25 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 ...
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20 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 ...
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18 votes
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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 ...
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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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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-...
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17 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{...
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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-...
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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 ...
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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 ...
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13 votes

How to deduce phase transitions from a phonon calculation?

The answer of @ProfM is already very complete, but I wanted to tackle your question from a more practical point of view. The presence of imaginary frequencies indicate that there are atomic positions ...
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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 ...
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13 votes
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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 ...
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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10 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)\...
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10 votes
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Does the spin polarised DFT calculation mean broken time reversal symmetry?

Yes, broken symmetry solutions do break time-reversal symmetry, and that's one of the reasons why they are unphysical when the total magnetic moment of the system is 0 (although they are physical when ...
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10 votes

Why the band structure of a slab is not smooth?

1. Is it possible that the energy gap of the material is direct in the bulk but indirect in the slab? Yes, this is possible (as is the reverse). The 2D slab does not have the same symmetry as the full ...
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Properties that can be deduced from Band structure and DOS

Some of the properties we can get from the band structure are: Band gap: energy between the bottom of the conduction band (CB) and the top of the valence band (VB). The gap will give you if the ...
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Physical origin for higher bandgaps when going from bulk to few-layers

Quantum confinement can occur when the exciton (electron-hole quasiparticle) radius is larger than the size of the semiconductor. Due to this confinement, the energy levels which can be occupied by ...
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