. 2016 Mar 10;144(10):104304. doi: 10.1063/1.4942019

TABLE XV.

Excitation energy differences [E(2¹A₁) − E(1¹A₁)], in mh.

		Active space of the reference wave function
		CAS(2,2)*	CAS(2,2)	CAS(6,4)*	CAS(6,4)	CAS(12,7)*^a	CAS(18,10)	CAS(12,9)*	CAS(18,12)
Geometry		Excluding 2s excitations	Including 2s excitations	Excluding 2s excitations	Including 2s excitations	Excluding 2s excitations	Including 2s excitations	Excluding 2s excitations	Including 2s excitations
OM	Ref.	194.38	194.38	96.21	96.21	98.57	99.56	156.95	152.51
	Ref. + SD	206.88	213.42	135.42	128.59	138.95	134.38	159.85	152.04
	Ref. + SDT	196.45	210.89	150.16		152.57		160.72
	Ref. + SDTQ^b	164.48	167.44	150.67		150.84
TS	Ref.	82.21	82.21	22.64	22.64	22.31	23.28	1.12	0.70
	Ref. + SD	29.82	36.72	13.83	17.19	9.66	12.16	1.50	1.43
	Ref. + SDT	17.08	26.56	5.27		2.02		1.63
	Ref. + SDTQ^b	2.42	6.56	2.82		0.51
		(3.34)^b
XM	Ref.	80.92	80.92	21.85	21.85	21.51	22.47	1.94	0.74
	Ref. + SD	28.68	35.53	12.86	16.25	8.69	11.20	1.86	1.58
	Ref. + SDT	16.25	25.60	4.32		2.23		2.06
	Ref. + SDTQ^b	2.39	9.89	2.86		−0.87
CI	Ref.	86.94	86.94	18.71	18.71	18.51	19.37	1.40	0.25
	Ref. + SD	30.30	36.70	12.13	15.02	8.27	10.73	1.17	0.89
	Ref. + SDT	17.48	26.54	4.29		1.66		1.37
	Ref. + SDTQ^b	1.02	8.66	−1.18		0.57
		(2.62)^b
RM	Ref.	402.51	402.51	294.39	294.39	296.40	295.95	286.51	289.42
	Ref. + SD	354.36	362.83	305.81	304.14	305.46	302.97	286.47	283.83
	Ref. + SDT	313.62	322.97	295.49		295.80		285.75
	Ref. + SDTQ^b	295.79	308.58	288.44		289.04

^{^a}

Energies for the CAS(12,7)* calculations were determined using the CASSCF(6,4) optimized orbitals (see the end of Section VI A).

^{^b}

The SDTQ values without parentheses were obtained using the CEEIS extrapolation for the CISDTQ increments. The values in parentheses for CAS(2,2)* were obtained by exact CISDTQ calculations.