Dear users and developers.
I want to compute excitation energies for an organic chromophore in the presence of Rydberg orbitals.
The Rydberg basis is to be centred on the charge centroid of the molecule. So I must place there a dummy
(or a ghost atom?), and then assign to it a set of Rydberg basis functions.
My question is then: how can one specify a dummy centre in Psi4?
Marcin
You can add dummy atoms as described here: http://www.psicode.org/psi4manual/1.2/psithonmol.html#ghost-atoms
For your Rydberg basis, I would add a ghosted atom of a type that isn’t present in your molecule (I’ll use He) and then define a custom basis for that atom.
basis {
assign sto-3g
assign he my-made-up-basis
[ my-made-up-basis ]
cartesian
he 0
S 3 1.00
3.00 0.1
2.00 0.2
1.00 0.3
}
molecule {
0 1
h 0.0 0.0 0.0
h 0.0 0.0 1.0
gh(he) 0.0 0.0 2.0
}
energy(‘scf’)
I hope this helps.
Eugene
Thank you!
I have just managed to do it. 
Best regards!
Marcin