Chemistry Reference
In-Depth Information
From these values, we obtain for the isotropic C
6
dispersion coefficient
for H
2
-H
2
C
6
¼
C
000
6
23E
h
a
0
¼
11
:
and for the first dipole anisotropy we have
C
020
020
0
6
C
6
¼
0
g
¼
:
098
which are respectively within 99.2% and
þ
2% of the accurate values
(C
6
¼
11
096) given by Magnasco and Ottonelli (1996a).
As a second example, illustrating a heterodimer calculation, consider
the C
6
dispersion coefficient of the H-H
2
system (atom-linear molecule
interaction):
:
32 and
g
6
¼
0
:
C
6
ðuÞ¼
C
6
½
1
þ g
6
P
2
ð
cos
uÞ
ð
11
:
52
Þ
where
3cos
2
u
1
2
P
2
ð
cos
uÞ¼
ð
11
:
53
Þ
is the Legendre polynomial of degree 2 (Chapter 3), C
6
is the isotropic
coefficient and
g
6
is the anisotropy coefficient. From Table 11.2:
C
020
6
A
B
A
þ
2B
C
6
¼
C
000
020
6
¼
2A
þ
4B
;
g
¼
C
6
¼
6
so that, using the four-term pseudospectrum for the H atom (Table 10.2)
and the one for the H
2
molecule (Table 11.3), we obtain A
¼
1
:
696 and
B
¼
1
269 and for the isotropic C
6
dispersion coefficient of the H-H
2
interaction we obtain
:
468E
h
a
0
C
6
¼
2
1
:
696
þ
4
1
:
269
¼
8
:
which is within 99.6% of the accurate value C
6
¼
8.502 (Magnasco,
Ottonelli, 1996b). The calculated value of
g
6
¼
0.101 exceeds the correct
