Chemistry Reference
In-Depth Information
Table 19 Analysis of the ED at the BCPB of the terminal C-C bond. EDs are given in (e/
˚
3
),
Laplacians in (e/
˚
5
), and the contributions in percent
r BCP
ð
Þ
r
2
r
ð
BCP
Þ
Source function contributions to the ED at the BCP
Adjacent
a
One bond
b
Two bonds
b
Three or more bonds
b
(a)
Structures fully optimized
Ethane
1.86
22.40
79
21
-
-
Propane
1.63
14.29
78
20
3
-
Butane
1.64
14.38
78
19
2
1
Pentane
1.64
14.37
78
19
2
1
Hexane
1.64
14.37
78
19
2
1
14.38
Heptane
1.64
78
19
2
1
14.39
Octane
1.64
78
19
2
1
Nonane
1.64
14.39
78
19
2
1
Decane
1.64
14.39
79
21
0
0
(b)
Truncated systems at the geometry of decane, saturated with hydrogen
Ethane
1.64
14.41
81
19
-
-
Propane
1.64
14.35
78
20
2
-
Butane
1.64
14.41
78
19
2
1
Pentane
1.64
14.45
78
19
2
1
Hexane
1.64
14.45
78
19
2
1
Heptane
1.64
14.45
78
19
2
1
Octane
1.64
14.45
78
19
2
1
Nonane
1.64
14.45
78
19
2
1
Decane
14.45 78 19 2 1
(c)
Truncated systems at the geometry of decane, saturated with hydrogen, missing atoms replaced
by point charges
Ethane
1.64
1.64
14.44
81
19
-
-
Propane
1.64
14.33
78
20
2
-
Butane
1.64
14.40
78
19
2
1
Pentane
1.64
14.44
78
19
2
1
Hexane
1.64
14.45
78
19
2
1
Heptane
1.64
14.45
78
19
2
1
Octane
1.64
14.45
78
19
2
1
Nonane
1.64
14.45
78
19
2
1
Decane
1.64
14.45
78
19
2
1
a
Sum of contributions of the atoms which form the bond
b
Sum of contributions of the atoms being x covalent bonds away
a factor of two. This loss is compensated by an increased contribution arising from
the remaining carbon atom, so that the overall density remains constant. A similar
trend can be found for the terminal C-C bond (Table
19b
) for structures starting
from ethane.
As expected, the variations in the contributions are even smaller if the hydrogen-
linked atom method is used (Tables
18c
and
19c
). In summary, the investigations
showed that for the present kind of systems and chemical interactions (this conclu-
sion for instance would not necessarily hold for some transition metal complexes)
the source function can be used in QM/MM if the second neighbors are included in
the QM part. Qualitatively reasonable data are already obtained if only the next
neighbors are included in the QM part.
