Questions tagged [exchange-correlation]
Questions concerning exchange-correlation terms in materials modeling calculations.
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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 ...
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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 &...
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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.
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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 :
...
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2
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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 ...
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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 ...
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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 ...
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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 ...
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Why Kohn-Sham equations are regarded as single-particle equations?
The Kohn-Sham equations are given by:
$$
\left(-\frac{\hbar^2}{2m} \nabla_{i}^{2}+V_{s}\left(\hat{\boldsymbol{r}}_{i}\right)+V_{H}\left(\hat{\boldsymbol{r}}_{i}\right)+V_{X C}\left(\hat{\boldsymbol{r}}...
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What is the physical meaning of the term "non-local interaction"?
This term pops up through out Hartree-Fock and DFT. Does this term have any physical significance to actual(real) system or it is a mathematical by-product?
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Do there exist a theoretically exact DFT method and XC functional, possibly modified from those for closed-shell molecules, for open-shell molecules? [closed]
I'm trying to analyse an extremely complex molecule's electron affinity; the molecule is much too large to perform post-HF methods on, meaning that open-shell DFT is the only option available. While I ...
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How can the GGA functionals in libxc be evaluated?
For pedagogical reasons, I started adding libxc to the atomic DFT dftatom. In this program only spherical symmetric charges. That means that the final potential is just radial.
To my understanding, if ...
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Evaluating Coulomb and exchange integrals in practice using cartesian coordinates [closed]
Many software packages provide means to calculate the Coulomb and exchange integrals, for example, the exchange
$$\int \phi^*(1) \, \psi^*(2) \frac{1}{|\mathbf{r_1} - \mathbf{r_2}|} \, \psi(1) \, \phi(...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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'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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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 ...
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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 ...
- 14.8k
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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_{...
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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 ...
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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 ...
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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 ...
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