Michael,
I develop the Orbital Viewer tool. Does it really say 0.0GB for both estimated peak memory usage and available memory? I've looked into it a bit, and it looks like the way I'm determining available memory is not the best. I'll release a patch for that soon. You might also have other applications open that are taking up memory.
I do not expect the estimated memory usage to be 0 GB. That's calculated directly from the grid size, number of threads, and number of atoms. If this does say 0.0 GB, I'd be interested in your orbital settings, basis set, and ORCA version.
As the message suggests, you can decrease the memory required by adjusting the resolution, padding, or number of threads on the 'orbital settings' tab of the Orbital Viewer tool. If you are able to load an orbital (with the resolution set to 0.75 A to be quick/safe), you can see how much extra padding you have by running the command `volume showOutlineBox true`. This will show the total volume where the orbital values were calculated, even though only the isosurface is shown. A smaller box (i.e. less padding) will require less memory at a given resolution.
The warning is there because exceeding the available memory could crash ChimeraX or force you to restart your computer. It's not meant to be a nuisance, so I'd like to make sure it's working properly.
Best,
Tony