You can contact me via E-mail.

Multiwfn supports lots of volumetric data formats, such as .cub, .vti, .dx, .grd, etc. The experimental electronic density must be recorded by one of them, so that Multiwfn can load and deal with it.

Best,

Tian

To compare the difference, you can for example, using Multiwfn to calculate grid data of electron density, and take its difference with electron density determined by X-ray. The resulting electron density difference map is useful in visually comparing the difference.

It is noteworthy that Multiwfn supports calculating electron density for periodic systems based on molden file produced by CP2K periodic DFT calculation.

I can provide more details if you need.

Best,

Tian

Xray is an amazing tool but sometimes due to resolution/sensitivity it does not always provide 100% answer.
I can get XYZs from Xray, but those do not tell us much about oxidation state or hydrogens attached. Often hydrogens are invisible, and in some cases the atom assignment is not clear.  For that reason I am not interested in XYZ geometry at this time, I would like to compare electron density somehow.

I am mainly interested in single molecule X-ray electron density and QTAIM analysis (with MultiWFN preferentially).
I was wondering if there is an accepted workflow to connect or compare experimental X-ray density data with those coming from DFT?

(incomplete) Some readings related to Hirshfeld atom refinement (HAR) and generalized atom refinement (GAR) which is capable of  localization of hydrogen atoms, bonding electrons and anisotropic refinement of hydrogen atoms:
      1. S. C. Capelli, H.-B. Burgi, B. Dittrich, S. Grabowsky, D. Jayatilaka, IUCrJ 2014, 1, 361-379.)
      2. M. L. Chodkiewicz, M. Woińska, K. Woźniak, IUCrJ 2020, 7, 1199-1215.
      3. M. Fugel, D. Jayatilaka, E. Hupf, J. Overgaard, V. R. Hathwar, P. Macchi, M. J. Turner, J. A. K. Howard, O. V. Dolomanov, H. Puschmann,  B. B. Iversen, H.-B. Burgi, S. Grabowsky, IUCrJ 2018, 5, 32-44.
      4. Tonto software package on github (https://github.com/dylan-jayatilaka/tonto) HARt performs Hirshfeld atom refinements

Thank you.
Theo

EDIT: My interest is mainly in open shell molecules, like radicals or transition metals