Questions tagged [exchange-correlation]

Questions concerning exchange-correlation terms in materials modeling calculations.

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10
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2answers
184 views

Non-Convergence of the XC functional in the sense of a Taylor series

When it comes to improving the accuracy of DFT calculations, there is a well known hierarchy: starting from LDA using $E_{xc}[n]$, proceeding with GGA and its $E_{xc}[ n, \nabla n]$ dependency and ...
7
votes
0answers
48 views

How can I calculate the exchange energy for a molecule in PySCF?

I am trying to generate exchange energy separately in pyscf but didn't see a way to do that. For correlation energy, it's fairly simple but do you have any idea how to calculate exchange energy?
9
votes
1answer
89 views

Why does the PBE XC functional not appear to be a sum of exchange and correlation energy?

In the famous 1996 paper of Burke, Perdew and Ernzerhof in the very first paragraph it is stated that $E_{XC} = E_X + E_C$. Then, a GGA functional is derived starting from the energy density of ...
10
votes
1answer
129 views

DFT xc integration grid for periodic boundary conditions

I am writing my own DFT code using Gaussian basis and now I am writing the periodic boundary conditions (PBC). What integration grid people usually use for Gaussian basis PBC (+ reference please)? For ...
7
votes
1answer
258 views

How to set different exchange correlational functionals in VASP?

I want to test different exchange correlational functional on Magnesium silicide to investigate the electronic properties. For example, if I have the POTCAR library ...
9
votes
1answer
135 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-...
7
votes
1answer
96 views

What correlation effects are included in KS-DFT with LDA and GGA?

This post is inspired by this post: What correlation effects are included in DFT? The Kohn-Sham density functional theory (KS-DFT) are considered to be exact and can include all correlation effects in ...
12
votes
1answer
151 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 ...
9
votes
1answer
305 views

How does libxc calculate the potential of GGA functionals?

If the GGA xc energy is defined as $$ E_{xc}[n] = \int n(\mathbf{r}) \varepsilon_{xc}[n(\mathbf{r}), \nabla n(\mathbf{r})]\ d\mathbf{r}, $$ the potential can be written as $$ V_{xc}[n] = \varepsilon_{...
3
votes
1answer
201 views

The projector augmented wave (PAW) method, pseudopotentials (PP), and exchange correlation functionals

Disclaimer: Assume the questioner is a novice in DFT Is PAW an improvement over the pseudopotential method? In terms of Perdew, Burke, and Ernzerhof (PBE) parameterization, what is the difference ...
8
votes
1answer
87 views

Parameterization in the generalised gradient approximation (GGA)

Disclaimer: Assume the person asking is a novice in DFT and condensed matter physics in general. In the localized density approximation (LDA), the exchange correlation potential is considered a ...
29
votes
2answers
773 views

Is there any DFT code or software that has the option to use this exact exchange-correlation energy functional?

Most of the conventional DFT codes or software use LDA, GGA, meta-GGA, PBE, etc. exchange-correlation functionals, but I'm wondering if there is any DFT code or software that uses the new generation ...