Questions tagged [cell-optimization]

For questions regarding optimizations of unit cell dimensions.

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4 votes
2 answers
80 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 ...
6 votes
1 answer
138 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 ...
  • 119
7 votes
1 answer
354 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 ...
5 votes
1 answer
109 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 ...
  • 879
8 votes
3 answers
259 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 ...
  • 643
3 votes
1 answer
279 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.
7 votes
1 answer
237 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: ...
8 votes
1 answer
257 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 ...
  • 2,421
9 votes
2 answers
1k 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...
  • 2,421
8 votes
1 answer
371 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 "...
  • 5,531
12 votes
1 answer
396 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 ...
  • 2,733
7 votes
1 answer
176 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 ...
  • 457
12 votes
2 answers
687 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 ...
  • 2,421
10 votes
2 answers
534 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 ...
  • 4,278
11 votes
1 answer
3k 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....
  • 4,278