I am not able to view Molecular Orbitals when I open a Cube file in Chem3D. The Molecular Orbitals option is greyed out.
If you are using Gaussian on a UNIX platform to create Cube files, you must make sure that you specify the Molecular Orbital in the property section when using the cubegen utility to create the Cube file. For example:
If you just leave the default and don't type "MO=something" you will only be able to display the Total Charge Density surface.