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20 votes
Accepted

Linearized Augmented Plane Wave Method vs. Pseudopotential Methods

Disclaimer: I am a developer of the Fleur code. I hope that I don't put too much bias into this answer. At least I try to not do that... When you want to solve the Kohn-Sham equations you have the ...
Gregor Michalicek's user avatar
18 votes
Accepted

How to do periodic DFT calculations using Quantum ESPRESSO?

Unlike non-periodical DFT codes, Quantum ESPRESSO uses planewave basis sets and pseudopotentials. There are many ways of writing your input file, and it all depends on what information you have or ...
epalos's user avatar
  • 4,869
14 votes

How to do periodic DFT calculations using Quantum ESPRESSO?

You can start with following this Quantum Espresso Tutorial. The tutorial includes Hands On: scf, Energy bands, eqn of state, Geometry, cell optimization, Magnetism, DFT + U, CPMD, TDDFT, GW, Phonos, ...
Thomas's user avatar
  • 9,132
12 votes
Accepted

When are atomic-orbital-basis (rather than plane-wave) methods appropriate in periodic DFT?

The clearest example in my mind is if you want to understand the orbital-based contributions to some phenomena (e.g. bonding, a reaction energy), particularly if the periodic material being modeled is ...
Andrew Rosen's user avatar
  • 7,391
12 votes

How to do periodic DFT calculations using Quantum ESPRESSO?

Regarding input file format, check this website: https://www.materialscloud.org/work/tools/qeinputgenerator Format from this website will provide you a starting point. But please remind that the ...
exsonic01's user avatar
  • 873
10 votes

Are meta-GGA functionals SCAN (and its variants) ok to use in planewave DFT with the PBE pseudopotentials?

It is well known that using pseudopotentials generated with a functional which is inconsistent with the functional used in the plane-wave calculation can lead to serious problems, see here for example....
albapa's user avatar
  • 201
10 votes
Accepted

Energy cut-off test meaning in atomic-like basis functions' DFT

There is no energy cut off test for calculations that employ atomic basis sets, in general: the calculation is well-defined with just the atomic basis set. For comparison, the Gaussian-basis PySCF ...
Susi Lehtola's user avatar
  • 19.7k
9 votes
Accepted

Is basis set superposition error reduced when using the GAPW method?

Short answer: no. The idea of the GAPW method described in Theor. Chem. Acc. 103, 124 (1999) is simply to speed up the evaluation of the Coulomb and exchange-correlation contributions. Quoting from ...
Susi Lehtola's user avatar
  • 19.7k
5 votes

Simulation of charged species with plane-waves in Quantum Espresso

Personally, I prefer to use the second option. The full description of first option is: ...
Camps's user avatar
  • 23.4k
5 votes

Suggested cutoff for high level VASP calculations

Typically, the largest you would need for convergence, is ENCUT = 1.3 * ENMAX. This is the same as specifying as the ...
Xivi76's user avatar
  • 2,392
5 votes

When are atomic-orbital-basis (rather than plane-wave) methods appropriate in periodic DFT?

The question is related essentially to solve the Kohn-Sham equation with an atomic-like basis set. In fact, different implementations of DFT are distinguished mainly by their basis set and how they ...
Jack's user avatar
  • 15.2k
4 votes

Are meta-GGA functionals SCAN (and its variants) ok to use in planewave DFT with the PBE pseudopotentials?

New functionals often use PBE as a base. This is due to the benefit that everyone is using the same slightly incorrect psuedopotential, meaning it is reproducible. In VASP the psuedopotentials ...
Tristan Maxson's user avatar
4 votes
Accepted

Plane-wave basis expansion for periodic material modelling: cutoff energy inequality and number of atoms in the simulation

You’re quite right: as written, the equation is dimensionally inconsistent. There are actually a bunch of constants that make the units work out, but it is customary in matter modeling to define units ...
elutionary's user avatar
3 votes
Accepted

Acceptable core leakage

In the LAPW method, valence and core electrons are treated within the DFT self-consistency scheme according to the effective potential in each iteration. But nevertheless, they are separated. Only the ...
Gregor Michalicek's user avatar
3 votes
Accepted

Mixing pseudopotentials with gaussian and plane wave basis

This is the hybrid Gaussian and plane wave method described in Mol. Phys. 92, 477 (1997), in which you expand the orbitals $\psi_{i\sigma}$ in a Gaussian basis set, but compute the Coulomb interaction ...
Susi Lehtola's user avatar
  • 19.7k
3 votes

In plane-wave DFT, what needs to be converged and in what order?

The order of convergence tests you provided is a very good starting point which I believe will give very accurate numerical results in most cases. However, in my opinion and based on some prior ...
Jaafar Mehrez's user avatar
3 votes

Suggested cutoff for high level VASP calculations

I would go farther and ask, why is cutoff convergence unlike kpoint convergence? You can very easily do a convergence study based on energy cutoffs. Infact, this is often how ...
Tristan Maxson's user avatar
3 votes
Accepted

Kpt boundaries for cubic supercell

Ciao Marco! Once you make the supercell the reciprocal lattice vectors are divided by 2 (or whatever factor) automatically. The kptbounds are in reduced coordinates so no need to change the bound. ...
matthieu verstraete's user avatar
2 votes

MPI error in Quantum ESPRESSO during optimization of particularly large molecules

The comment by Pie86: "Try adding the option -ndiag 1 when running pw.x. It disables parallel diagonalization that raised similar problems in versions <= 7.1 (see gitlab.com/QEF/q-e/-/blob/...
2 votes
Accepted

In a plane-wave code, does the Fermi energy depend on the pseudopotentials used?

Your understanding is correct; you need to have a well-defined reference level for the Fermi level if you want to make comparisons between different systems (for example, comparing work functions of ...
Stephen's user avatar
  • 721
2 votes
Accepted

Plane wave basis functions

It does not matter: the coeficients are supposed to be complex, absorbing the phases.
Ryan's user avatar
  • 176
1 vote

In plane-wave DFT, what needs to be converged and in what order?

The order of convergence seems to be correct. As far as I have seen - In supercell calculations the convergence is not required. Only the K-mesh values are needed to be decreased from the unit cell. ...
epsilon02fft's user avatar
  • 1,522
1 vote

Compute solvation energies with (ESM) RISM-SCF

There are certain quantities that become poorly defined when you have a charged system. This could be what the author was referring to if you are studying the adsorption of ions or studying adsorption ...
Stephen's user avatar
  • 721

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