Chemistry Reference
In-Depth Information
they are paired. Using MD simulations, they explained this behavior as being
due to less hindered dynamics for the cation ring translational motion along
the direction of the carbon at the 3 position in the ring. This is the same direc-
tion that exhibits the lowest frequency contribution to vibrational density of
states obtained by Fourier transforming velocity-time correlation functions.
The top plot in Figure 17 contains the stress-stress autocorrelation func-
tion for [C
1
mim][Cl] at 425 K calculated by Bhargava and Balasubrama-
nian.
103
The rapid oscillations are due to high-frequency intramolecular
motions of the cation. The correlation function shows a rapid short-time decay
but a very slow long-time decay, as can be seen in the bottom graph in
1
0.5
0
-0.5
0
1
2
Time (ps)
3
4
(a)
0.06
0.04
0.02
0
0
100
200
Time (ps)
300
400
500
(b)
Figure 17
(a) Stress-stress correlation function for [C
1
mim][Cl] at 425K. (b) Estimated
viscosity from integrating the stress-stress correlation function. Notice the difference in
time scales. (From Ref. 103 and used with permission.)
