Table 1. Active Space Specifications for the S₀/S₁ MECP Optimizations^a.

Molecule	Structure	(ne,n0)	ns
ethylene	(a), (b), (c)	(2,2)	2
methaniminium	(d), (e), (f)	(2,2)	2
ketene	(g)	(2,3)	2
diazomethane	(h)	(2,3)	2
butadiene	(i)	(4,4)	3
”	(j), (k)	(4,4)	2
benzene	(l)	(6,6)	2
fulvene	(m)	(6,6)	2
azulene	(n)	(10,10)	2
s-indacene	(o)	(12,12)	2
PSB3	(p)	(6,6)	2
Me-PSB5	(q)	(10,10)	2
stilbene	(r)	(2,2)	3
GFP chromophore	(s)	(2,2)	3

^an_e, n_o, n_s: number of electrons, orbitals and states, respectively, in the SA-CASSCF procedure.