Chemistry Reference
In-Depth Information
1
a
b
1.6
(10)_[cH]
(10)_[cH
2
]
(10)_[cH
3
]
(10)_[nH]
(10)_[nH
2
planar]
(10)_[nH
2
pyramidal]
(10)_[nH
3
]
(10)_[cooH]
(11-)_[cooH]
(10)_[oH]
(11-)_[oH]
(30)_[Nh
2
planar]
32+)_[Nh
2
planar]
(33-)_[Nh
2
pyramidal]
(30-)_ [Nh
2
pyramidal]
(30)_[Nh
3
]
(33+)_[Nh
3
]
(30)_[No
2
]
(32+)_[No
2
]
1.4
0.8
1.2
0.6
1
0.8
0.4
0.6
0.2
0.4
r
(angstrom)
0.2
r
(angstrom)
0
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
8
c
d
(40)_[Ch
3
]
(43+)_[Ch
3
]
(40)_[Co
2
]
(42+)_[Co
2
]
(44+)_[Co
2
]
(40)_[Cooh]
(41+)_[Cooh]
(42+)_[Cooh]
(43+)_[Cooh]
(44+)_[Cooh]
(40)_[Co]
(44+)_[Co]
(42-)-[C(sp
3
)h
2
]
(20)_[c/n-O-c]
(20)_[cO
2
]
(22+)_[cO
2
]
(22+)_[cOoh]
(22-)_[coOh]
(20)_[coOh]
(22-)_[Oh]
(20)_[Oh]
(22+)_[Oh]
(20)_[cO]
(22+)_[cO]
(20)_[nO
2
]
(22+)_[nO
2
]
0.8
7
6
0.6
5
4
0.4
3
2
0.2
1
r
(angstrom)
(angstrom)
0
0
-1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Fig. 6 Selected radial functions averaged over equivalent stockholder atoms: (a) H_R
1m
,
(b) N_R
3m
,(c) O_R
2m
,(d) C_R
4m
electronegativity of
X
. In other words,
H_R
10
[C-H]
is sharper than
H_R
10
[O-H]
.
The higher-order SPA-RDFs seem to be more sensitive to the chemical environ-
ment and thus are less transferable than the monopoles and dipoles.
The best agreement between various types of N-atoms is found for the octupole
functions (Fig.
6b
); the height of the maxima is very consistent, but their location is
slightly shifted closer to the N-nucleus in the nitro group. However, some higher-
order SPA-RDFs can be markedly different. For example, the
N_R
10
[NH
3
+
]
shows
a behavior that is opposite to that of
N_R
10
[NH
2
]
; the maxima and minima are
interchanged, while the locations of the extrema are preserved. The quadrupole
functions in the two types of amino groups (planar and pyramidal) are different not
only in terms of the height-maxima. For the nitro group, they depart considerably
from those in the two amino groups. The behavior of hexadecapole functions is
similar to that of quadrupoles.
All but three quadrupolar functions for the O-atoms (Fig.
6c
) show very similar
radial behavior and peak almost at the same location, but may differ in the height-
maximum:
O_R
20
[COO
]
,
O_R
20
[C
O]
and
O_R
20
[NO
2
]
. The main maximum of
the octupole SPA-RDFs is observed at the same distance from the nuclei
(
r
~ 0.5
˚
) for all types of O-atoms. Several of the octupole functions also show
a second maximum, sometimes separated by a node from the first one, while the
majority of the functions exhibit monotonic decay. A similar picture is observed for
haxadecapoles; most of these functions have only one maximum, change sign as
¼
