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Questions tagged [cell-optimization]

For questions regarding optimizations of unit cell dimensions.

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13 votes
2 answers
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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
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13 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
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13 votes
1 answer
844 views

Structure relaxation of a thin film structure in VASP

I have some general questions about doing the structure relaxation of a thin film structure in VASP. I want to study the how the band structure evolves as we increase the number of layers of the ...
JensenPang's user avatar
  • 2,883
10 votes
2 answers
948 views

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

I'm a beginner when it comes to DFT and Quantum Espresso. Consider I have a lattice which has associated magnetic properties. So for geometric optimization should I take into account the magnetic ...
Anoop A Nair's user avatar
  • 4,496
10 votes
1 answer
1k views

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

Since I have started working on monolayers I was using the ISIF=3 tag for relaxation, this was after recompiling VASP with the modified "...
Chi Kou's user avatar
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9 votes
2 answers
3k views

Pressure applied DFT calculations in Quantum ESPRESSO

I am trying to perform the pressure-induced DFT calculations in Quantum ESPRESSO. For this, I have calculated the lattice constant of the cubic structure by vc-relax...
UJM's user avatar
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8 votes
3 answers
877 views

Cu FCC vc-relax method error

Reference: Density Functional Theory: A Practical Introduction, David Sholl, Janice A. Steckel, Chapter 2, Page No. 48 Section 2.2 The fcc Cu calculations in Fig. 2.3 used a cubic supercell with 4 Cu ...
147875's user avatar
  • 663
8 votes
1 answer
662 views

Why volume of unit cell is not the same as cubing the lattice constant?

I have a cubic-FCC with a=b=c and $\alpha$=$\beta$=$\gamma$=$90^o$. As far as I understand the volume of this cubic unit cell should be a cube of the lattice constant. But this not the case I am ...
UJM's user avatar
  • 2,611
7 votes
1 answer
168 views

Significant external pressure in non-SCF calculation results

I performed full structure optimisation (positions, cell volume and cell shape) using 15x15x3 k-mesh in VASP and safely assumed that the structure is reasonably relaxed as the external pressure found ~...
AbPhys's user avatar
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7 votes
1 answer
2k views

Meaning of lattice parameters in vc relax calculations

I am performing vc relax calculations to find the effect of pressure on the cell. Both tensile and compression pressure. But I am confused about the lattice ...
epsilon02fft's user avatar
  • 1,522
7 votes
1 answer
653 views

What parameters have to converge before doing a relax calculation?

I am a beginner of Quantum Espresso. I have taken 221 MoS2 Monolayer and done a relax calculation. In case of bulk system, or any doping in supercell, which is preferred: ...
Nithyadevi's user avatar
7 votes
1 answer
274 views

Smearing and charge balance for tungsten with interstitial oxygen in Quantum ESPRESSO

What smearing would be ideal for a bcc W with interstitial O atom. I am running 3x3x3 unit cells with one N interstitial. I am having convergence issues in relax ...
Dr.Viper's user avatar
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6 votes
1 answer
87 views

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

I am trying to perform DFT calculations for CsPbBr3 system on QE v7.2. To exploit symmetry i have given the space_group=221 and ...
Misbah 's user avatar
  • 343
6 votes
1 answer
181 views

How can I perform a cell shape relaxation in a specified direction using VASP?

According to VASP manual, the ISIF tag determines whether the stress tensor is calculated and which ionic degrees of freedom are varied. Suppose that I want to relax the cell shape in specific ...
Jaafar Mehrez's user avatar
6 votes
1 answer
675 views

Converging geometry of iron slab

I am a sort-of-beginner in Quantum Espresso. I do understand certain terminology in the INPUT file but I am faced with a dilemma. I have been trying to optimize $\ce{Fe}(110)$ system of 100 atoms ...
DevxAtom's user avatar
  • 149
5 votes
1 answer
130 views

What's the Difference between Lattice Statics and Lattice Dynamics?

For example, in something like the General Utility Lattice Program, you perform structural optimisation and then use phonons to calculate properties like elastic constants etc. The latter part seems ...
Connor's user avatar
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5 votes
1 answer
893 views

How to restart an interrupted Quantum ESPRESSO calculation?

I was doing a vc-relax calculation and after 1 day the calculation suddenly stopped. Is there a way to restart it from previous interrupted calculation of do I have to restart from the beginning?
Camilla's user avatar
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5 votes
1 answer
343 views

How to calculate lattice parameter?

After 'vc-relax' calculation I got the cell parameters in the picture bellow. I want to mention that my ibrav=1. I think the optimized lattice parameter in this case is A=11.44879234*1.006676454 .But ...
Camilla's user avatar
  • 2,159
5 votes
1 answer
232 views

How to get rotation matrix elements from root integer notation?

For example, I am reading a paper, where they put one layer on top of another, and in order to minimize the lattice mismatch, they transform unit cells of both layers. They report it in a root integer ...
Vladislav Gladkikh's user avatar
4 votes
2 answers
344 views

VASP structure relaxes to an incorrect ground state

I am using VASP to perform a structural relaxation of $\ce{CuNCN}$. I am using the PAW-PBE POTCAR files for the same and the KPOINTS have been generated using a script. The POSCAR file has been ...
Mriganka Parasar's user avatar
4 votes
1 answer
608 views

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

I created a CIF file using the experimental parameters of my material, then I used it to create my input file for the unit cell using Cif2Cell. After that, I ...
Camilla's user avatar
  • 2,159
4 votes
0 answers
32 views

Exicuting Quantum espresso vc-relax/relax calculation crashes with an error message saying more bands than PWs

I wanted to perform a vc-relax calculation for the FeS2 lattice with 12 atoms. The error message reads as follows for every tasks from 1 to 12. ...
AKSHAY PRAKASH HEGDE's user avatar
4 votes
0 answers
48 views

vc-relax calculation not converging with some pseudopotentials

I am new to Quantum ESPRESSO and it's my first calculations with $\mathrm{CsPbBr}_3$ perovskite structure. I am trying to perform vc-relax calculations. The ...
Misbah 's user avatar
  • 343
3 votes
1 answer
858 views

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

What is the procedure to do lattice optimization, encut optimization and kpoint optimization in VASP? Thank you in advance.
Maulesh VALA's user avatar
3 votes
0 answers
37 views

Relax calculation not converging

I am using a DFT+U+V approach and using a pseudohybrid density functional for extended Hubbard Coulomb interactions along with GBRV ultrasoft pseudopotentials (PBEsol). This enables me to open a gap ...
Austin's user avatar
  • 91
2 votes
1 answer
67 views

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

I created a CIF file using the experimental data from literature . After doing a 'vc-relax' calculation do I have to change the lattice parameter, CELL_PARAMETERS and ATOMIC_POSITIONS in my input file,...
Camilla's user avatar
  • 2,159
2 votes
0 answers
26 views

Strange change in total energy when lattice relaxing of EuTiO3 material and then atomic relaxing in a specific direction using Quantum Espresso

These days, I'm having a trouble in atomic relaxing of "EuTiO3" with tetragonal symmetry using Quantum espresso 7.1 for a period of more that a week. This material have a transverse optical ...
Y. S. Lym's user avatar
  • 143
2 votes
0 answers
99 views

Water simulation in ASE/LAMMPS

I want to simulate some water in MD with ASE and a LammpsLib calculator. I set up a minimal Lammps calculator and I try to calculate the energy per atom of an isolated molecule, and a 3x3x3 supercell. ...
Marco Di Gennaro's user avatar
2 votes
0 answers
84 views

Why the total energy calculated with GGA and metaGGA=SCAN are so different?

Why the total energy calculated with GGA and metaGGA=SCAN are so different? My INNCAR file is ...
babak ab's user avatar
2 votes
0 answers
56 views

Relaxation of a system with a different Forcefield

I have an amorphous silica surface system with 576 atoms which was generated using BKS forcefield. I would like to relax the system with Reaxff. To do that I use the fixes in lammps as, ...
Xdrake's user avatar
  • 541
2 votes
0 answers
119 views

Generating unit cell from an optimized molecule in Avogadro?

I am trying to generate the unit cell for a material from the optimized coordinates of a molecule. I am able to generate an orthorhombic unit cell from the coordinates using utilities in Avogadro. ...
Hemanth Haridas's user avatar
1 vote
0 answers
39 views

Relax calculation in Wien2k

Can someone help me with the steps to take to perform Relax calculation of a structure in WIEN2k? Then further what to keep in mind while performing strain calculation on the structure for the relax ...
epsilon02fft's user avatar
  • 1,522
1 vote
0 answers
42 views

Disappearing liaison when relaxing with Quantum ESPRESSO?

When I optimize the structure, the bonds between carbon atoms disappear, as shown in the figure. What could be the problem? my input file ...
SOELHADFI's user avatar
  • 433