Table 5: Bond lengths 𝑅 𝑒 (Å) of the lowest states corresponding to the lowest two asymptotes.

Method 3 Π 𝑔 3 Σ + 𝑢 3 Π 𝑢 3 Σ + 𝑔 1 Π 𝑔 1 Σ + 𝑢 1 Π 𝑢 1 Σ + 𝑔

PQ2.3452.5324.2544.7652.3502.5964.7352.573
PT2.3472.5344.7954.792.3512.6024.7442.592
W91T2.3432.517diss4.5462.3472.621dis5.158
P0T2.3582.5175.0464.5172.3512.6312.7152.594
GP0T2.3562.522 diss5.8062.3452.7802.9294.755
CB3LT2.3432.489dissdiss2.3272.6132.6372.572
B3LT2.3712.566diss5.5252.3662.6552.8072.624
BLT2.3712.587diss4.8822.3762.648diss2.639
B86T2.3372.534diss4.5832.3412.6114.6475.370
LDAT2.2652.4542.7644.3642.2672.4852.7025.414
[17]a2.332.483.99diss2.302.642.402.74
[17]b2.352.504.11diss2.332.692.422.92
[87]c2.412.70dissdiss2.333.222.403.05
[19]d2.382.594.36diss2.382.642.65f2.65f
[88]d2.532.74diss2.512.972.643.07
[89]d2.562.70dissdiss2.482.922.64
[90]e2.3722.53
exp4.49g3.0g

TPresent work calculated with aug-cc-pVTZ and Qwith aug-cc-pVQZ basis set. P, W91, P0, GP0, B86, BL, B3L, and CB3L denote PBE, BPW91, PBE0, GRAC-PBE0, BP86, BLYP, B3LYP, and CAMB3LYP, respectively. aWith DK-CASPT2. bWith DK-MRACPF. cWith CI. dWith MRCI. eWith CCSD(T). fValue are ca. gFrom [85], for 3 Π 𝑢 [91] gives the value 3.30.