In addition, if you prefer to manually generate the wavefunction files for N, N-1 and N+1 states and generate Fukui functions using the way described in Section 4.5.4 of Multiwfn manual, you can also use many codes other than Gaussian to generate them, such as ORCA, GAMESS-US, NWChem, MRCC, Dalton and so on, all of them are freely available. See beginning part of Chapter 4 on how to do.

However, as Gaussian is a commercial software and I currently do not have access to a licensed version, I was wondering if you could kindly recommend an alternative method or tool to compute Fukui functions.

Any advice or suggestions would be greatly appreciated.

Main function 0 of Multiwfn is able to directly plot isosurface map of MOs, see Section 4.0 of Multiwfn manual for example.

To generate and plot Fukui functions in Multiwfn, please follow the example in Section 4.22.1 of Multiwfn manual.

I have a question regarding visualization of molecular orbitals and reactivity indices using Multiwfn.

Specifically, I would like to know whether it is possible to generate images of HOMO/LUMO and Fukui functions directly in Multiwfn, or if this type of visualization can only be done using external programs such as VMD or GaussView.

If Multiwfn itself can produce such images, could you please advise which section of the manual I should refer to for detailed instructions?

Thank you very much for your guidance.

Sincerely,
YJ