Chemistry Reference
In-Depth Information
r
ij
i
,
q
i
j
,
q
j
A
r
i
r
j
B
c.o.m.
c.o.m.
R
Figure 11.3 Interparticle distances in the intermolecular potential (c.o.m.: centre of
mass)
where q
i
and q
j
are the charges of particles i (belonging to A) and j
(belonging to B) interacting at the distance r
ij
.
11.3.1 Nonexpanded Energy Corrections up to Second
Order
If A
0
and B
0
are the unperturbed wavefunctions of molecules A (N
A
electrons) and B (N
B
electrons), and A
i
and B
j
a pair of excited pseudos-
tates describing single excitations on A and B, all fully antisymmetrized
within the space of A and B, we have to second order of RS perturbation
theory that
E
c
1
¼h
A
0
B
0
j
A
0
B
0
i¼
E
e
1
ð
11
:
34
Þ
is the semiclassical electrostatic energy arising in first order from the
interactions between undistorted A and B; that
¼
X
i
¼
X
i
2
2
jð
A
0
A
i
j
U
B
jh
A
i
B
0
j
A
0
B
0
ij
Þj
ind
;
A
E
ð
11
:
35
Þ
2
«
i
«
i
is the polarization (distortion) of A by the static field of B, described
by
U
B
¼h
B
0
j
B
0
i
ð
11
:
36
Þ
