular even though it is strictly a ground-state method - all calculations are done at 0 K. How then, is it so popular when describing materials that have real-life ...
  • 2,336
16 votes
4 answers
239 views

Do eigenvalues in DFT mean anything?

My question is specifically related to the molecular energies of Kohn-Sham DFT: Do eigenvalues in KS-DFT mean anything?
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12 votes
1 answer
195 views

What's the physics contained in the exchange-correlation functional in the framework of KS-DFT?

This question is inspired by this post. In the Kohn-Sham framework of density functional theory, the total energy is expressed as: $$E=E_{kin}^{non}+E_{ext}+E_{H}+E_{xc}$$ in which The first term is ...
  • 14k
18 votes
2 answers
181 views

Is there any relevant DFT formalism apart from the Kohn-Sham approach?

I wonder if all DFT codes are based on the Kohn-Sham formalism?. If other methods are available, what are their scopes?
  • 8,432
16 votes
2 answers
350 views

Is the electronic band gap the only thing that is affected, when switching from standard KS-DFT to Hybrid functionals?

It is very well known that Kohn-Sham DFT underestimates bandgap. To get an accurate estimate of the bandgap, people often turn to Hybrid functionals (if they don't want to perform the actual ...
  • 2,336
12 votes
2 answers
142 views

Procedure to classify errors in Kohn-Sham DFT

I was reading this paper which basically outlines the two main types of errors that one encounters in Kohn-Sham DFT : Density-based errors and Functional-based errors. I understand the practical ...
  • 2,336
12 votes
3 answers
153 views

Physically motivated double hybrid DFT?

This question came to mind while writing another question here Extended Hybrid Methods, but I felt it was distinct enough to ask separately. In double hybrids DFT methods, you essentially perform a ...
  • 14.3k
12 votes
2 answers
549 views

How can we say that the KS equation is describing a noninteracting many-electron system?

Based on HK's two theorems, the density functional theory was built. Because one can't find the universal energy functional $F_{HK}[n(r)]$, Kohn and Sham further proposed the Kohn-Sham ansatz: mapping ...
  • 14k
9 votes
1 answer
313 views

'Exchange' in Hartree-Fock and Kohn-Sham DFT

I am a bit confused about the notions of exchange in the Hartree-Fock and Kohn-Sham Density Functional Theory schemes. In Hartree-Fock, one just writes down the many-electron wavefunction as a hartree-...
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5 votes
2 answers
225 views

Relationship between functional derivative and potential value at a position

Thanks to very helpful and detailed answers for my previous question, I understand the functional derivative of the energy with respect to the density. In addition, this functional derivative is equal ...
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