Chemistry Reference
In-Depth Information
Table 3 Total dipole moment (in [D]), individual components and enhancement (in %) for seven
amino acids from a simple point charge model with basis-set B3LYP/6-31 G(d,p)
Iteration
x
y
z
Dipole
Enhancement
0
0.3
0.4
12.4
12.4
-
1
0.7
0.0
14.4
14.4
16
2
0.7
0.0
14.7
14.7
19
3
0.7
0.0
14.8
14.8
19
0
2.5
0.9
11.0
11.3
-
1
3.5
0.5
14.2
14.6
29
2
3.6
0.3
15.0
15.4
36
3
3.7
0.2
15.2
15.7
39
0
10.5
5.0
4.5
12.4
-
1
13.1
6.1
4.6
15.2
23
2
13.7
6.2
4.6
15.7
27
3
13.8
6.3
4.6
15.9
28
0
5.4
11.8
4.8
13.8
-
1
7.1
14.9
5.7
17.4
26
7.5
15.5
2
5.9
18.2
32
3
7.6
15.7
5.9
18.4
33
0
7.7
4.1
6.5
10.9
-
1
9.8
4.8
8.5
13.8
27
2
10.2
4.9
9.2
14.6
34
3
10.3
4.9
9.2
14.7
35
0
4.2
3.8
10.0
11.5
-
1
4.8
4.9
12.1
13.9
21
2
4.9
5.2
12.6
14.5
26
3
4.9
5.2
12.7
14.6
27
0
14.3
0.3
6.6
15.8
-
1
19.9
1.0
10.0
22.3
41
2
20.3
1.1
10.4
22.8
44
3
10.5 22.9 45
Iteration 0 refers to the single molecule only, whereas iteration 1,2 and 3 refer to a calculation,
where the atomic point charges from the previous iteration surround the central molecule
20.4
1.1
when a wavefunction file exists. We therefore did not pursue the ONIOM procedure
to obtain dipole-moment enhancements in this study.
The main interest for performing single-point calculations in a cluster of point
charges was to get a simple estimate of dipole moments in a cluster, thereby
presenting a simple model of a crystal. Therefore, we also limited the size of the
basis set to 6-31 G(d,p) in the calculations reported in Table
3
. The DFT functional
used was B3LYP.
The result from these simple calculations is that substantial dipole-moment
enhancements can be observed for all seven amino acids studied. Hence, one could
expect them to occur frequently when a molecule becomes part of a crystal lattice.
However, these results depend on the approximation of a finite inhomogenous field
around the molecule and do not include any experimental information except for the
molecular geometry. This result will therefore be verified by experiment and by more
sophisticated methodology comparing experiment and theory in Sect.
5.1
.
