Questions tagged [quantum-espresso]

Questions related to the open source materials modeling framework, Quantum Espresso.

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29 votes
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Quantum ESPRESSO vs VASP

We know that both Quantum ESPRESSO and VASP can perform lots of different kinds of simulations of materials. But what can VASP do that Quantum ESPRESSO can not, and vice-versa?
Anibal Bezerra's user avatar
24 votes
2 answers
7k views

What are some good band-structure/DOS plotting tools/styles?

I am currently using p4vasp for drawing DOS and band-structure plots, but it is not much handy in modifying the OUTPUTS. Could you please suggest any other good software or tools for that?
Chi Kou's user avatar
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23 votes
3 answers
934 views

How to do periodic DFT calculations using Quantum ESPRESSO?

I have only done quantum mechanical computations using non-periodic wavefunctions. I'd like to try to periodic-wavefunction density functional theory. Quantum ESPRESSO seems like a good package ...
Cody Aldaz's user avatar
  • 7,997
23 votes
1 answer
2k views

Why is the band structure of a supercell more dense than for simple cell?

In order to do DFT calculations of metallic alloys, the start point is a supercell, whose atoms are changed to match the desired stoichiometry. Gold and Silver, for example, both have FCC structure. ...
Anibal Bezerra's user avatar
21 votes
9 answers
9k views

How to master Fortran with minimal effort?

Fortran language is used in many first-principles matter modeling codes, such as VASP and QE. These codes usually include many ...
Jack's user avatar
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21 votes
4 answers
2k views

Is it possible to calculate the Curie temperature for magnetic systems?

Using DFT calculations we can know the electronic and magnetic property of the system at 0 K. I am wondering if there is any computational method to know the curie temperature of magnetic materials? ...
UJM's user avatar
  • 2,591
21 votes
3 answers
4k views

k-points and ENCUT convergence tests before or after relaxation?

Let's say I want to relax a structure using VASP. K-points and ENCUT convergence tests must be conducted before or after relaxation? and which tags should be ...
Chi Kou's user avatar
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21 votes
2 answers
5k views

What is the difference between Ultrasoft, ONCV and PAW Pseudopotentials? Which is better for a spin-orbit coupled calculation?

I am trying to do spin-orbit coupled calculations for various topological insulators. I have found papers using Quantum Espresso with ONCV pseudopotentials and papers using VASP with PAW ...
Ashique Lal's user avatar
  • 1,601
20 votes
2 answers
11k views

Calculating HSE06 band structures on Quantum ESPRESSO

I am currently trying to figure out how to compute band structures for my system, using the hybrid functional HSE06. I'm doing this on Quantum Espresso. As I understand, there are a handful of ways to ...
livars98's user avatar
  • 2,456
20 votes
2 answers
1k views

Norm-Conserving or Ultrasoft, which pseudopotential to choose?

Ultrasoft pseudopotential (USPP), in general, requires a lower energy-cutoff to the plane waves when compared to Norm-Conserving ones (NC). On the other hand (at least with Quantum ESPRESSO) the ...
Anibal Bezerra's user avatar
20 votes
1 answer
183 views

What is the importance of electron interaction on dielectric response of crystals?

After obtaining the Kohn-Sham orbitals from a plane-wave-based self-consistent-field calculation, the dipole matrix elements could be calculated in order to determine electro-optical properties such ...
Anibal Bezerra's user avatar
19 votes
3 answers
2k 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 ...
jboy's user avatar
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18 votes
2 answers
9k views

What is nscf calculation in Quantum ESPRESSO?

I have been using 'nscf' for DOS calculation since it is faster and therefore possible to use a higher kpoints. But why is it faster? why not use it in the place of 'scf'?
Ashique Lal's user avatar
  • 1,601
18 votes
2 answers
561 views

Calculating binding energy between two systems

Regarding the calculation of binding energy of molecular absorption on graphene, for which this has been discussed before, the process of calculating $E_{AB}$ is fairly straight forward, i.e., it is ...
Shahid Sattar's user avatar
17 votes
1 answer
1k views

How does the mBJ potential give an accurate band gap as compared to LDA and GGA?

I am not able to understand the literature on how the modified Becke-Johnson(MBJ)$^{[1]}$ potential gives an accurate bandgap. Can someone please help? Thank you. The formula for the potential can be ...
sonia rani's user avatar
17 votes
1 answer
1k views

Are there problems with the Tran-Blaha modified Becke-Johnson potential (mBJ, a.k.a. TB09) in Quantum ESPRESSO?

I have used the modified Becke-Johnson (mBJ) exchange potential before, as it was developed and implemented in Wien2K by Fabien Tran and Peter Blaha (1). In 2013, Éric Germaneau et al. implemented mBJ ...
epalos's user avatar
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16 votes
1 answer
975 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
15 votes
1 answer
384 views

Can GW-BSE quasiparticle calculations only be run on norm-conserving pseudopotentials (NCPPs)? If so, why not?

I've read in some texts that GW-BSE quasiparticle calculations have only been implemented on Norm-conserving Pseudopotentials (and not Ultra-soft or PAW PPs). Is there a conceptual reason for this? I ...
livars98's user avatar
  • 2,456
14 votes
3 answers
6k views

Should I connect 2-3 laptops to form a supercomputer?

I have recently started to use Quantum ESPRESSO for evaluating different properties of ZnSe Quantum Dots. But I currently don't have access to any cluster and as I am increasing the size of ...
Parmeet Singh EP 066's user avatar
14 votes
2 answers
3k views

When should spin polarized calculations be done?

Should the presence of a d block element in the unit cell mandate the need for performing spin-polarized calculations? I wanted to find out the DOS, PDOS, and the band structure. I'm new to DFT and I'...
Anoop A Nair's user avatar
  • 4,458
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
  • 2,591
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
2 answers
1k views

Getting different total magnetic moment in 'scf' and 'vc-relax' calculations in Quantum ESPRESSO

I am performing a spin polarized DFT calculations in Quantum Espresso on a Co2MnSi ferromagnetic crystal. For this I have performed these steps: 1) Performed ...
UJM's user avatar
  • 2,591
13 votes
2 answers
3k views

How to calculate the effective mass from DFT band calculations?

One of the properties used in Solid State Physics, and specially in semiconductor physics, is the effective mass. It can be calculated from the energy dispersion relationship. The simple form, for ...
Camps's user avatar
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13 votes
1 answer
1k views

How do we know how much computational power is required for a particular calculation?

So I am super new, although I have gotten the hang of using DFT in Quantum Espresso. I am having a problem with running the calculation for 1.6 nm ZnSe quantum dot. I haven't even gotten to ...
Parmeet Singh EP 066's user avatar
13 votes
1 answer
843 views

Si energy band values are not matching with literature values

I have performed the DFT calculation for Silicon in Quantum ESPRESO. I have tried to calculate the electronic band structure, the shape of wiggles of bands are mostly matching but the energy values ...
UJM's user avatar
  • 2,591
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
1k views

Why is the Nonequilibrium Green’s function (NEGF) method for quantum transport not implemented in plane wave codes like VASP and Quantum Espresso?

DFT codes like Siesta, QuantumATK, Questaal, and Smeagol having localized basis sets have NEGF implementations available. But not in plane wave codes like VASP and Quantum Espresso. Why is it so?
Thomas's user avatar
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13 votes
2 answers
1k views

Deciding the number of CPUs for a DFT calculation for band structure in Quantum ESPRESSO?

If I am using Quantum ESPRESSO for bandstructure calculations, how can I know the number of CPUs necessary for such a calculation? I deal mostly with ternary transition metal oxides which have at ...
Smarak Rath's user avatar
13 votes
1 answer
3k views

How to do spin polarization calculations using Quantum ESPRESSO?

I am currently new to DFT calculations in Quantum ESPRESSO. Though, I have read some research papers for determining spin polarization and Half-metallicity in certain Heusler alloys. These research ...
UJM's user avatar
  • 2,591
13 votes
1 answer
673 views

Parallelization levels on Quantum ESPRESSO

Quantum ESPRESSO presents several levels of parallelization, including worlds, images, polls, and so on. However, there is a very intricate (and not clear to me) relationship between k-point sampling, ...
Anibal Bezerra's user avatar
12 votes
3 answers
2k views

How can I submit jobs to an HPC scheduler?

It is my first time trying to use an HPC system and I am a bit overwhelmed. I have gone through a course on using HPC systems on Coursera and have a basic idea about using Linux. Could you guys tell ...
Parmeet Singh EP 066's user avatar
12 votes
2 answers
689 views

Computational Speed vs multicores

Why is that increasing the number of cores (openMP) in a computation does not decrease the duration of the process? Is it due to consecutive approximation? I took a very simple system of Cu in FCC ...
147875's user avatar
  • 663
12 votes
2 answers
9k views

What is the difference between DOS and PDOS?

I'm new to DFT. Can you please help me to understand DOS and PDOS (projected density of states) in simple wording? I only want to know some basics of these terms and how they are linked to DFT.
Areej Sahar's user avatar
12 votes
1 answer
7k views

When should "vc-relax" be performed over "relax" calculations in Quantum ESPRESSO?

I'm new to Quantum ESPRESSO and I have read that there are several scenarios when relax calculations are preferred over vc-relax calculations, for example in maintaining vacuum while modelling surface....
Anoop A Nair's user avatar
  • 4,458
12 votes
2 answers
2k views

How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?

I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
UJM's user avatar
  • 2,591
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
12 votes
2 answers
689 views

Recommended code to do XAS/XES/RIXS calculations with?

I am a grad student looking to simulate several XAS/XES and potentially RIXS spectra for some strongly correlated metal-oxides. The materials in question will likely require solving the Bethe-Salpeter ...
Haru Fujimura's user avatar
12 votes
1 answer
422 views

What is the best program to manipulate numerical DFT wavefunctions to calculate custom matrix elements?

For pedagogical reasons, I am looking for ways to calculate quantum-mechanical quantities such as $\langle m | \dot{m}\rangle, \langle m | \dot{n}\rangle, \langle m | \ddot{n}\rangle$ using ...
TribalChief's user avatar
  • 2,321
12 votes
1 answer
1k views

How many GB of RAM would be needed for VASP to evaluate optical properties of a material?

Even though it is a powerful tool, Quantum ESPRESSO's hardware requirements are very high. For instance, to evaluate optical properties, even for structures with tens of atoms, Quantum ESPRESSO can ...
Anibal Bezerra's user avatar
11 votes
2 answers
1k views

Is there an energy gap correction factor that needs to be used in DFT calculations?

I am a beginner and have performed the DFT calculation in Quantum ESPRESSO for calculation of the direct and indirect bandgap of Silicon. I found the indirect bandgap to be 0.6551 eV. Now, I have ...
UJM's user avatar
  • 2,591
11 votes
2 answers
2k views

Plotting density of states of Fe(BCC) using Quantum ESPRESSO

I have run the DFT calculation and plotted DOS of Fe(BCC) in Quantum ESPRESSO. I have attached the plot: (click on image to see clearly) But It's a wrong plot as it is not matched with the referenced ...
UJM's user avatar
  • 2,591
11 votes
1 answer
1k views

How to calculate the energy of conduction band and valence band with respect to vacuum in quantum espresso?

I was able to calculate band energies in quantum espresso. How to convert them to values that are in terms of difference from vacuum energy?
Ashique Lal's user avatar
  • 1,601
11 votes
1 answer
1k views

Is the "Final Magnetic moment" in the materials project repository same as the "total magnetization" value in Quantum ESPRESSO output files?

I'm quite new to spin-polarized DFT and have been trying to study $BaVSe_{3}$ which is ferromagnetic (with a Final Magnetic Moment of 0.052 Bohr Mag) as per the Materials Project repository [picture 1]...
Anoop A Nair's user avatar
  • 4,458
11 votes
1 answer
295 views

Is there any software that can generate the electronic DOS of GaAs?

I want to calculate the density of states of GaAs conduction band (preferably each valley like Gamma, L and X). Is there any software available where I can easily generate DOS? Has the DOS of GaAs ...
Tom Jhonko's user avatar
11 votes
1 answer
753 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
  • 14.9k
11 votes
1 answer
322 views

Geometrical Optimization not converging, where am I going wrong?

I am trying to obtain the optical properties of ZnSe Quantum Dots, the problem is that my geometrical optimization is not converging. I used VESTA to create the structure(there is a photo in the ...
Parmeet Singh EP 066's user avatar
11 votes
1 answer
231 views

Are there any other options beyond increasing the k-sampling and the number of unoccupied bands, to achieve better results?

I am trying to determine the optical properties of bulk Aluminium and related alloys using Quantum ESPRESSO. I am using both the epsilon.x and the simple.x modules to get wavelength-dependent ...
Anibal Bezerra's user avatar
11 votes
1 answer
404 views

How do I predict the structure of a nanoparticle with Calypso and Quantum ESPRESSO?

I want to create a nanoparticle of CuO and predict it's structure. I've done unit cell relaxation with Quantum ESPRESSO. One tool to predict nanocluster structure is Calypso which is PSO-based. I'm ...
Shafayet Rahat's user avatar
11 votes
1 answer
87 views

How can I properly attach ligands to a surface?

The main aim of my venture is to study the effect of the presence of surface ions on the band structure of Si slab using Quantum ESPRESSO. I've tried to use iQmol to attach ligands to the surface. The ...
Atom's user avatar
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