Open NikoOinonen opened 5 months ago
My personal opinion is that it makes sense to apply this cutoff with a proper keyword and documentation later.
I would suggest the value for a cutoff to be as low as possible, but still bigger than density from VASP - as this is the "ground truth" testing code for the ppafm (not telling that the VASP or its density - e.g. soft PPs ... - just that we tune everything on it.
With this saying I would suggest, to update the code, once #275 is implemented. I think that this is also interesting for @mondracek
Hi, I was never using (or liking) FHI-aims to much. But I remember we had this problem with PPAFM from the start.
ad possible problems
@ProkopHapala
We should distinguish if we speak about Electrostacis (Hartree) or Pauli poentials.
Sorry I did not specify. I was only using the cutoff for the Pauli part. The electrostatics with aims does not pose any problem.
We agreed in the meeting that this should be implemented. I will try to get around to it some time soon.
I have been having some problems using electron densities from FHI-aims with the full-density-based model. The problem shows up in the simulated images as severe noise and artifacts in the mid to far range images.
Here is a random test molecule from our database which exhibits the issue: Far: Close:
The close range image is fine, but in the far-range image there is a lot of noise and a weird round artifact at the position of the Cl atom.
Since the problem only shows up at the far range, I first thought the issue might be something to do with the integration grid in aims, which gets more sparse further away from the atoms. However, after a quite a bit of testing, it looks like the issue actually stems from the core electrons. FHI-aims is an all-electron code so the density has sharp spikes at the positions of the atoms.
By simply applying a cutoff to the electron density, the issue seems to go away:
After trying a bunch of different cutoff values, it looks like somewhere around 100 the image becomes completely smooth for this particular case. Interestingly, going down even far as 1 with the cutoff still does not affect the close range image in any appreciable way. For reference, the original value at the position of the Cl atom is ~18000.
A line scan through the center of the Cl atoms:
It seems worth implementing this cutoff into ppafm in some way in order to make electron densities from aims also usable with the FDBM.
@ProkopHapala Do you foresee any problem with applying a cutoff in this way? It does get rid of some electrons, but then again, previously we have used the pseudo-potential densities that don't have the core electrons either.