MultiWfn is a very useful program for wavefunction analysis. You can use a .wfn or .wfx wavefunction file for plotting any occupied orbital, but for a more accurate LUMO (and any LUMO +n) the formatted checkpoint file is needed. I use Gaussian 16 for its generation.
MultiWfn has a very complete manual that can be accessed here and a very informative YouTube channel with lots of video tutorials that can be accessed here.
I created this tutorial for my (and everyone’s) easy future reference because sometime’s it is kind of difficult to find the correct tutorial online or even browse through the manual!
Plot LUMO
- Open Multiwfn and drag and drop your .fchk file.
- Write 200 from the main functions menu: Other functions (part 2)
- Then choose the subfunction 3: *Generate cube file for multiple orbital wavefunctions * 4.Choose la for the alpha LUMO orbital.
- Choose the high quality grid by writing 3 (if your computer is slow, opt for a lower quality grid). A la.cub file is written.
- Copy the showcub.vmd file from the MultiWfn examples/scripts folder to your VMD folder.
- Open VMD and run the script by writing at VMD’s black console screen
source showcub.vmd - Then wirte cub la in your console. The alpha LUMO orbital will appear in your VMD window.
Refer to this post from sobereva for more details