[CP2K-user] [CP2K:21089] Re: Self-consistent Hirshfeld: How were ref atoms made, and can I extract them?

[Tian Lu]

Hello, 

I would like to mention that in the recent updates, Multiwfn 
(http://sobereva.com/multiwfn) has supported calculating Hirshfeld-I charge 
and MBIS charge (another method based on iterative atomic spaces) based on 
the .molden file or electron density .cube file exported by CP2K. Both 
isolated and periodic systems are supported. For the Hirshfeld-I 
calculation, radial electron density files for almost every element at 
every charged states have been provided in Multiwfn package 
("examples\atomrad\" subfolder) and can be directly used. I have a blog 
article to describe and illustrate how to perform the calculations using 
Multiwfn in combination with CP2K: http://sobereva.com/712 (currently 
written in Chinese, please use Google translator. English version may be 
available later). Please feel free to contact me if you have any problem.

Best regards,

Tian Lu

On Wednesday, January 29, 2025 at 8:05:13 AM UTC+2 Alexander Davis wrote:

> Hi,
>
> I have been calculating self-consistent Hirshfeld charges using my own 
> post-processing script, but I am thinking of switching to the CP2K 
> implementation. However, there are two questions I would need answered.
>
> One question is how it handles a well-known issue with this method, which 
> is that it obtains the shape function from the electron densities of free 
> ions, but sometimes these ions don't really exist. This is why my 
> implementation is unsatisfactory: I have references for N- and N2-, but the 
> electrons are not really attached, so the reference densities are too wide. 
> Every self-consistent Hirshfeld implementation as to handle this somehow, I 
> would like to know how CP2K handled it. The documentation says "This scales 
> only the full shape function, not the added charge as in the original 
> scheme", which is suggestive of a solution, but where can I read more about 
> it? If the details are in one of the publications, I missed it.
>
> My second question is whether I save the reference atoms as cube files, or 
> even better, the actual weight function used for integration (which is 
> a(r)/(a(r)+b(r)), where a and b are the reference atom densities). It's a 
> quirk of my application, I need precisely the weight function that was used 
> to calculate the charges.
>
> Thanks,
> Alex
>

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