IQMOL Question: Is it possible to plot Frontier Density Surface?

I’ve seen that programs like WebMO and GaussView can plot what they call the frontier density surface. I looked at the IQMOL manual but couldn’t figure it out. Is this feature available in IQMOL?

If I understand what a frontier density surface is, then IQmol can plot these, but it’s a little fiddly and could be improved.

I could not find a defining equation on the web, but found the following description on the WebMO site:

Frontier density surfaces are computed from the magnitudes of the molecular orbitals available for attack by an electrophile, nucleophile, or radical.

Currently IQmol can plot the value an orbital on a density surface. First you need to generate the orbital volumetric data in a cube file and use this to colour the density isosurface (see the Visualizing Cube File Data section in the IQmol manual). This will plot the signed orbital value and to see just the magnitude you could change the colours so that both negative and positive values have the same colour.

One thing that is not clear from the above description is if the frontier surfaces are per orbital (which I have assumed), or if several frontier orbitals need to be summed over. If it is the latter, then some minor modifications to IQmol would be required.

Are you able to proved a more definitive reference or definition of a frontier density surface so I can make the modifications?

Thank you for the reply Dr. Gilbert. If I understand the papers below correctly (I understand organic chemistry more than quantum chemistry), it appears that some combination of the HOMO and LUMO are needed to calculate the frontier density surfaces. It also appears that a “dual-descriptor” (paper2) is a better method than the method that utilizes the Fukui functions (paper1).

There are other references related to the frontier density surfaces, here are two that I think are relevant ( I actually got these from the PSI4 online user manual section cubeprop(), and got to know about the “dual-descriptor” feature in PSI4):

  1. Christophe Morell, André Grand, and Alejandro Toro-Labbé J. Phys. Chem. A 109, 205 (2005)
  2. Jorge Ignacio Martínez-Araya J. Math. Chem. 53, 451 (2015)