14
votes
Running Quantum ESPRESSO calculations in Google Colab
A little background on why I asked this question:
I have a desktop PC with an AMD Ryzen 5 processor, 4 cores 8 logical threads and 32GB DDR4 RAM. I'm trying to do DFT-GGA calculations on a 2D Xene ...
- 1,091
13
votes
Accepted
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 ...
- 14k
13
votes
Doubt about energy convergence with different k points
Let's just remind ourselves what k point sampling is. It is used to approximate the integral of a function over the Brillouin zone by replacing the integral with a sum over a finite number of points:
$...
- 634
12
votes
Accepted
Increasing supercell size to increase K-points sampling
Short answer: Yes, doubling the volume of the simulation cell you will be able to effectively sample a finer $\mathbf{k}$-point grid to calculate the dielectric function. However, the calculation will ...
- 10.4k
12
votes
How to generate KPOINTS file for HSE06 band-structure calculations?
The usual strategy to perform a band structure calculation in DFT has two steps:
Perform a self-consistent calculation using a uniform $\mathbf{k}$-point grid to determine the self-consistent ...
- 10.4k
12
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:
...
- 1,346
12
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 ...
- 19.2k
12
votes
Accepted
What does occupations='tetrahedra' mean in Quantum ESPRESSO?
For the "why" you should use the tetrahedron method when computing the density of states, check out this paper on exactly that topic! In short, other approaches (e.g. Gaussian smearing) will ...
- 6,941
11
votes
How to make a k-point convergence test for a bulk structure with a lower k-point in the z-direction?
If you have already obtained satisfactory convergence with a (relatively) sparse k-point grid, there is no motivation to go for a denser grid. So if you have already achieved convergence with 12x12x4, ...
- 2,212
11
votes
Monkhorst-Pack, Gamma-centred and gamma only
Gamma Only:
A k-point mesh (grid) only includes (samples) the gamma point of the Brillouin zone.
Gamma Centred:
A k-point mesh (grid) that is centred around the gamma point of the Brillouin zone, and ...
- 1,829
11
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 ...
- 3,038
11
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 ...
- 111
11
votes
Accepted
Number of KPOINTS in irreducible part of Brillouin zone
It is not necessary to care about the total energy versus the number of k points in irreducible reciprocal space, which is closely related to the symmetry of the investigated structure. Of course, you ...
- 14k
10
votes
Is total energy difference lower than 1 meV/atom good enough for k-point convergence?
When using a method like density functional theory we have to consider the accuracy of (i) the numerical solution of the problem and (ii) the physical model we use.
The convergence you are refering to ...
- 10.4k
10
votes
Accepted
Which properties of a material calculated using density functional theory are affected by smearing?
In brief, it will influence the electronic energy and thereby all properties derived from that. Too small a smearing width and you might have trouble converging the self-consistent field. Too large ...
- 6,941
10
votes
Accepted
Validity of interpolation for density of states?
Calculating densities of states is a tricky problem, as you correctly recognized. The density of states is:
$$
\tag{1}
g(E)=\sum_{n}\int\frac{d\mathbf{k}}{(2\pi)^3}\delta(E-E_{n\mathbf{k}}),
$$
where $...
- 10.4k
9
votes
Is it okay to take a cubic Monkhorst-Pack k-mesh for a non-cubic supercell in a DFT calculation?
It will obviously affect the calculation time, which would be the only reason I would discourage you based on my knowledge. It should not harm anything to continue with a higher symmetry k-mesh, but ...
- 10.2k
9
votes
How to make a k-point convergence test for a bulk structure with a lower k-point in the z-direction?
I agree with the answer provided by Xivi76. I just wanted to add that some codes have a very nice functionality that facilitates convergence: rather than explicitly writing out a $\mathbf{k}$-point ...
- 10.4k
9
votes
k-points convergence for special quasirandom structures (SQS) of the same material containing different # of atoms
Very good question.
I think that when you select one of the many different disordered structures as been a representative one, that structure is not disordered anymore, it is an structure as any ...
- 19.2k
9
votes
mBJ-LDA band structure calculation using VASP
If you give the explicit points in the KPOINTS file in VASP for a band structure calculation, for example as required for hybrid functionals, the bands will only be calculated at the explicit $\mathbf{...
- 10.4k
8
votes
How to know optimal K-points grid values for good DFT calculation?
You can upload your structure [many formats are supported] into the following website to generate the input file for your Quantum Espresso calculation.
Materials Cloud Website
There are three ...
- 14k
8
votes
Accepted
How to generate KPOINTS file for HSE06 band-structure calculations?
In order to generate the k-path for any material, the first thing to know is the crystal system (a,b) of it. This information can be obtained experimentally via X-ray diffraction analysis, form the ...
- 19.2k
8
votes
"A dense k mesh of 40,000 k points was used in the Brillouin zone". How is this number obtained?
The computational content of the cited paper includes two parts:
DFT calculations (such as band structures) with QE;
Transport calculations (such as Seebeck coefficients) with BoltzTraP based on DFT ...
- 14k
8
votes
Physical interpretation of k-points
In order to answer this, I will introduce k-points in two different ways.
1. Bloch's theorem
The usual approach to introducing k-points is to start with Bloch's theorem. In a periodic potential $V$, ...
- 4,382
7
votes
How to generate KPOINTS file for HSE06 band-structure calculations?
To add to ProfM's answer, you can generate lists of k-points along high-symmetry paths in the Brillouin zone using XCrySDen. Open your structure (you can format it as a XYZ file) and go to the Tools ...
- 2,931
7
votes
Running Quantum ESPRESSO calculations in Google Colab
You can check this article I've written on doing the same, but without using the ASE python library. Just create the input file as you would normally do along with the pseudo-potential files and keep ...
- 4,278
7
votes
How to make a k-point convergence test for a bulk structure with a lower k-point in the z-direction?
As far as my knowledge this a relationship between k-points and lattice constants values. I'll give you an example of a layered hexagonal material WS2:
Lattice constants : ...
- 5,531
7
votes
How to know optimal K-points grid values for good DFT calculation?
To build on the other good answers here, there are also numerous ways to generate k-point grids.
The most common method (described here) is Monkhorst-Pack, which is the method you'll see in typical ...
- 1,461
7
votes
Accepted
Why is Energy Cut-off and K-Point Convergence necessary in LCAO-based codes like SIESTA?
The k-point discretization has the same meaning in plane wave codes as LCAO based codes. In fact, it has the same meaning in all DFT related codes. It defines the integration of the Brillouin zone. ...
- 1,814
7
votes
Doubt about K point selection for 2x2x1 supercell
The KPOINTS have an inverse relationship with the real space lattice vectors. In either way, you won't go wrong. I would prefer to test it using 1x1x2, 1x1x3, 1x1x4, etc. This is simply because your c ...
- 930
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