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15 votes

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

'vc-relax' and 'relax' are two quite different functionalities of the PW module. 'vc' stands for 'variable cell', so the cell shape (angles and length) as well as the atomic coordinates are optimized. ...
Xiaoming Wang's user avatar
11 votes
Accepted

Structure relaxation of a thin film structure in VASP

Should I turn the ISYM = 0 to also change the shape of the unit cell during the structure relaxation? In essence, you are asking how to build a slab model. One special point is that you should add a ...
Jack's user avatar
  • 15.2k
11 votes
Accepted

Pressure applied DFT calculations in Quantum ESPRESSO

I would not recommend applying external hydrostatic pressure by changing the lattice parameter by hand. This is because fixing the lattice parameters by hand may lead to the incorrect structure. For ...
ProfM's user avatar
  • 11.1k
9 votes

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

Edit: This no longer seems to be the issue, as the atomic positions are apparently essentially unchanged, per @KevinJ.M.'s comment. I will nonetheless keep the answer here because it is still ...
Andrew Rosen's user avatar
  • 7,391
9 votes
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Getting different total magnetic moment in 'scf' and 'vc-relax' calculations in Quantum ESPRESSO

Looking at your input and output files, I think the most likely explanation is a different local minimum in the energy, as mentioned by Andrew in the comments. If you look at the final scf step in the ...
Kevin J. May's user avatar
  • 3,161
8 votes

Should I do vc-relax with nspin=2 in Quantum Espresso for magnetic samples?

It is a bit difficult to answer this question, due to the information provided. If you are a beginner, using vc-relax will have its pros and cons. With regards to using nspin=2: Recall that when you ...
epalos's user avatar
  • 4,869
8 votes
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What's the Difference between Lattice Statics and Lattice Dynamics?

Lattice statics refer more to the minimum energy lattice structure such as spacegroup, lattice constant, bond distances, or any other property you can derive from a geometric standpoint on that ...
Tristan Maxson's user avatar
8 votes
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Why volume of unit cell is not the same as cubing the lattice constant?

Please read the pw.x documentation on the Bravais lattice index (ibrav). The cell vectors for the primitive cell corresponding ...
leopold.talirz's user avatar
7 votes

How to do lattice optimization, encut optimization and Kpoint optimization in VASP?

You can start with this bash script for Aluminum to begin Note: Make sure to fix two quantities while changing third one among INCAR,...
Pranav kumar's user avatar
  • 4,243
7 votes

How to restart an interrupted Quantum ESPRESSO calculation?

You need to have prepared for this beforehand. You need to write out the wavefunctions in a place that is accessible for the new run to absorb in, and so forth. https://www.quantum-espresso.org/Doc/...
naturallyInconsistent's user avatar
6 votes
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How to calculate lattice parameter?

In your output file, there should be a line at the beginning saying "crystal axes: cart. coord. in units of alat)" like the following: ...
Abdul Muhaymin -Free Palestine's user avatar
6 votes

Should alat value be used as it is in calculation or multiplied with CELL_PARAMETERS value?

alat works like a scale factor. So, as pointed out by naturallyInconsistent, you can use A=5.95*1.07708030 because in QE, ...
Abdul Muhaymin -Free Palestine's user avatar
6 votes
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How can I perform a cell shape relaxation in a specified direction using VASP?

As of July 2023 at least, VASP doesn't have such a functionality (see this post). I know of two options (I've used the first one frequently when relaxing slab structures while keeping the vacuum axis ...
CW Tan's user avatar
  • 1,316
5 votes
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Significant external pressure in non-SCF calculation results

The energy, pressure, forces etc are only accurate for a converged K-point grid. When you do a band structure calculation, you are sampling a tiny subset of reciprocal space and e.g. pressure will ...
Tyler Sterling's user avatar
5 votes

Meaning of lattice parameters in vc relax calculations

From documentation ...
Pranav kumar's user avatar
  • 4,243
5 votes
Accepted

How to get rotation matrix elements from root integer notation?

$\sqrt{3}$ Case $ \left( \sqrt{3} \times \sqrt{3}\right)R30$ is a short way of representing a supercell in Woods notation (1, 2), which essentially means that each of the basis vectors of the ...
Vandan Revanur's user avatar
5 votes

Cu FCC vc-relax method error

ibrav = 2 in Quantum Espresso gives an fcc Bravis lattice, as mentioned in the answer by Tyberius, with the lattice vectors: ...
Brandon Bocklund's user avatar
5 votes

Cu FCC vc-relax method error

As the error message states, your atoms 1 and 2 are related by translation vectors, so you can't specify both of them. Note the lattice vectors used for an FCC system in QE: 2 cubic F (fcc) ...
Tyberius's user avatar
  • 15.5k
5 votes

Pressure applied DFT calculations in Quantum ESPRESSO

In your case, the crystallographic axes look to be equivalent, so just use 'relax' to start with. This will fix the lattice constants (equivalent to applying pressure) but will move the atoms around - ...
Xivi76's user avatar
  • 2,392
4 votes

Should I do vc-relax with nspin=2 in Quantum Espresso for magnetic samples?

If the system is magnetic you need to use nspin=2. You can use any pseudopotential, unless you want to see SOC, in which case you need to use a fully relativistic ...
4 votes
Accepted

In VASP, which option is better for monolayer relaxation: ISIF=3 or ISIF=4?

When dealing with monolayers, I have found that using the ISIF=4 tag is better and is less time-consuming. As mentioned in Vaspwiki, it allows the relaxation of ...
Chi Kou's user avatar
  • 5,833
3 votes
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Smearing and charge balance for tungsten with interstitial oxygen in Quantum ESPRESSO

There are many reasons behind not converging. Sometimes structure doesn't converge if you describe them wrong. So, in my opinion, the best way to converge a structure is to study it clearly. Moreover, ...
Shafayet Rahat's user avatar
3 votes

What parameters have to converge before doing a relax calculation?

Prior to any production calculation, the convergence study with ecutwfc, k-points and ecutrho...
Camps's user avatar
  • 23.4k
3 votes
Accepted

Are the cell parameters found after doing a 'vc-relax' calculation the ones used to calculate the material properties?

The 'vc-relax' calculation aims to minimize the total energy of the system by adjusting the atomic positions and the cell shape, allowing the system to find a more stable configuration. The optimized ...
Pranav kumar's user avatar
  • 4,243
3 votes
Accepted

VASP structure relaxes to an incorrect ground state

This still looks okay to me, the bonds you see in VESTA are not real in the sense that they don't mean a covalent bond exists. There may be some weak bonding between layers (Are you certain this ...
Tristan Maxson's user avatar
2 votes

What's the appropriate method to create a supercell for Quantum ESPRESSO?

You can directly create a supercell using your input file of the optimized unit cell without optimizing the supercell. The optimized structure of the unit cell represents the most stable configuration ...
Marko_B's user avatar
  • 123
2 votes

Converging geometry of iron slab

You could try to relax a (much smaller) unit cell for iron, then after that is relaxed you can create and relax the slab with initial guess as the already pre-relaxed coordinates for the irons, which ...
Amir K's user avatar
  • 628
1 vote

VASP structure relaxes to an incorrect ground state

Two structures of POSCAR and CONTCAR you show are the same. When you open VESTA, you choose Edit --> Bond, then you edit a same Max. length. VESTA would show the same.
Binh Thien's user avatar
  • 2,095
1 vote

Cu FCC vc-relax method error

With the help of @Tyberius and @BrandonBocklund, I did the calculation of Cu in FCC lattice. Calculated lattice constant $a = 3.62613952 \, A^\circ$, where as experimental value is $a = 3.6149 \, A^\...
147875's user avatar
  • 663

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