# Tag Info

Accepted

### What is a Padé approximant?

To complement mykd's already excellent answer, I will just add that the approximant we all learn in school (the Taylor approximant) is nice to teach and easy to help students learn the concept of ...
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 ...
• 1,531

### What is a Padé approximant?

PADE refers to the mathematician Henri Padé, who developed the Padé approximation, which can approximate a function using rational polynomial functions. For ex:  \sin(x)\approx {\frac {(12671/...
• 2,342
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### Norm-Conserving or Ultrasoft, which pseudopotential to choose?

Three criteria to consider are Performance and size of basis set USPPs generally require a lower plane-wave cut-off and smaller basis, but a larger density grid. However performance may not be ...
• 571

### What is the difference between Ultrasoft, ONCV and PAW Pseudopotentials? Which is better for a spin-orbit coupled calculation?

Pseudopotentials (PPs) describe the effective interaction between the valence electrons and a nuclei screened by frozen core electrons. This approximation makes DFT calculations less computationally ...
• 418
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### When do relativistic effects need to be explicitly included?

When to include relativistic corrections or modeling of any kind in computational methods is a rather complex one. Full Dirac methods as you asked about (DHF) recapture two important factors, so ...
• 852

### What are the types of pseudopotentials?

Summary of the "milestone" pseudopotential (PP) papers Since it wasn't available anywhere & took me a few hours, it's an answer rather than question-edit: Local pseudo-potentials: 1935: ...
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### 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 ...
• 7,391
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### Understanding the GTH Pseudopotential

Great question, will allow me to advertize our newly-released DFT code :](https://github.com/JuliaMolSim/DFTK.jl/). The rloc parameter is the characteristic distance at which the pseudopotential acts....

### How to convert Unified Pseudopotential Format (UPF) into Ultrasoft Pseudopotential (USPP) format?

USPP is not a format of pseudopotential. It is a type of pseudopotential that enables you to work with lower cutoffs. On the other hand, upf is a popular file extension for pseudopotentials. If your ...
• 2,392
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### Why are Norm-conserving Pseudopotentials considered so important?

I think the best place to start is the original paper¹ proposing norm conserving pseudopotentials (NCPPs). It's very short and gives a nice explanation of why they were developed. I'll just give a ...
• 15.5k

### 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....
• 201

### For which elements should I include spin orbit coupling in Quantum ESPRESSO?

Spin-orbit coupling is related to relativity which is increasingly important for heavier elements. If you're aiming for ultra-high precision, as in this post on our site: How accurate are the most ...
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### For which elements should I include spin orbit coupling in Quantum ESPRESSO?

But in the case of the pseudo-potentials included, should I use fully relativistic pseudopotentials for all three elements? Yes, you should use the fully relativistic pseudopotentials if you are ...
• 15.2k

### What are the types of pseudopotentials?

To add to Nike's list, one should also differentiate between the energy consistent pseudopotentials used in quantum chemistry and the shape consistent pseudopotentials that dominate in the solid state ...
• 19.7k

### When should I include semi-core electrons in DFT calculations?

I am quoting from the book Materials Modelling Using Density Functional Theory: Properties and Predictions by Feliciano Giustino How do we decide which wavefunctions should be considered ‘core’ and ...
• 9,132
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### VASP GW PAW Pseudopotentials

A lot of it will be in the difference in cost. But as a rule of thumb, GW potentials are typically harder, and include more states (semicores). This need not always be the case, since if you look at ...
• 1,436
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### Error in nscf calculation while considering Spin Orbit Coupling in Quantum ESPRESSO

This error has been resolved now. Though I am not an expert but here are few thoughts. There may be several reasons for this error: This error might appear due to numerical instability from ...
• 2,611
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### Where can I find BLYP pseudopotentials?

Try searching for BLYP pseudopotentials here - http://pseudopotentials.quantum-espresso.org/legacy_tables/hartwigesen-goedecker-hutter-pp . One can generate BLYP and B3LYP pseudopotentials also.
• 1,522
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### How to choose hybrid pseudopotentials in Quantum ESPRESSO?

TLDR: enforce the hybrid functional using input_dft keyword. Check the exchange-correlation (XC) functional of your hybrid functional and use any pseudopotentials ...

### Norm-Conserving or Ultrasoft, which pseudopotential to choose?

The short answer is DEPENDS on your system and property of interest you are after (among other things). Anyway, I see the order of physical basis/complexity increasing as NC --> USPP --> PAW. But I ...
• 1,247
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### Can GW-BSE quasiparticle calculations only be run on norm-conserving pseudopotentials (NCPPs)? If so, why not?

The GPAW code can do GW/BSE and it uses purely PAW potentials. So it's absolutely possible to do GW/BSE with PAW sets. The involvement for the implementation, however, is another topic. From Kevin J. ...
• 1,436

### Are there properties that can only be calculated with a given set-up?

Only a partial answer: some setups are surely better suited than others for a given property. Some developers recognize this and thus do not bother implementing properties for which their setup will ...
• 1,697
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### Effective core potential (ECP) calculations

This is perfectly normal. In ab initio calculations, the energy zero point is usually chosen as the state where all explicitly described particles are infinitely far from each other and each ...
• 9,670

### Analytical expression for an atomic lattice "muffin-tin" potential for purposes of illustration and simple scattering calculations

The Augmented Plane Wave (APW) method, and by extension Linearly-Augmented Plane Wave method are both generalizations of the Muffin Tin Approximation. In both the APW and LAPW methods, the potential \$...
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### Quantum Espresso calculation for Deuterium

The main difference between deuterium and hydrogen is the mass, so you need to set the mass of the "hydrogen" so that it matches deuterium. I'm not a Quantum Espresso expert, but I think you ...
• 7,942
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### What is the meaning of energy-consistent and shape-consistent in the context of pseudopotentials?

This 2017 paper titled "Shape and Energy Consistent Pseudopotentials for Correlated Electron systems" defines energy-consistent psuedopotentials this way: "A combined reproduction of ...

### VASP Dielectric constants: What potential to use?

I don't think there is a consensus of norm conserving PP being more accurate. There are some references I am aware of which have calculated dielectric tensor using NC-PP, but without justification ...
• 1,247