This question about octaoxygen:
Why is octaoxygen diamagnetic?,
was asked in chemistry, but I really don't have an answer in terms of molecular orbitals. I think it could be a mixing of the O$_2$'s $\pi^*$ orbitals that have been bent inwards the monoclinic structure due to the high pressure of the $\varepsilon$-phase (about 10 GPa), thus greatly reducing sample volume, but I can't find a ressonant combination of 8 $\pi^*$ mixed orbitals that works.
I know that Gaussian can calculate molecular orbitals, but I don't have access to it.
My question is: is there any package out there, preferably free open-source software, which can calculate molecular orbitals of octaoxygen, which works for the gigapascal range (perhaps simulating cluster pressure with external electrostatic field)?
