TABLE IV.

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 small molecules.

Molecule	Character	State	${\omega }_{\mathrm{CC2}}$	Error	Dropped VNOs	Dropped NAFs
Acetamide	$n\to {\pi }^{*}$	S1	5.605	−0.033	63.6	82.9
	Rydberg	S2	5.917	−0.031	61.5	82.7
	Rydberg	S3	6.456	0.034	61.8	82.6
Acetone	$n\to {\pi }^{*}$	S1	4.454	−0.001	65.0	83.4
	$\sigma \to {\pi }^{*}$	S13	9.110	−0.007	64.7	83.6
	$\pi \to {\pi }^{*}$	S14	9.212	0.052	62.4	83.4
Benzene	$\pi \to {\pi }^{*}$	S1	5.220	−0.017	63.4	84.0
	$\pi \to {\pi }^{*}$	S3	6.452	0.035	63.9	84.5
Butadiene	$\pi \to {\pi }^{*}$	S1	6.134	−0.009	63.2	83.7
	$\pi \to {\pi }^{*}$	S5	7.064	−0.004	63.8	84.6
Formaldehyde	$n\to {\pi }^{*}$	S1	3.996	0.041	58.8	80.3
	$\sigma \to {\pi }^{*}$	S6	9.191	0.010	59.2	80.6
	$\pi \to {\pi }^{*}$	S13	10.698	0.022	57.7	81.2
Formamide	Rydberg	S3	6.697	0.034	58.5	80.9
CTa at 5Å	CT	S1	6.728	0.013	56.1	79.5
CTa at 10Å	CT	S1	6.740	0.020	56.8	79.7
Average				0.023b	61.3	82.3
Maximum				0.052c	65.0	84.6
Minimum				0.001d	56.1	79.5

^aEthylene-tetrafluoroethylene model.

^bMean absolute error.

^cMaximum absolute error.

^dMinimum absolute error.