Table 2. ST Gaps (E_T – E_S) in eV and Errors with Respect to DEA-EOMCC[4p-2h]⁴³ (ref) Predictions^a.

system	CASSCF	AC1n	ACn	AC0	ftPBEb	RASPT2c	ref
1	0.44	0.18	0.13	0.00	0.11	0.19	0.18
2	–0.70	–0.71	–0.77	–0.86	–0.64	–0.65	–0.60
3	0.39	0.12	0.07	–0.08	0.03	0.11	0.12
4	0.41	0.17	0.12	–0.02	0.09	0.16	0.16
5	0.60	0.39	0.37	0.14	0.45	0.32	0.25
6	3.33	3.44	3.44	3.46	3.34	3.27	3.37
7	–0.92	–0.89	–0.90	–0.92	–0.66	–0.80	–0.80
ME	0.13	0.00	–0.03	–0.14	0.01	–0.01
MUE	0.20	0.06	0.08	0.16	0.09	0.04
MU%E	102.3	13.7	26.1	69.6	37.6	7.2
Std. Dev.	0.20	0.09	0.10	0.11	0.12	0.05

^aLabels: (1) C₄H₄, (2) C₅H₅⁺, (3) C₄H₃NH₂, (4) C₄H₃CHO, (5) C₄H₂NH₂(CHO), (6) C₄H₂-1,2-(CH₂)₂, and (7) C₄H₂-1,3-(CH₂)₂.

^bftPBE results taken from ref (52).

^cRASPT2 (valence-π, πCPO active space) results taken from ref (43).