With Firefly, the computed spin density is always rhoalpha-rhobeta density.
It is identically zero for singlets, but is a nontrivial function
for other multiplicities. For instance, it does not necessary have
the constant sign despite an excess of alpha electrons. The chemical
meaning of this is in the beta electron density becomes polarized by
the alpha electrons so that there are areas with excess of beta spins.
Hope this helps.
All the best,
On Tue Jul 22 '14 6:01pm, Pavlo Solntsev wrote
>Dear Alex and all forum users.
>I have calculated spin-density using CASSCF with the following line
> $eldens spind=.t. ieden=1 where=cube $end
> $cube $end
>I got my cube file, it looks good to me. But i realized it contains surface of two different signs: negative and positive. The positive sign in a spin density surface corresponding to a localization of electron(s). It makes total sense from the picture i got. But negative sign is not clear to me. Does it represent a hole? Does it have a chemical meaning? Do we need to worry about negative sign if we are interesting in location of the electron?
>I know, that spin density within UHF wavefunction is alpha-beta surface. But what about MCSCF wave function?
>Maybe someone from this forum has a reference related to the idea about spin density. It would be great.