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Alex Granovsky
gran@classic.chem.msu.su

you are absolutely right. As triplet O₂ has exactly
half-filled high-spin open-shell, ROHF orbitals should work as well.
On the other side, for NO molecule they are not symmetric so one
may use ROHF orbitals of NO⁺ molecule instead.


Kind regards,
Alex

>>2. Initially, it is better start with RHF orbitals of closed-shell
>>axially-symmetric ion or neutral molecule. This will give you
>>starting orbitals of proper symmetry. E.g., RHF orbitals of singlet
>>N₂ in ground state are symmetric while RHF orbitals of singlet O₂ are not!

>Dear Alex. My problem is that in the case of O2 the ground state is triplet. That was the reason why I have started with ROHF orbitals. But probably it was my mistake, and the choise that you suggest is
>better.
>>For O₂, you would need RHF orbitals of O₂²⁺ system.