Table 2.

c‐P6⁴⁺ and c‐P6⁶⁺ DLPNO‐CC/Def‐SVP/C relative energy values with respect to the corresponding lowest value.^[a]

Species	Optimization	Geometry	ΔECCSD	ΔECCSD(T)
c‐P64+	B3LYP	min	0.0	0.0
	CAM‐B3LYP	min	−5.2	7.8
	M06‐2X	min	−1.8	5.5
c‐P66+	M06‐2X	min	0.0	0.0
	B3LYP	min	81.9	68.4
	CAM‐B3LYP	min	8.3	10.9
	CAM‐B3LYP	TS	32.4	25.0
	M06‐2X	TS	28.2	18.8

[a] All T₁ diagnostic ^[38] values are below 0.017. DFT calculations employed the 6‐31G* basis set. Energy in kcal mol⁻¹.