Questions tagged [k-points]

Questions regarding k-points in crystal geometric settings.

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8
votes
1answer
61 views

Valleys and time reversal symmetry (Zeeman effect)

Right now I'm focused on transition metal dichalcogenides. These compounds in the Brillouin zone have valleys in the valence band and in the conduction band at points K and -K. From what I've seen of ...
12
votes
1answer
503 views

What does occupations='tetrahedra' mean in Quantum ESPRESSO?

I am trying to understand Quantum ESPRESSO input file, line by line. So far everything seems pretty easy to understand. However, I do not know what ...
13
votes
3answers
389 views

How to generate the high symmetry paths for band structure calculations?

Suppose I want to calculate the band structure of a material system along a specific high symmetry path in the Brillouin Zone. If the point group of the system is given, how can I easily compute the ...
11
votes
1answer
231 views

Why is Energy Cut-off and K-Point Convergence necessary in LCAO-based codes like SIESTA?

I am new to DFT-simulation and I wish to understand how it works behind the scene. As the title suggests I don't understand why LCAO-based codes have to define K-points and cut-off energies. I ...
6
votes
1answer
74 views

“A dense k mesh of 40,000 k points was used in the Brillouin zone”. How is this number obtained?

In publications, I usually see the statement "A dense k-mesh of 40,000 k-points was used in the Brillouin zone". An example of this is in this paper. But in the paper they have ...
11
votes
1answer
236 views

Number of KPOINTS in irreducible part of Brillouin zone

I want to investigate the comparison of Total Energy per cell with respect to the number of KPOINTS in the irreducible part of the Brillouin zone but I do not know ...
6
votes
2answers
49 views

Does SOC band structure calculations require higher number of k-grids?

In so many papers I see that they carry out soc band structure calculations with much higher kgrid than used for the geometry optimization. Whats the logic behind that?
3
votes
2answers
97 views

Energy per unit cell in NWChem differs for different supercells despite the same k-points density

I try to compute the unit cell energy of the $\ce{Ti2CO2}$ MXene with NWchem. Computing the 1x1 supercell with 4x4x1 K-points grid I got -1875 Ha. Computing the 2x2 supercell with 2x2x1 K-points grid ...
10
votes
1answer
167 views

How to analyze the band symmetry with Quantum ESPRESSO?

This question is related to this paper: J. Phys. Chem. Lett. 2017, 8, 13, 2999–3007 The above figure shows symmetry analysis for the band structure. The author writes: The band symmetry and parity ...
9
votes
2answers
102 views

Validity of interpolation for density of states?

A density of states (DoS) curve seems like an example of a curve for which curve fitting doesn't seem to make sense, or does it? How could we interpolate on such a curve, given that we got the curve ...
13
votes
1answer
217 views

Is total energy difference lower than 1 meV/atom good enough for k-point convergence?

How much energy difference could be considered as tight convergence? Is total energy difference lower than 1 meV/atom good enough for kpoint convergence for total energy calculation?
7
votes
1answer
242 views

k-points: Odd vs. Even

As mysterious as k-points are, why is there a cut-off for an odd and even k-mesh preference? On the VASP wiki page titled, "Number of k points and method for smearing", they say results when ...
10
votes
5answers
2k views

How to know optimal K-points grid values for good DFT calculation?

I am doing DFT calculations with pw.x executable in Quantum Espresso. For this we have to choose right K-points grid in order to perform error-less calculation. But I have no idea about how can I ...
9
votes
1answer
397 views

Monkhorst-Pack, Gamma-centred and gamma only

Sorry if this question is too simple for this community but I still couldn't find an answer to it. Do gamma-centred and gamma only grid mean the same thing? If not, what's the difference? How do they ...
11
votes
1answer
91 views

adaptive k-mesh

Are there any known codes or scripts to generate an adaptive k-mesh for DFT calculations? For example, I'd like to make the k-mesh near the $\Gamma$ point (e.g., half the zone) more denser ($20\...
7
votes
2answers
73 views

Input constraints while comparing different DFT calculated properties for the same material but different atomic arrangement

Let's consider a fictitious AB type binary alloy. AB is known to exist in a B2 type ordered ...
11
votes
1answer
292 views

Increasing supercell size to increase K-points sampling

Suppose I have a system with a property that is highly dependent on the density of k-points, namely the dielectric function. Using a small supercell, say with 4 atoms, I've reached the maximum allowed ...
11
votes
2answers
151 views

Which properties of a material calculated using density functional theory are affected by smearing?

Smearing (smearing width $\sigma$, to be precise) has always been confusing. I understand what it is but can't pin it down when it comes to DFT calculations. Should it be converged like k-points and ...
8
votes
2answers
126 views

k-points convergence for spin polarised vs non-polarised DFT calculations

Spin-polarised calculations come at a computational cost and I tend to take ISPIN = 2 only after I'm done with a proper initial relaxation of the structure, so the ...
7
votes
0answers
238 views

Calculating band structure with HSE using Open_grid (Quantum ESPRESSO) [closed]

I have executed the SCF calculation and obtained the results. After which I used kmesh.pl to extract k-points. I was able to run wannier calculations but there was an error Checking info from wannier....
12
votes
2answers
640 views

mBJ-LDA band structure calculation using VASP

I tried to create a band structure with the mBJ-LDA method using VASP. I found information that the KPOINTS file should be created according to the "0-weight (...
9
votes
3answers
672 views

How to generate KPOINTS file for HSE06 band-structure calculations?

I have had a look at the example of Silicon provided here in the WIKIVASP website, and I noticed that the KPOINTS file used for ...
10
votes
1answer
174 views

Is it okay to take a cubic Monkhorst-Pack k-mesh for a non-cubic supercell in a DFT calculation?

Assume that the numbers of k-points in each direction are sufficient. Example - Lengths of lattice vectors: $2\: 2\: 4$ Required k-mesh: $9\times 9\times 5$ Would a $9\times 9\times 9$ k-mesh work? ...
9
votes
1answer
295 views

How to derive the k-path for monoclinic lattice structure?

Good afternoon all, My post is inquiring about the mathematical derivation behind the Monoclinic crystal structure (c axis unique). The Brillouin zone (BZ) I really would like to derive is shown below:...
12
votes
4answers
566 views

How to make a k-point convergence test for a bulk structure with a lower k-point in the z-direction?

Let's say I want to make k-point convergence test for graphite. And let's say it converges at 12x12x4. Do I first need to do a k-point convergence test for equal k-points on xyz directions then make ...
16
votes
3answers
804 views

Running Quantum ESPRESSO calculations in Google Colab

So one big problem I experience in doing calculations with Quantum ESPRESSO is that many calculations require a lot of computing power: you need large RAM capacities and powerful processors especially ...
16
votes
1answer
112 views

k-points convergence for special quasirandom structures (SQS) of the same material containing different # of atoms

For an ordered crystal, we generally converge the k-mesh resolution for a primitive cell or other smaller supercells. We then use this resolution for any other size of the supercell for the same ...