[CP2K-user] [CP2K:15575] GAPW: How does r_loc affect energies?

[Krack Matthias (PSI)]

Hello Hayden

r_loc defines the exponent \alpha_C of the core charge distribution. Check section 2.3 of this reference<https://doi.org/10.1039/B001167N> for further details. While this parameter is part of the parameter set of the GTH pseudopotentials (local part), it can be in principle arbitrarily chosen for all-electron calculations, but for reasons of computational efficiency and accuracy, r_loc should not be too small or too large. 0.5 turned out to be a reasonable choice, which should also work for At.
The atomic regions for the hard part of GAPW are defined by the HARD_EXP_RADIUS<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND.html#HARD_EXP_RADIUS> keyword key.

HTH

Matthias

Von: cp... at googlegroups.com <cp... at googlegroups.com> Im Auftrag von Hayden Scheiber
Gesendet: Dienstag, 15. Juni 2021 22:36
An: cp2k <cp... at googlegroups.com>
Betreff: [CP2K:15575] GAPW: How does r_loc affect energies?

Hello,

I'm attempting a series of all-electron DFT calculations involving the At- ion, but astatine is not defined in the ALL_POTENTIALS file. I added in my own astatine section into my local ALL_POTENTIALS file as follows:

At ALLELECTRON ALL
   12   29   30    14
     r_loc    0
#

I don't know what choice of r_loc to use (e.g. 0.5 is used for iodine). I can't find any documentation on how r_loc values are chosen. I believe that r_loc defines the border between the hard (local) and soft (interstitial) parts of the GAPW calculation. Is this correct? I attempted a few test calculations with varying values of r_loc on a non-periodic At atom, and the resulting total energy varies a lot (10s of Hartrees). Why does the energy vary so much with r_loc? How should I select my value of r_loc?

Attached is the CP2K input I'm using.


Thanks,

Hayden Scheiber


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