Requesting spin density for a singlet open-shell calculation

[HenriqueCSJ]

I am trying to generate the spin density for a large open-shell singlet, but it seems that --uhf 0 can't generate a .cub file. Is there a way to force the spin density to be generated so one can study the spin topology in a magnetic system?

[kjelljorner]

Following the discussions in https://github.com/grimme-lab/xtb/issues/575, the concept of spin in xtb is somewhat vague and I'm not sure if it would even be possible to get a broken-symmetry spin.

I think for your purposes, the --fod would be a good option as outlined in the manual.

[haneug]

None of the GFNn-xTB methods has spin-dependent terms in their energy expression so there is no spin density available.

We are working on the incorporation of spin polarization into the GFN2-xTB Hamiltonian, but if broken-symmetry solutions will be available is to be seen.

Maybe the spin-flip concept can help you to investigate large singlet diradicals? (see https://pubs.acs.org/doi/10.1021/acs.jpca.9b03176)

[HenriqueCSJ]

Thank you so much for your kind answers and for the amazing software. It is impressive.