29
votes
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What is band inversion and how to recognize it in band structure?
Topological materials form a broad family including insulators, semimetals, and superconductors, of which perhaps the best known are topological insulators. For concreteness, I will focus on ...
- 10.9k
22
votes
Accepted
Calculating HSE06 band structures on Quantum ESPRESSO
I have seen all the methods you mentioned but have only done one myself; I'll explain here how to use Wannier90 in conjunction with Quantum Espresso to get band structures for hybrid functional ...
- 3,081
22
votes
What are some good band-structure/DOS plotting tools/styles?
Here is an excellent answer by Andrew on pre/post processing tools available for VASP. I will introduce another tool I have used for plotting bandstructure and DOS.
PyProcar is an open-source Python ...
- 8,922
21
votes
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How to understand the time-reversal symmetry in graphene?
Two-band model for graphene. To simplify the discussion of Dirac points, it is sufficient to consider a nearest-neighbor tight-binding 2-band model for graphene. This is a spinless model because spin-...
- 10.9k
20
votes
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Are there differences in accuracy and reliability between the frozen phonon method and Density Functional Perturbation Theory?
Short answer: Modern implementations of these two methods lead to similar accuracies.
Longer answer: The calculation of phonons requires the calculation of the Hessian of the potential energy surface ...
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20
votes
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How to deduce phase transitions from a phonon calculation?
Background theory. In the harmonic approximation, the potential energy surface (PES) is expanded about an equilibrium point to second order, to obtain the Hamiltonian:
$$
\hat{H}=\sum_{p,\alpha}-\frac{...
- 10.9k
18
votes
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What are some good band-structure/DOS plotting tools/styles?
Another option is Sumo, which is a Python toolkit for plotting and analysis of ab initio solid-state calculation data. It supports VASP, CASTEP and Questaal. Plotting is mostly done through a command-...
- 701
15
votes
How to generate the high symmetry paths for band structure calculations?
If you are really interested in learning how to generate the path, I strongly advice you to avoid using any automatic tool like suggested in previous answers.
In the Wiki page entitle Brillouin zone ...
- 22.3k
14
votes
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Why is the band gap of graphene "opened" in this VASP calculation?
The reason why graphene has Dirac points at K and $-$K is because of a combination of time reversal and inversion symmetries. Therefore, if you impose these symmetries in your VASP calculation, there ...
- 10.9k
14
votes
Accepted
Si energy band values are not matching with literature values
The y-axis corresponds to the direct eigenvalues from your DFT calculation. You need to set the valence band maximum to '0' manually. The DFT output of your calculation will give the highest occupied ...
- 3,081
14
votes
Accepted
Density of States of Supercells
The density of states reads:
$$
\tag{1}
g(E)=\sum_{n}\int\frac{d\mathbf{k}}{(2\pi)^3}\delta(E-E_{n\mathbf{k}}),
$$
where $E_{n\mathbf{k}}$ are the electronic energies and the integral is over the ...
- 10.9k
14
votes
How to generate the high symmetry paths for band structure calculations?
If the crystal unit cell is in a format readable by ASE, then you can use code that looks approximately like so:
...
- 1,416
14
votes
Accepted
Easy ways to generate "teaching" band structures in Python?
I'd suggest having a look at PythTB by Sinisa Coh and David Vanderbilt, which I found very useful and easy to use.
Here's a stab at recreating the band structure of the 2d square lattice shown above
<...
- 2,524
13
votes
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mBJ-LDA band structure calculation using VASP
Here I will take Mg3Sb2 from Materials Project as an example to demonstrate the bandstructure calculation flow with the MBJ method.
(I) structure relaxation
(II) PBE band calculation based on the ...
- 14.9k
13
votes
Accepted
How to separate the data plot for spin up and spin down band structure into 2 different graphs, in Pymatgen?
Here I provide an example with my own python scripts to realize your purpose rather than using Pymatgen (You can save data firstly with Pymatgen and plot with python). I assume that you can perform ...
- 14.9k
12
votes
Rashba effect in 2D systems
Theory. The Rashba effect can be described with a 2-band model:
$$
\hat{H}=\frac{\hbar^2}{2m}(k_x^2+k_y^2)\mathbb{1}_2+\alpha_{\mathrm{R}}(\sigma_1 k_y-\sigma_2 k_x),
$$
where $\alpha_{\mathrm{R}}$ is ...
- 10.9k
12
votes
Accepted
How to make a good HSE06 bandstructure for TMDC monolayer material (e.g.: WS2) in terms of VASP calculation INPUTS?
I. self-consistent at PBE level. [1scf]
II. band calculation based on previous converged charge density. [2band]
III. HSE self-consistent calculation based on PBE self-consistent wavefunction. [...
- 14.9k
12
votes
How to know optimal K-points grid values for good DFT calculation?
Like many other parameters in QE one of the best methods is to simply test yourself and weight your options.
You may start with 1x1x1 and go to 3x3x3 for example and check the following.
Do you get ...
- 121
12
votes
Accepted
How to know optimal K-points grid values for good DFT calculation?
As already specified in the previous answers, the choice of K-Grid mesh should be taken upon verifying the convergence of the desired quantity. We usually start with the convergence of the total ...
- 3,238
12
votes
Is there an energy gap correction factor that needs to be used in DFT calculations?
I would like to add a few clarifications to Jack's answer:
Standard DFT calculations with fixed ionic positions are actually not even 0 K. A better way to describe them is that they are static ...
- 10.9k
12
votes
How to calculate the band structure of a protein molecule
Band structure is a concept for periodic system only. As proteins are not periodic structures, they don't have electronic bands.
The fact that you can download a PDB file (or a CIF file) with ...
- 22.3k
11
votes
How does the mBJ potential give an accurate band gap as compared to LDA and GGA?
Model potentials for exchange:
Exchange-correlation potentials like mBJ and GLLBSC have model orbital-dependent corrections included in the form of the functional. I'll first try to get the ...
- 1,416
11
votes
Accepted
conceptual problem about the energy band along the High symmetry point in the Brillouin zone
I will try to outline this in simple terms. There are certainly more rigorous explanations.
The high-symmetry points in the Brillouin zone are those that remain physically identical when certain ...
- 876
11
votes
Accepted
How to start with structural defects in monolayer?
First of all, I assume that you are taking VASP to perform your calculation.
Secondly, I assume that your structural defect is taking a Hf atom from your structure. (You can deal with substitutional ...
- 14.9k
11
votes
Is there an energy gap correction factor that needs to be used in DFT calculations?
Is this calculated indirect bandgap at room temp. or at 0K?
QE is based on the density functional theory (DFT). DFT is a ground-state (0K) theory and hence the calculated bandstructure is 0K.
If it ...
- 14.9k
11
votes
How to model an anti-ferromagnetic crystal in quantum ESPRESSO properly?
The key point is the setting of starting_magnetization. You can find an explanation on the pw.x input description page.
Here I give you an example to set this tag. The structure picked here is the ...
- 14.9k
11
votes
How to create a 3D band structure from DFT band structure calculation?
Consider a graphene Hamiltonian, whose dispersion looks a lot like the one in your figure. Per these notes, its k-space Hamiltonian may be written as:
$$
H(k)=-t \sum_{\delta} [\cos(k\cdot\delta)\...
- 2,281
11
votes
Accepted
How is the right k-path chosen for band structure?
There is no such thing as "correct path". The only condition you should use to select the path is that it has to be continuous, only that. After that, the selection will depend on what are ...
- 22.3k
11
votes
Accepted
Fermi Energy in Band Structure
In electronic structure calculations of finite systems, there is a well-defined energy scale: 0 is the vacuum energy, and any electron with positive energy is unbound.
For materials, the story is ...
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