[Wien] Plane-wave cutoff in W2K

[Peter Blaha]

The energy cutoff for the planewave representation in the interstitial is $E_{max}^{wf}=19$ Ry for the wave functions and $E_{max}^{pot}=196$ Ry for
the potential."

A specification like this comes from the Pseudopotential community. We use different values:


The cutoff for the potential (and charge density) is specified in   case.in2(c). By default we use GMAX=12, while in this paper
GMAX=14 (E=k^2; 14^2=196 Ry) was used.

The cutoff for the wave functions is specified in case.in1(c), but as RMT(min) * Kmax
So the knowledge of "19 Ry" cutoff alone is not sufficient. You also need to know what their smallest RMT was.
Then RKmax = RMT(min) * sqrt(19).   Eg. an RMT=1.6 (for Oxygens) gives our default RKMax=7


> The authors specify their convergence parameters in the following way:
>
> "Inside the muffin tins wave functions are expanded in spherical harmonics up to $l_{max}^{wf}=10$ and nonspherical contributions to the electron density and potential up to
> $l_{max}^{pot}=6$ are used. The energy cutoff for the planewave representation in the interstitial is $E_{max}^{wf}=19$ Ry for the wave functions and $E_{max}^{pot}=196$ Ry for
> the potential."
>
> I would like to specify my parameters in the same way. For $l_{max}^{wf}$ and $l_{max}^{pot}$, these parameters are found in case.in <http://case.in>:
>
> 8.00       10    4 (R-MT*K-MAX; MAX L IN WF, V-NMT)
>
> and the last two would give me $l_{max}^{wf}$ and $l_{max}^{pot}$. However, I am in doubt on how to find the PW cutoff for the wavefunctions in the interstitials and for the
> potential (or how to determine these cutoffs, if they can't be readily found in the output files).
>
> For the wavefunctions, it is somewhat straightforward: kmax^2 gives the cutoff energy in Ry. I suppose I could just take the smallest cutoff (since there will be different kmax
> for the different elements) as a specification, or is the maximum/minimum value of kmax used for all elements, instead?
>
> For the expansion of potentials in plane waves, I'd suppose the energy cutoff would be simply gmax^2 (as specified in case.in2), but I'd like to confirm it, even under the risk of
> having made a stupid question :)
>
> Any help will be greatky appreciated.
>
> Thanks in advance,
>
> Marcos
>
> ---------------
> Marcos Veríssimo Alves
> Universidad de Cantabria, Spain
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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