In this manuscript Identifying Strong Covalent Interactions with Pauli Energy you are presenting 3D images of ELF values.
Is it possible to generate those wonderful images using multiwfn and gaussview...can you indicate me a path to follow?
In multiwfn, I understand that a cutting plane is used to generate 2D images. How can you know when metal-metal bond is present?
Please provide me with your references to know more about ELF and bonding.

You should first generate cube file of ELF file using main function 5 of Multiwfn. Then load the cube file into gview, then select "results"-"Surface/contours", then input a proper ELF isovalue in "Density" box, then select "Surface Actions"-"New Surface". Finally, click right mouse button on the graph, select "View"-"Display Format"-"Surface", choose "Transparent" in "Format" box. Now you should see a transparent isosurface enclosing your system.

Note that in the post-process menu of main function 5, you can also select option -1 to directly visualize the isosurface in Multiwfn.

There are many different ways supported by Multiwfn to study metal-metal bonds. For example, isosurface map of ELF/LOL/SCI, Mayer bond order, deformation density map, localized molecular orbitals and so on. Some discussions about Re-Re bond can be found in "Revealing Molecular Electronic Structure via Analysis of Valence Electron Density" (http://www.whxb.pku.edu.cn/EN/10.3866/PKU.WHXB201709252)

SCI can also be studied in Multiwfn. Firstly, change "iuserfunc" in settings.ini to 37 (if you don't know why do this, see Section 2.7 of the manual), then in the real function selection interface, the "100 User-defined function" will correspond to SCI.