@Brian Like everything, it depends on what properties you want. Anything that could resemble an excited-state property, you probably want an MCSCF reference. Geometries and vibrational frequencies are probably fine. I actually don't know how the CIS state energies look.
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@pentavalentcarbon I tried a quick ROCIS run on Cu(II) yesterday. The UHF/def2-TZVP wavefunction has Cu 4s as the beta LUMO, which is probably not right? It did show a nondegenerate ground state, for whatever it's worth. I didn't fiddle with the UHF to rotate down the nearest 3d orbital; could try it.
Of course, ORCA ROCIS choked when I tried it atop a ROHF wavefunction. ORCA kept insisting on using a "multiconfigurational ROHF wavefunction" (I think is the best term? Two orbitals had fractional occupancies.), and I'm guessing ROCIS didn't like that.
I agree with orthocresol. The question only requires that you must have knowledge of either Activities (at high-level) or Concentration (at elementary level). You must know have pre-requisite (the reason, I think, your question is an homework-one) about how we deal with concentration/activities i...
@orthocresol I had the same thought at first but then I realised that the chlorine atom is not directly attached to the carbon which is creating steric hinderance.
Has anyone tried drinking coffee out of their erlenmeyer flask mug? Because I have, and I think it made me realize why you're not supposed to drink out of lab equipment. It's really bad at retaining heat.