Rydberg states

Rydberg states can be seen as ionized molecules that are circled by a loosely bound electron. Because of their diffuse character, the central molecule appears almost like a point charge to the electron. And the states resemble the excited states of atomic hydrogen (the Rydberg series).

The example we are currently working on is morpholine. The highest occupied molecular orbital is a regular tight non-bonding orbital.
The LUMO (which also corresponds to the first excited state) is a diffuse s-type orbital.
The next three orbitals (yielding the next three states) are of p-type character. The first one is antisymmetric with respect to the molecular symmetry plane (i.e. it is of a" character).
And two more p-type orbitals follow in the other spatial directions.

It took some attempts to actually get nice pictures of the Rydberg orbitals. The problem is that they are very large and most programs in their default settings will not sample these areas. What I ended up doing is the following:

Use Turbomole to create .plt files but use a non-standard larger grid.

$pointval mo 23-30
grid1 vector 1 0 0 range -15,15 points 200
grid2 vector 0 1 0 range -15,15 points 200
grid3 vector 0 0 1 range -15,15 points 200

These files can be imported into VMD for plotting. For technical details and a script for automatizing it, see my earlier post.