TABLE VI.

Canonical CC2 excitation energies (in eV), the error of CC2 excitation energies computed with the present approach (in eV), and the percentage of VNOs and NAFs dropped using the default thresholds with the aug-cc-pVTZ basis set for bigger molecules.

Molecule	Number of atoms	Number of basis functions	State	Character	${\omega }_{\mathrm{CC2}}$	Error	Dropped VNOs	Dropped NAFs	Speedup
Hydrazone dye	21	828	S1	$\pi$ $\to {\pi }^{*}$	3.562	−0.012	58.1	80.7	14.1
			S2	CT	3.924	−0.016	59.0	80.9
			S3	$n,\sigma$ $\to {\pi }^{*}$	3.947	−0.015	58.9	80.8
			S4	$\pi$ $\to {\pi }^{*}$	4.180	−0.019	57.8	80.4
			S5	$n,\sigma$ $\to {\pi }^{*}$	4.527	−0.011	58.9	80.8
			S6	$n,\sigma$ $\to {\pi }^{*}$	4.543	−0.006	58.8	80.8
Diphenylamine	24	851	S1	$\pi$ $\to {\pi }^{*}$	4.334	−0.015	63.3	83.9	17.9
			S2	$\pi$ $\to {\pi }^{*}$	4.460	−0.024	63.3	83.7
			S3	Rydberg	4.627	0.014	63.4	83.8
			S4	Rydberg	4.994	0.048	63.3	83.9
			S5	Rydberg	5.084	0.037	63.2	84.0
			S6	Rydberg	5.229	0.026	63.2	83.9
Azobenzene	24	874	S1	$n,\sigma$ $\to {\pi }^{*}$	2.785	0.014	63.7	83.6	12.3
			S2	$\pi$ $\to {\pi }^{*}$	4.071	−0.018	62.6	83.3
			S3	$\pi$ $\to {\pi }^{*}$	4.427	−0.029	62.5	83.2
			S4	$\pi$ $\to {\pi }^{*}$	4.435	−0.029	62.6	83.3
			S5	$\pi$ $\to {\pi }^{*}$	5.155	−0.042	62.2	83.1
			S6	Rydberg	6.057	0.021	62.0	83.5
6,6′-difluoro-indigo	28	1150	S1	$\pi$ $\to {\pi }^{*}$	2.952	−0.016	58.3	80.9	12.8
			S2	$\pi$ $\to {\pi }^{*}$	3.436	−0.018	58.2	80.8
			S3	$\pi$ $\to {\pi }^{*}$	3.684	−0.027	58.2	80.9
			S4	$\pi$ $\to {\pi }^{*}$	3.725	−0.027	58.2	80.9
			S5	$\pi$ $\to {\pi }^{*}$	4.274	−0.023	58.1	80.9
			S6	$\pi$ $\to {\pi }^{*}$	4.775	−0.037	58.1	80.9
Bithiophene derivative	29	1135	S1	$\pi$ $\to {\pi }^{*}$	3.843	−0.026	59.4	82.3	17.8
			S2	$\pi$ $\to {\pi }^{*}$	4.631	−0.025	59.4	82.3
			S3	$\pi$ $\to {\pi }^{*}$	4.940	−0.034	59.2	82.2
			S4	$\pi$ $\to {\pi }^{*}$	5.446	0.002	59.2	82.4
			S5	Rydberg	5.538	0.009	59.1	82.3
			S6	$\pi$ $\to {\pi }^{*}$	5.602	−0.027	59.2	82.3
N-methyl-2,3-benzcarbaxole	31	1127	S1	$\pi$ $\to {\pi }^{*}$	3.332	−0.013	63.3	83.6	20.5
			S2	$\pi$ $\to {\pi }^{*}$	4.062	−0.021	63.4	83.6
			S3	Rydberg	4.468	0.020	63.1	83.8
			S4	$\pi$ $\to {\pi }^{*}$	4.510	−0.037	63.1	83.6
			S5	Rydberg	4.835	0.011	63.2	83.9
			S6	Rydberg	4.898	−0.017	63.2	83.9
Hydroxyflavone derivative	36	1311	S1	CT	3.382	−0.022	63.0	83.1	28.1
			S2	$\pi$ $\to {\pi }^{*}$	4.124	−0.030	63.0	83.1
			S3	$n,\sigma$ $\to {\pi }^{*}$	4.154	−0.020	63.0	83.2
			S4	$\pi$ $\to {\pi }^{*}$	4.227	−0.010	63.1	83.2
			S5	Rydberg	4.330	0.018	62.7	83.3
			S6	Rydberg	4.866	−0.037	62.6	83.3
Average						0.022a	61.1	82.6	17.6
Maximum						0.048b	63.7	84.0	28.1
Minimum						0.002c	57.8	80.4	12.3

^aMean absolute error.

^bMaximum absolute error.

^cMinimum absolute error.