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Questions tagged [exchange-correlation]

Questions concerning exchange-correlation terms in materials modeling calculations.

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Derivation of the Dirac exchange-energy formula

So I have been reading the textbook "Density Functional Theory of Atoms and Molecules" by Parr and Yang, and in chapter 6, their derivation of the Dirac exchange-energy functional $K_D[\rho]$...
user392401's user avatar
3 votes
2 answers
337 views

Synergy of Exchange and Correlation, Why are they Combined in the Term "Exchange-Correlation" Energy

The exchange interaction is a quantum mechanical effect that only occurs between identical particles. The effect is due to the wave function of indistinguishable particles being subject to exchange ...
Jaafar Mehrez's user avatar
7 votes
2 answers
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Self-interaction in density functional approximations for many-electron systems

In their famous paper Self-interaction correction to density-functional approximations for many-electron systems Perdew and Zunger said The exact density functional for the ground-state energy is ...
Jaafar Mehrez's user avatar
8 votes
1 answer
421 views

Where can I find BLYP pseudopotentials?

Quantum ESPRESSO doesn't support pseudopotentials for hybrid functional. Instead they suggest using pseudopotentials for the non-hybrid functional that is closer to the hybrid one, i.e., PBE for PBE0 ...
Abdul Muhaymin -Free Palestine's user avatar
7 votes
1 answer
324 views

Which strategy of improving the DFT band gap is the most effective?

DFT band gap problem is a well-known problem. LDA or GGA exchange-correlation functionals underestimate the band gap heavily. I saw some of the strategies to address this issue were: using hybrid ...
Abdul Muhaymin -Free Palestine's user avatar
7 votes
1 answer
96 views

What is just "LDA" in GPAW?

When using GPAW with the option xc='LDA', which of the potentials in https://tddft.org/programs/libxc/functionals/ is used ? Or which combination of them? Is it &...
Jellium mind's user avatar
3 votes
1 answer
87 views

Psi4 functionnals: LDA0

When comparing the energy of the LDA0 and SVWN (Slater exchange and VWN(1980) correlation), I get different results. So what is the LDA0 functional in Psi4? I can't really find literature about it.
mle's user avatar
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4 votes
2 answers
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Dirac exchange energy and X_alpha LDA methods

I want to make a DFT code (by myself) that works in the RKS LDA H2 configuration. This post is a continuation of here. Now by adding the Vosko, Wilk, Nusair correlation I have much better results : ...
mle's user avatar
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6 votes
2 answers
313 views

Is the pseudopotential designed for GGA also suited for meta-GGA?

VASP provides two sets of pseudopotentials(PP) for LDA and GGA respectively, but as I understand the PP is dependent on the exchange-correlation functional I use, so if I am using meta-GGA, could I ...
Jack's user avatar
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7 votes
1 answer
901 views

Query on using the exchange-correlation functional GGA or LDA approximation in Quantum ESPRESSO for electronic and magnetic property calculations?

I hope this question finds you well. I am reaching out to seek your advice on using the exchange-correlation functional 'GGA' or 'LDA'approximation calculation in Quantum ESSPRESSO for Calculation of ...
ismail benaicha's user avatar
5 votes
1 answer
77 views

Obtaining data for plotting Fermi and Coulomb holes of a hydrogen molecule

I need to visualize the exchange (Fermi) and correlation (Coulomb) hole of a hydrogen molecule to qualitatively illustrate the compensation of of both holes to form the total hole that is localized ...
C_Swann22's user avatar
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2 answers
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Closed-form expression for excitation energies, given the exact XC functional

In an answer to my question regarding the theoretical rigour in computing excitation energies using only the Kohn-Sham orbital energies, the rigour turned out to be nonexistent. After looking this ...
Kanghun Kim's user avatar
9 votes
2 answers
581 views

Why Kohn-Sham equations are regarded as single-particle equations?

The Kohn-Sham equations are given by: $$ \left(-\frac{\hbar^2}{2m} \nabla_{i}^{2}+V_{s}\left(\hat{\boldsymbol{r}}_{i}\right)+V_{H}\left(\hat{\boldsymbol{r}}_{i}\right)+V_{X C}\left(\hat{\boldsymbol{r}}...
Sha's user avatar
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9 votes
2 answers
801 views

What is the physical meaning of the term "non-local interaction"?

This term pops up through out Hartree-Fock and DFT. Does this term have any physical significance to actual(real) system or it is a mathematical by-product?
Alukaar's user avatar
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0 answers
98 views

Do there exist a theoretically exact DFT method and XC functional, possibly modified from those for closed-shell molecules, for open-shell molecules? [closed]

I'm trying to analyse an extremely complex molecule's electron affinity; the molecule is much too large to perform post-HF methods on, meaning that open-shell DFT is the only option available. While I ...
Kanghun Kim's user avatar
10 votes
1 answer
298 views

How can the GGA functionals in libxc be evaluated?

For pedagogical reasons, I started adding libxc to the atomic DFT dftatom. In this program only spherical symmetric charges. That means that the final potential is just radial. To my understanding, if ...
pmu2022's user avatar
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Evaluating Coulomb and exchange integrals in practice using cartesian coordinates [closed]

Many software packages provide means to calculate the Coulomb and exchange integrals, for example, the exchange $$\int \phi^*(1) \, \psi^*(2) \frac{1}{|\mathbf{r_1} - \mathbf{r_2}|} \, \psi(1) \, \phi(...
Arc's user avatar
  • 603
10 votes
2 answers
218 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 ...
A-V Labs's user avatar
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7 votes
0 answers
227 views

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

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?
Anoj Aryal's user avatar
10 votes
1 answer
213 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 ...
A-V Labs's user avatar
  • 405
10 votes
1 answer
245 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 ...
Firman's user avatar
  • 893
7 votes
1 answer
2k 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 ...
Shalini's user avatar
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10 votes
1 answer
1k 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-...
livars98's user avatar
  • 2,506
8 votes
1 answer
219 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 ...
Jack's user avatar
  • 15.2k
12 votes
1 answer
353 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 ...
Jack's user avatar
  • 15.2k
11 votes
1 answer
780 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_{...
Firman's user avatar
  • 893
5 votes
1 answer
2k 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 ...
Hitanshu Sachania's user avatar
9 votes
1 answer
156 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 ...
Hitanshu Sachania's user avatar
32 votes
2 answers
1k 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 ...
Mithridates the Great's user avatar