Questions tagged [k-points]

Questions regarding k-points in crystal geometric settings.

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19 votes
3 answers
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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 ...
jboy's user avatar
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18 votes
4 answers
4k 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 ...
beginner's user avatar
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17 votes
1 answer
1k views

Physical interpretation of k-points

What is the Physical interpretation of the k-points used in ab initio calculations? Why must the number of k-points be optimized rather than just using some large fixed number of them?
Maulesh VALA's user avatar
16 votes
1 answer
175 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 ...
Hitanshu Sachania's user avatar
15 votes
1 answer
6k 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 ...
Bereau's user avatar
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14 votes
2 answers
3k 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 (...
M_Fisher's user avatar
  • 611
14 votes
1 answer
1k views

Doubt about energy convergence with different k points

During the convergence test of k points, I observed my energy start increasing instead of decreasing. I am doubtful is this correct or I am doing something wrong. can I take the appropriate K point in ...
poonam sharma's user avatar
13 votes
5 answers
9k 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 ...
UJM's user avatar
  • 2,601
13 votes
4 answers
3k 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 ...
Taavi's user avatar
  • 131
13 votes
1 answer
2k 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 ...
RedGiant's user avatar
  • 335
13 votes
1 answer
641 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?
Barix's user avatar
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12 votes
1 answer
1k 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 ...
Anibal Bezerra's user avatar
11 votes
3 answers
2k 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 ...
Chi Kou's user avatar
  • 5,803
11 votes
2 answers
787 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 ...
Hitanshu Sachania's user avatar
11 votes
1 answer
730 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 ...
Shalini's user avatar
  • 1,605
11 votes
1 answer
2k 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 ...
Brentdb's user avatar
  • 113
11 votes
1 answer
784 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 ...
Jack's user avatar
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11 votes
1 answer
220 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\...
Xiaoming Wang's user avatar
10 votes
2 answers
257 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 ...
Hitanshu Sachania's user avatar
10 votes
1 answer
234 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? ...
Hitanshu Sachania's user avatar
10 votes
1 answer
1k 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:...
abed haidar's user avatar
9 votes
2 answers
472 views

Why do we need to use fake k-points when doing HSE band structure in VASP?

I want to know why we need fake k-points in HSE band structure calculation? I mean why we can't take a simple high symmetric path like we do in PBE calculation?
Himanshu Sharma's user avatar
9 votes
2 answers
560 views

Doubt about K point selection for 2x2x1 supercell

I have one doubt about K points selection for a supercell. I construct one 2X2X1 supercell with 64 atoms having a=11.19, b=11.19, c=5.59. For checking K points convergence test with energy should I ...
poonam sharma's user avatar
9 votes
2 answers
337 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 ...
Hitanshu Sachania's user avatar
8 votes
1 answer
296 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 ...
Hydrogen's user avatar
  • 159
8 votes
1 answer
1k 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 ...
Hitanshu Sachania's user avatar
8 votes
1 answer
481 views

How could I fold a specific high symmetry point to the Gamma point?

How could I get the Brillouin Zone of 2*2 supercell? I tried to use see k-path website, but when I upload a supercell, it still generates the Brillouin Zone of the unit cell. What I want to do is to ...
Jack's user avatar
  • 2,027
8 votes
1 answer
295 views

Generating a Gamma centered uniform k mesh in SIESTA DFT

The SIESTA DFT software provides to incorporate a Monkhorst-Pack k grid in DFT calculations. However to use the results with the BoltzTraP2 software, a Gamma centered k-grid with uniform distribution ...
PBH's user avatar
  • 2,653
8 votes
1 answer
328 views

What is the M-point of an orthorhombic crystal structure?

In this paper, they have plotted the band structure of orthorhombic $\ce{CsPbI3}$ using Wein2k. The k-path given here is Γ—X—R—Z—Γ—X—R—A—M—X, but I cannot find the M point in the orthorhombic crystal ...
Wonder's user avatar
  • 181
8 votes
1 answer
357 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 ...
Carmen González's user avatar
7 votes
2 answers
101 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 ...
Hitanshu Sachania's user avatar
7 votes
2 answers
937 views

Can someone guide me on how to get the k-point file for a VASP simulation?

I have a system with box dimensions of 21.0 * 21.0 * 80.0 for x,y and z directions. How may I generate the KPOINTs mesh for this system for VASP simulation? Any reference on this is hugely appreciated....
Xdrake's user avatar
  • 541
7 votes
1 answer
538 views

Monkhorst – Pack sampling: How many k points one should take

Reference: Density Functional Theory: A Practical Introduction, David Sholl, Janice A. Steckel, Chapter 3, Page No. 59 A useful rule of thumb is that calculations that have similar densities of k ...
147875's user avatar
  • 663
7 votes
1 answer
561 views

Minimum number of kpoints for calculation of properties of nanoparticles in vasp

I am a little confused about what should be the correct number of kpoints that I wanna use. I am currently working on a small cluster so picking a high value(even around 10) gives me a memory fault. ...
Parmeet Singh EP 066's user avatar
7 votes
0 answers
359 views

How to choose K point for a super cell [closed]

I have been told to use VASPKIT in order to obtain the KPOINTS, but VASPKIT only works for Primitive cell and I am currently using a super cell. The super cell has a repeated primitive cell about one ...
Parmeet Singh EP 066's user avatar
7 votes
0 answers
796 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....
Hepsibah Priyadarshini.C's user avatar
6 votes
2 answers
245 views

Number of k-points for unit and super cell

I am just new with solid state calculation and would like to know one thing. Why is plane wave basis set is good for 1s and 2s orbitals, but for higher convergence is poor? Why is it better to use ...
Alexander Teryahskin's user avatar
6 votes
1 answer
195 views

About high-symmetry points in the first Brillouin zone of space group R-3m

I want to figure out the high-symmetry points in the first Brillouin zone of space group R-3m (166). For example, there are points K and M just like the bandstructure in this paper. But I can't figure ...
MathJacky's user avatar
6 votes
1 answer
224 views

Confusion regarding specifying a k-point path for phonon dispersions/bandstructure plots

I have been trying to obtain a plot of the phonon dispersion of a BCC metal using Quantum Espresso. In the literature it seems that a commonly reported path is ...
aQuarkyName's user avatar
6 votes
2 answers
119 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?
user avatar
6 votes
1 answer
557 views

How to transform the k coordinate into the k path used in the band structure?

When drawing the band structure, I need to transform the coordinate of k-points into a k-path, but I am not sure what the formula is. I checked the result of siesta,...
Jack's user avatar
  • 2,027
6 votes
0 answers
191 views

How to find the reduced coordinates of reciprocal lattice vector which defines the kslice plane in first brillouin zone? [closed]

I am trying to get the Fermi contour lines of an FCC crystal system. For this, I am trying to use the wannier90 program. I have already done the wannierzation part successfully. Now I am trying to get ...
UJM's user avatar
  • 2,601
5 votes
1 answer
222 views

VASPKIT and SeeK-path recommend different paths. Which one to choose?

I want to get the phonon density of states for a monolayer MoS2. For this, I need phonon dispersion curves, and to choose a path where to compute phonons. VASPKIT recommends Γ-M-K-Γ SeeK-path ...
Vladislav Gladkikh's user avatar
5 votes
1 answer
3k views

Reciprocal lattice and k-lattice belong to different groups in VASP

I am trying to do geometry optimization of TiO2 with VASP. Here is the POSCAR file, which I get from the Materials Project. ...
Jack's user avatar
  • 2,027
5 votes
1 answer
170 views

How to add a break into CASTEP k-point path

I am trying to produce a band structure for TiO2, with the cell file shown below: ...
Rory Ward's user avatar
  • 121
5 votes
1 answer
235 views

k-path for phonon band structure

I have observed in research papers that the k-path chosen for electronic band structure and for phonon band structure to be different. I am currently using VASPKIT in order to obtain the path for ...
Parmeet Singh EP 066's user avatar
5 votes
0 answers
68 views

Optical properties using ESPRESSO's epsilon.x

Currently I'm using epsilon.x from Quantum ESPRESSO to analyse optical properties of metallic alloys. I'm getting a wiggling curve for the dielectric function. For the imaginary part of dielectric ...
Anibal Bezerra's user avatar
4 votes
2 answers
654 views

What's the meaning of k-points with weight zero?

In a post from the Quantum Espresso mailing list, a user suggests adding k-points with weight zero to an SCF calculation as a workaround to allow bandstructure to be computed using a hybrid functional....
Camilla's user avatar
  • 2,119
4 votes
2 answers
196 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 ...
user36313's user avatar
  • 700
4 votes
0 answers
44 views

supercell nscf kpoints for optical properties

I am calculating the optical properties of 200 atoms supercell with quantum espresso. What is the approximate number of the nscf kpoints (nk nk nk)should I start with, to avoid lengthy kpoints ...
hakou elhaj's user avatar