16

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 problem that the potential has singularities at the atomic nuclei. There are different ways to deal with this. On the one hand you can make the pseudopotential ...


15

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 what you want to learn. Here is the skeleton of your input file: =============================================================================== &CONTROL ...


12

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 more like a molecular solid where the chemical picture of orbitals is more intuitive than bands. There are several schemes out there that try to go from PAW to ...


12

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, Berry Phases, IR and Raman You can also follow Open online course on DFT, with simultaneous hands-on training on Quantum ESPRESSO. Available at any time for ...


11

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 result from this website IS NOT the ultimate solution and please do NOT regard the result from here as the "OK-button" solution. It seems that the example in your ...


9

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. It was also shown that for a potential-only meta-GGA (TB), the choice of pseudopotential makes a huge difference in the band gap, and in particular using PBE ...


8

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 program implements four ways to compute the Coulomb interactions in crystalline systems: Gaussian-basis density fitting mixed Gaussian-plane wave density fitting ...


8

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 the conclusions: Starting from the GPW approach we substituted the PW auxiliary basis for the electron density by an APW auxiliary basis which besides plane ...


5

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 orthogonalize themselves to the core levels. In particular, the choice of basis set forms the core of any electronic structure method. Dedepending on the choice ...


4

Typically, the largest you would need for convergence, is ENCUT = 1.3 * ENMAX. This is the same as specifying as the PREC = ACCURATE. Going beyond these typically only changes the energy of the system of very few meV.


4

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 cannot be generated by the user but codes like CASTEP and GPAW can generate them on the fly as needed. Using PBE as a base for SCAN is not ideal, but its consistent ...


2

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 ENMAX is determined in a code. Here is an example from the GPAW documentation of the convergence of the Ni PAW potential. As you can see, the error drops as the energy cutoff ...


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