[Wien] High accuracy calculations

[Stefaan Cottenier]

Let me give yet another different answer.

The initial question was about accuracy, while the parameters it referred to affect not accuracy yet only precision.

Precision = what was called ‘technical convergence’ by Laurence Marks.
Accuracy = difference between the DFT result and the experimental value (exclusively determined by the functional).

You can have a fully precise calculation with low accuracy. And even if you would have the exact functional (=fully accurate), but would be using a small basis set, your calculation would not be very precise.

The Delta test is about precision, not accuracy.

Hence, the better formulation of the initial question would have been ‘high-precision calculations’ (which would have made clear that it was not aiming at the functional).

Stefaan


Van: Wien [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] Namens Laurence Marks
Verzonden: vrijdag 13 april 2018 16:38
Aan: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
Onderwerp: Re: [Wien] High accuracy calculations

Let me give a different answer.

To perform a high accuracy calculation...use a high accuracy functional.

The technical convergence of, for instance, energy at a level of 0.01 eV/atom is easy, and the default parameters are close to good enough in most cases. (Phonons may require some care.)

The accuracy of some functionals is an order of magnitude larger than this, i.e. 0.1eV/atom or worse.
_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu<http://www.numis.northwestern.edu>

On Fri, Apr 13, 2018, 9:29 AM Gavin Abo <gsabo at crimson.ua.edu<mailto:gsabo at crimson.ua.edu>> wrote:
Regarding the SupplMat-WIEN2k.pdf at

https://urldefense.proofpoint.com/v2/url?u=https-3A__molmod.ugent.be_deltacodesdft&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=i1cULin_bn1tXhun33udTWyfJa5a0DXu_AhUGpJF-9E&s=d8WhT1rs3NF5IudCJnDFvFy87W1MFRyRUoXvlFeoo20&e=

I could be wrong, but it seems to be referring to lnsmax and lmax in
case.in1 and GMAX in case.in2 as seen in the WIEN2k usersguide [
https://urldefense.proofpoint.com/v2/url?u=http-3A__susi.theochem.tuwien.ac.at_reg-5Fuser_textbooks_usersguide.pdf&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=i1cULin_bn1tXhun33udTWyfJa5a0DXu_AhUGpJF-9E&s=9xncYwixf_vmWq4iLvqt1Ac_1AZDwTlEHL8FHaao_20&e= ].


On 4/13/2018 3:33 AM, Nils Longshower wrote:
> Hi!
>
> I have a question on some parameters to increase accuracy. In the
> supplementary materials for the delta tests, the following parameters
> are listed:
>
> * largest l-value of nonspherical Hamiltonian and overlap matrix
>
> * elements inside the spheres largest l-value in expansion of density
> and potential
>
> * largest vector in Fourier expansion of charge density
>
>
>
> Where do I set these parameters?
>
>
> Best,
> Nils
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