Plotting Pictures of Molecular Orbitals

The following procedure plots the HOMO of benzene using Mopac.
A similar procedure can be used with Iconc and Firefly. 

First Optimise Geometry and then select Properties / Plot.MO from the Mopac Menu

You can select any orbital number. The default is the HOMO.
Click OK to select the HOMO and OK on the next dialog.
If you have MCE installed then the picture should look like.

If you do not have MCE installed then you will get simple contours which look like.

Some more details
The orbital choices on dialog11 are HOMO, LUMO or any M.O. by number. The M.O. no. of the HOMO is given on the Dialog to aid navigation to other M.O.s. The homo for benzene is M.O. no. 15 due to each C having 4 valence electrons (the 1s core is not included) and each H having 1 valence electron. The HOMO = (6 x 4 + 6 x 1)/2.

Using MCE with Moilin
MCE provides excellent quality mesh and surface plots. The program can be downloaded from
The programs authors Michal Husak, and Jan Rohlicek,
should be cited in any published use of the program.
If Moilin finds MCE installed it adjusts the defaults to best suit MCE.

Using the Benzene HOMO as an example. Click View on the Menu and select Level Control on the Primary and Secondary maps.
The negative values (Red) are controlled by the Primary Map and the Secondary Map controls the Blue positive values. The levels can be adjusted with the sliders or by entering a value. You should have the same absolute values in both maps.

If you select contour lines and apply you should get.

Some MCE controls - use the cursor keys to translate the molecule - use shift and a left click vertical drag to zoom the structure - use Preferences / Periodic Table (on the Menu) to change atom properties. Some bonds may not be drawn e.g. SOCl2 requires the S cov.tol. to be set to 0.2 to see the S=O bond.