Table 3. Absolute Difference in Bond Lengths (Å) for Diatomic Molecules Using (AP)Δ-B3LYP and TD-DFT and (AP)Δ-HF and CIS.

sys.	Δ-B3LYP/TD-DFT	AP-Δ-B3LYP/TD-DFT	Δ-HF/CIS	AP-Δ-HF/CIS
BF	0.010	0.007	0.003	0.008
BH	0.023	0.014	0.011	0.004
CO	0.020	0.011	0.022	0.028
CuH	0.019	0.036	0.141	0.075
Li2	0.194	0.038	0.143	0.091
Mg2	0.041	0.075	0.225	0.086
N2	0.007	0.003	0.014	0.005
SiO	0.142	0.017	0.105	0.072
average difference	0.057	0.025	0.083	0.046