You just need one wavefunction file. After loading it into Multiwfn, you can easily use main function 3 to plot ESP along a specific line. See Section 4.3 of Multiwfn manual for examples of using main function 3.

Hello,

I have a CI system for which I would like to obtain the electrostatic potential (ESP) along a line.
More precisely, I want to plot the ESP along a line approaching my system with a charge of -1.

Is there a way to do this using Multiwfn?

My guess is that I need to generate several .fchk files at various distances using Gaussian, but it's still unclear to me how to extract the ESP value, since Multiwfn typically plots the isosurface directly.

Thank you