Chemistry Reference
In-Depth Information
The He-He optimized Pauli repulsion at medium range resulting from
Table 1.3 at R
1
S
g
10
3
E
h
, turns out to bewithin
¼
3a
0
,
D
E
ð
Þ¼
12
:
96
10
3
E
h
, obtained by Liu
andMcLean (1973) froman accurate SCFHartree-Fock calculation using
a4s3p2d1f basis of STOs on each centre. At R
1
S
þ
g
96%of the accurate result
D
E
ð
Þ¼
13
:
52
¼
4a
0
, the optimized result,
1
S
þ
g
10
3
E
h
, is still within 80% of the accurate value
given by the same authors,
D
E
ð
Þ¼
1
:
07
1
S
þ
10
3
E
h
. Apparently, our
results would be even better when compared with experiment
13
(Feltgen
et al., 1982), but in this case we must expect that our SCF values,
underestimating the interaction, compensate in part for the effect of the
attractive London forces not considered in the calculation.
These numerical results confirm the validity of our simple analysis
based on the exchange-overlap densities either for the chemical bond (H
2
)
or the Pauli repulsion (He-He). Even at the simple MO level, which we
know to behave correctly in the bond region (Magnasco, 2007, 2009a), a
model representing at its best such quantumdensities in terms of the single
one-electronH
D
E
ð
Þ¼
1
:
35
g
0 (Magnasco, 2004a)
is expected to give a qualitatively correct representation of the chemical
bond and its properties. This is what we want to present in the next
chapter.
€
uckel parameter
½ðba
S
Þ=ð
1
þ
S
Þ <
13
Our calculated value at R
¼
3
:
5a
0
would exceed by less than 2% the experimental value of
10
3
E
h
.
D
E
¼
3
:
74
