Following #94 and similar bugs in the past, there was an idea to change nmo into an array, since it can change between SCF cycles as orbtials are dropped for various reasons. This issue is meant to collect our discussion on what to do with this.

Two aspects to consider:

• As Noel pointed out, changing the API would infer a major version change to cclib 2.x
• Changing nmo in this way suggests other attributes should also change that can behave similarly, including nbasis.