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8 votes
Accepted

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

It's a nice question, it will be difficult to compare their accuracy and efficiency in a single plot, because the band gap problem is mainly divided into two parts: the self-interaction and the ...
M06-2x's user avatar
  • 916
8 votes
Accepted

Materials with low band gap and low conductivity simultaneously. Is it possible?

There are such materials! See chp. 11 in Girvin-Yang which gives a much better discussion than I am providing here. You could probably also look up 'Anderson insulator' online or in any other solid-...
Tyler Sterling's user avatar
8 votes

How to find the band gap energy value in Quantum ESPRESSO?

If you are treating your material as a non-metal (i.e. not using any smearing and using occupations='fixed'), then you can get ...
Abdul Muhaymin -Free Palestine's user avatar
7 votes
Accepted

What parameters should be checked on both unit cell and super cell to make sure the calculations are going fine?

Here are some thoughts about calculations involving primitive cells and supercells: The energy cutoff used should be the same between a primitive cell and a supercell. The density of $\mathbf{k}$-...
ProfM's user avatar
  • 11.1k
6 votes

How to choose the best U value for studying the electronic properties?

U values are in general non-transferable the U-value found in the literature will not give you the same band gap in general unless you know the exact structure, pseudopotentials, DFT code and their ...
Abdul Muhaymin -Free Palestine's user avatar
6 votes

Direct and Indirect bandgap

In order to know if your material has direct/indirect band gap, you need to calculate the electronic band structure: Energy vs k. Then, you look for the smaller $\Delta E$ between the bottom of the ...
Camps's user avatar
  • 23.4k
5 votes
Accepted

Question on generalised Kohn-Sham "band gap"

The optical band gap is not expected to equal the DFT band gap since excitonic effects are not included. What you are referring to is the fundamental gap. The fundamental gap is related to electron ...
AGS's user avatar
  • 1,141
5 votes

How do I obtain CB and VB values from Quantum ESPRESSO?

I would recommend to obtain VB top and CB bottom energy values from the output file. The occupation numbers are listed if 'verbose' mode is active. In any output mode the energies should be printed ...
Leon A's user avatar
  • 91
5 votes

How do I obtain CB and VB values from Quantum ESPRESSO?

From the graph you presented: Select the Brillouin $\Gamma$ point, $G$ in the graph (this is for a direct gap system). Look for where the Fermi level is. In the graph, it is indicated by the red ...
Camps's user avatar
  • 23.4k
5 votes

Indirect to direct band gap transition in SUPERCELLS?

This is allowed, in fact you can almost always construct a supercell where this has to happen. Consider the band eigenvalue at k-point $\vec{k}=(0,0,\frac{1}{p})$ in a given unit cell; if I now make a ...
Phil Hasnip's user avatar
  • 8,012
5 votes
Accepted

Negative band gap in DFT calculations

Some materials erroneously give a metallic state even if it isn’t. Depending on what type of material and exchange-correlation functional you use, this can be more or less likely to happen. With ...
AGS's user avatar
  • 1,141
5 votes

Extracting band structure data using Boltztrap for Quantum ESPRESSO

I don't see a way to do this from the command-line, but as BoltzTraP2 is written in Python, you can add it in. This worked for me: Edit "interface.py" and go to the "parse_plotbands&...
Phil Hasnip's user avatar
  • 8,012
4 votes

Band gap do not match to published result in DFT using BURAI GUI of Quantum Espresso

Since you used BURAI, it's safe to assume that you used either an LDA or a GGA functional for your pseudopotentials (PP). In order to confirm, check if you have pz or pbe in the name of your PP. It ...
Abdul Muhaymin -Free Palestine's user avatar
4 votes
Accepted

Determining the Nature of a Material's Band Structure: Metallic or Semi-Metallic?

(Edited after discussion with the asker and seeing the zoomed-in band structures. A commenter suggested adding Addison of hybrid functionals as a correction to the band gap underestimation of [...
elutionary's user avatar
3 votes
Accepted

Can a material be a conductor in one direction and a semiconductor in another direction?

If I understand your question, the answer is yes. Really, the only requirement is anisotropy. Consider e.g. a half-filled 1d chain. It is metallic along the chain and insulating perpendicular to it. I ...
Tyler Sterling's user avatar
3 votes

How do I obtain CB and VB values from Quantum ESPRESSO?

To obtain both the VB and CB you will have to run scf calculation by using the nbnd command (the number of Kohn-Sham states) with a value basically the same as the ...
Youssef Chlikhy's user avatar
3 votes

Optical Band gap determination from absorption coeffecient using DFT

You can calculate the optical gap with TDDFT or GW/BSE. GW/BSE is more common in solids. These are more expensive calculations than DFT calculations, but they are commonly done in metal-halide ...
AGS's user avatar
  • 1,141
2 votes

Optical Band gap determination from absorption coeffecient using DFT

This is not the actual answer that you asked, but you can get some insight from here. I believe the optical gap is equal to the direct electronic gap at T=0K at a certain k point. Still some more ...
1 vote

Problem with k-points with pw2wannier

I assume that you used open_grid.x in order to expand the k-point grid from IBZ to full BZ. In this case the k-point mesh should be taken from the output of open_grid.x. Also I found that when using ...
Leon A's user avatar
  • 91

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