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Questions tagged [functional]

For questions about the design and use of specific exchange-correlation density functionals

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Examples of low sensitivity of observable behavior to the choice of DFT functional

This question is the antipode to another one I just asked. Here I am looking for examples where not immediately obvious properties are predicted well by a range of functionals or pairs of rather ...
Andrey Poletayev's user avatar
6 votes
0 answers
57 views

Examples of high sensitivity of observable behavior to the choice of DFT functional

Most computational materials science studies perform or reference some sort of baseline process for choosing the DFT functional that they will employ to model their system. It is unlikely that a ...
Andrey Poletayev's user avatar
8 votes
2 answers
119 views

What is the Hamiltonian in the adiabatic connection?

I am trying to understand the adiabatic connection as motivation for hybrid functionals that include Hartree-Fock like exchange. While it sounds intuitive that the exchange of the noninteracting Kohn-...
Hans Wurst's user avatar
2 votes
0 answers
92 views

When calculating DOS and band structures, do I still need to provide a regular mesh for MetaGGA functionals as in the case with hybrid functionals?

In VASP manual it is mentioned that the deorbitalized versions of SCAN and R2SCAN MetaGGA functionals do not depend on the kinetic energy density but instead on the Laplacian of the charge density. ...
khaledb99's user avatar
7 votes
1 answer
298 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
6 votes
1 answer
1k views

How to calculate DOS and band structure using hybrid functional in Quantum Espresso?

After I run an SCF calculation with PBE0, I want to use calculation= 'nscf'/ (‘bands’) with PBE0, but this message occurs: ...
SOELHADFI's user avatar
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6 votes
2 answers
292 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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6 votes
1 answer
108 views

could meta-GGA-r2scan descript d electron localization and polaron the same as Hybrid functional?

I notice that r2scan could be more accurate than rscan, but I am unsure if r2scan could describe the d electron localization without Hubbard+U? Or do I still need Hubbard+U with r2scan?
Jack's user avatar
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8 votes
1 answer
403 views

Do I have to use the same functional for dielectric function calculations, as the one used for relaxing the structure?

This is a general question regarding the practices of doing optical calculations and the role of the ionic contribution to the dielectric function (with heavy reference to VASP). Based on VASP's ...
CW Tan's user avatar
  • 1,316
3 votes
1 answer
89 views

Decay rate of DSD-PBEPBE-D3BJ

I gave up on the wB97X-2(TQZ) functional, which would have an exact decay rate of -1/r, re: my previous question and decided to use DSD-PBEPBE-D3BJ, which is available on vanilla Psi4. I then looked ...
Kanghun Kim's user avatar
4 votes
1 answer
262 views

Is the mBJ functional reliable for band structure calculations in VASP?

I am currently looking at band structure mainly for a few magnetic compounds. Due to having a large super-cell my calculations have not converged with the HSE06 functional. So I looked at what else is ...
Chan's user avatar
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3 votes
0 answers
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Tips for using Hybrid Functionals in VASP [closed]

I am planning to use HSEO6 to calculate the band structure and DOS of a perovskite super cell. My cell has about 80 atoms. Furthermore I have also used dispersion correction and I will also have to ...
Parmeet Singh EP 066's user avatar
6 votes
1 answer
257 views

For what DFT functional is useless to add D3 or similar corrections?

I would like to know for which DF is useless to add dispersion corrections. For example, I suppose that for the nonlocal density-based functionals such as wB97M-V it is unnecessary because the ...
NickZ's user avatar
  • 1,499
11 votes
2 answers
498 views

DFT functionals from MP2 methods

I have heard people talk about DFT functionals built starting from MP2 corrections. Do you happen to have a reference I read about that from?
Yepman's user avatar
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10 votes
3 answers
577 views

Which DFT functional should I use to simulate spectra of pesticides?

I am mainly searching for functionals to calculate spectra of pesticides. I found the benchmark test from Goerigk and Grimme$^1$, but don't understand which of the functionals suits my purpose the ...
Till's user avatar
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26 votes
3 answers
4k views

What does B3LYP do well? What does it do badly?

I have seen a general criticism of B3LYP in computational chemistry (especially with the 6-31G* basis set). I would like to know some of the more/less obvious problems that occur when using it and ...
Tristan Maxson's user avatar
8 votes
1 answer
985 views

Regarding spin-orbit coupling on DFT codes

In most DFT codes like QE and VASP, spin-orbit coupling (SOC) can be incorporated by employing fully relativistic pseudopotentials. My question is with regard to the implementation of SOC among ...
livars98's user avatar
  • 2,496
12 votes
2 answers
202 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 ...
livars98's user avatar
  • 2,496
12 votes
3 answers
1k views

Total energy from KS-DFT: How reliable is it and why?

As the title suggests, my question is fundamental - How reliable are the total energy values from Kohn-Sham Density Functional Theory, and why. I acknowledge that absolute values of energies are ...
livars98's user avatar
  • 2,496
8 votes
1 answer
327 views

HSE06 Starting Guess

In CASTEP, can you start with a converged density for a lower level of theory for a starting guess for HSE06? If you can, what functional is suggested or is it something that will cause more headache ...
Tristan Maxson's user avatar
10 votes
2 answers
815 views

Is there a list of all functionals?

A quick google search of the Minnesota Functionals will lead you to the wikipedia page on them where it will state the following: ...
Cavenfish's user avatar
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19 votes
1 answer
551 views

Promising functionals for transition metal chemistry

I'm looking to get your opinions on the most promising density functionals to use for thermochemistry and kinetics of transition metal complexes. However, as eloquently laid out by Tom Manz on this ...
Andrew Rosen's user avatar
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12 votes
2 answers
1k views

Are meta-GGA functionals SCAN (and its variants) ok to use in planewave DFT with the PBE pseudopotentials?

The meta-GGA SCAN functional has been there for a while. Despite the lack of SCAN (ultrasoft/PAW) pseudopotentials, various works used it in plane-wave pseudopotential calculations with ...
bzbzbz's user avatar
  • 721
14 votes
1 answer
210 views

Why are single excitations ignored in the MP2 component of double hybrid functional calculations?

In the original paper by Grimme introducing double hybrid functionals (also summarized in just 3 paragraphs here), it says: "[As] opposed to nonempirical versions of KS-PT2 [19], the single ...
Nike Dattani - No Free Time's user avatar
16 votes
4 answers
469 views

What is the role of a chemist in computational chemistry?

As someone that wants to learn about computational chemistry, mainly for its use in energy storage materials (and therefore DFT as the most practical method of it), I am wondering what is essential ...
Georgios Karaiskakis's user avatar
25 votes
4 answers
1k views

Mathematical expression of SCAN (Strongly Constrained and Appropriately Normed) constraints in DFT

(This question is originally posted on physics stackexchange, but someone suggested me to post on this site, so there you go) I'm compiling the mathematical expression of SCAN (Strongly Constrained ...
Firman's user avatar
  • 893
16 votes
2 answers
679 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 ...
livars98's user avatar
  • 2,496
14 votes
1 answer
1k views

Is LDA better than GGA for elastic constants?

I have calculated elastic constants for Si, GaAs, and GaN using LDA and GGA in VASP. LDA is giving better results than GGA for elastic constants. Is there is a reason behind the good results by ...
sonia rani's user avatar
12 votes
1 answer
154 views

Justification for use of Screened Functionals

Hybrid density functionals with screened Hartree-Fock exchange at long range have become popular for modeling solids. I'm curious as to what the reasoning is behind this functional form. I understand ...
Tyberius's user avatar
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15 votes
1 answer
337 views

What are good basis sets and functionals for Ni, Cd and Pb?

I will setup a single point energy calculation using Gaussian for a system containing atoms of B-N-Ni, B-N-Pb and B-N-Cd. The system are slabs of boron-nitride [1,2] interacting with those metals. ...
Camps's user avatar
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44 votes
16 answers
3k views

What are some recent developments in density functional theory?

In the book Materials Modelling Using Density Functional Theory: Properties and Predictions by Feliciano Giustino, a timeline of milestones in DFT was given for achievements between 1964 and 1996: $$\...
Thomas's user avatar
  • 9,132
18 votes
1 answer
1k views

Are there problems with the Tran-Blaha modified Becke-Johnson potential (mBJ, a.k.a. TB09) in Quantum ESPRESSO?

I have used the modified Becke-Johnson (mBJ) exchange potential before, as it was developed and implemented in Wien2K by Fabien Tran and Peter Blaha (1). In 2013, Éric Germaneau et al. implemented mBJ ...
epalos's user avatar
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15 votes
1 answer
123 views

Functionals/basis sets optimized with respect to properties?

In general (at least for molecular calculations) basis sets and DFT functionals are fit to some high level calculation or experimental energy. It is speculated that an accurate energy will result in ...
Tyberius's user avatar
  • 15.5k
27 votes
2 answers
1k views

What are the best functionals for transition metal compounds?

Some properties of transition metal compounds can be influenced by static correlation, relativistic effects, and, in some cases, close-lying electronic states could result in difficulties in SCF ...
Verktaj's user avatar
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54 votes
5 answers
2k views

What is the closest thing we have to "the" universal density functional?

It is understood that finding "the" universal functional is an NP-complete problem. However, progressively better functionals have been constructed decade after decade and fitted to more and more ...
Nike Dattani - No Free Time's user avatar