the entire curve. The H core guess, however, does not remain in one state throughout
the curve. At 2.3 Å, a lower energy state is found, with an even lower energy state
appearing at 2.8 Å. While each state has
3 A 1 symmetry, the 2 > calc indicates
increasing spin contamination.
3.2 S-Block Diatomics
The s-block diatomics included in this study are LiF, NaCl, CaO, and MgO. The T 1 /
D 1 diagnostic values are listed in Table 4.
As expected, the multireference character increases as the bond breaks when the
internuclear separation increases. LiF and NaCl are well-behaved with both H core
Table 3 2
> calc − 2
> exact
at 0.1 Å increments along the
UHF curve for triplet O 2
O 2
H core guess
Hückel guess
r (Å)
< S
2
> calc − 2
> exact
2
> calc − 2
> exact
1.0
0.026
0.026
1.1
0.034
0.034
1.2
0.043
0.043
1.3
0.051
0.051
1.4
0.058
0.058
1.5
0.065
0.065
1.6
0.070
0.070
1.7
0.074
0.074
1.8
0.076
0.076
1.9
0.078
0.078
2.0
0.079
0.079
2.1
0.078
0.078
2.2
0.010
0.078
2.3
0.010
0.077
2.4
0.010
0.076
2.5
0.010
0.074
2.6
0.010
0.073
2.7
0.010
0.071
2.8
1.011
0.070
2.9
1.013
0.069
3.0
0.010
0.067
3.1
1.015
0.066
3.2
1.015
0.065
3.3
0.010
0.064
3.4
1.016
0.064
3.5
0.009
0.063
12
R. Weber et al.