[Pw_forum] Pseudo-potential testing

Gabriele Sclauzero sclauzer at sissa.it
Thu May 26 10:16:38 CEST 2011

Il giorno 26/mag/2011, alle ore 01.00, Tram Bui ha scritto:

> Dear Paul,
>        In the file that I have attached here (Paul's note on PP generation), under section 3.10: checking for transferability, you have mentioned about the:"The error on total energy differences
> between PP and AE results gives a feeling on how good the PP is." Do you mean the difference in AE and PP eigenvalues?

No, I think here Paolo "Paul" Giannozzi really meant what you understood first, but you didn't get it in the correct way.
You should really compare total energy differences, which means:
E_2(AE) - E_1(AE)    versus   E_2(PS) - E_1(PS)
where 1 and 2 label two different electronic configurations, and NOT
E_1(PS)  versus  E_1(AE)    
as you are probably trying to do.

> because I saw the Etot and Etotps are huge difference

This is often the case, given the high degree of freedom in the choice of PP parameters (especially for the local potential, I suppose).

> but their eigenvalue (e, Ry) are closed.

Indeed this is how it should be, since the modern PP are designed to reproduce the scattering properties of the AE atomic potential as best as possible.

> Dear QE users,
>      I'm trying to test the Cs' US PP with reference configuration of :[Xe] 6s1 5d0 6p0. To test the PP, I'm using these five configuration (just by guessing): 
>      configts(1)= '6s1 6p0 5d0'
>      configts(2)= '6s0.5 6p0.5 5d0'
>      configts(3)= '6s0.5 6p0 5d0.5'
>      configts(4)= '6s0 6p1 5d0'
>      configts(5)= '6s0 6p0 5d1'
> My questions are: 
>  - how to choose the configurations for PP testing based on the reference one? is there a strategy or some sort?

Use some reasonable configurations (remove or add one electron, or a fraction of it, move one or more electrons between different orbitals, ...).
The choice may also be driven by the class of materials that you are going to study (e.g. ionic crystals).

>  - how many configurations are enough for the test?

That's up to you... 5 look enough for me. Don't forget to do some testing with the solid state code (e.g. bond distance of dimers, lattice constant of simple solids...).



> Thank you very much,
> Tram Bui
> M.S. Materials Science & Engineering
> trambui at u.boisestate.edu
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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