220 |
|
external field applied in molecular dynamic runs. Once completed, the central nitrile bond frequency |
221 |
|
was calculated with a Morse fit. Using this fit and the solved energy |
222 |
|
levels for a Morse oscillator, the frequency was found. Each set of |
223 |
< |
frequencies were then convolved together with a guassian spread |
223 |
> |
frequencies were then convolved together with a lorezian lineshape |
224 |
|
function over each value. The width value used was 1.5. For the zero |
225 |
|
field spectrum, 67 frequencies were used and for the full field, 59 |
226 |
|
frequencies were used. |
274 |
|
of the liquid crystal. This change is consistent over the full 50 ns |
275 |
|
with no drop back into the isotropic phase. This change is clearly |
276 |
|
field induced and stable over a long period of simulation time. |
277 |
+ |
\begin{figure} |
278 |
+ |
\includegraphics[trim = 5mm 10mm 3mm 10mm, clip, width=3.25in]{P2} |
279 |
+ |
\caption{Ordering of each external field application over the course |
280 |
+ |
of 60 ns with a sampling every 100 ps. Each trajectory was started |
281 |
+ |
after equilibration with zero field applied.} |
282 |
+ |
\label{fig:orderParameter} |
283 |
+ |
\end{figure} |
284 |
|
|
285 |
|
Interestingly, the field that is needed to switch the phase of 5CB |
286 |
|
macroscopically is larger than 1 V. However, in this case, only a |
288 |
|
to the distance the field is being applied across. At such a small |
289 |
|
distance, the field is much larger than the macroscopic and thus |
290 |
|
easily induces a field dependent phase change. |
291 |
+ |
|
292 |
+ |
In the figure below, this phase change is represented nicely as |
293 |
+ |
ellipsoids that are created by the vector formed between the nitrogen |
294 |
+ |
of the nitrile group and the tail terminal carbon atom. These |
295 |
+ |
illistrate the change from isotropic phase to nematic change. Both the |
296 |
+ |
zero field and partial field images look mostly disordered. The |
297 |
+ |
partial field does look somewhat orded but without any overall order |
298 |
+ |
of the entire system. This is most likely a high point in the ordering |
299 |
+ |
for the trajectory. The full field image on the other hand looks much |
300 |
+ |
more ordered when compared to the two lower field simulations. |
301 |
+ |
\begin{figure} |
302 |
+ |
\includegraphics[width=7in]{Elip_3} |
303 |
+ |
\caption{Ellipsoid reprsentation of 5CB at three different |
304 |
+ |
field strengths, Zero Field (Left), Partial Field (Middle), and Full |
305 |
+ |
Field (Right) Each image was created by taking the final |
306 |
+ |
snapshot of each 60 ns run} |
307 |
+ |
\label{fig:Cigars} |
308 |
+ |
\end{figure} |
309 |
|
|
310 |
|
This change in phase was followed by two courses of further |
311 |
|
analysis. First was the replacement of the static nitrile bond with a |
325 |
|
With this important fact out of the way, differences between the two |
326 |
|
states are subtle but are very much present. The first and |
327 |
|
most notable is the apperance for a strong band near 2300 |
328 |
< |
cm\textsuperscript{-1}. |
304 |
< |
|
305 |
< |
After Gaussian calculations were performed on a set of snapshots, any |
328 |
> |
cm\textsuperscript{-1}. |
329 |
|
\begin{figure} |
307 |
– |
\includegraphics[trim = 5mm 10mm 3mm 10mm, clip, width=3.25in]{P2} |
308 |
– |
\caption{Ordering of each external field application over the course |
309 |
– |
of 60 ns with a sampling every 100 ps. Each trajectory was started |
310 |
– |
after equilibration with zero field applied.} |
311 |
– |
\label{fig:orderParameter} |
312 |
– |
\end{figure} |
313 |
– |
\begin{figure} |
330 |
|
\includegraphics[width=3.25in]{2Spectra} |
331 |
|
\caption{The classically calculated nitrile bond spetrum for no |
332 |
|
external field application (black) and full external field |
333 |
|
application (red)} |
334 |
|
\label{fig:twoSpectra} |
335 |
|
\end{figure} |
336 |
+ |
|
337 |
+ |
After Gaussian calculations were performed on a set of snapshots for |
338 |
+ |
the zero and full field simualtions, they were first investigated for |
339 |
+ |
any dependence on the local, with external field included, electric |
340 |
+ |
field. This was to see if a linear or non-linear relationship between |
341 |
+ |
the two could be utilized for generating spectra. This was done in |
342 |
+ |
part because of previous studies showing the frequency dependence of |
343 |
+ |
nitrile bonds to the electric fields generated locally between |
344 |
+ |
solvating water. It was seen that little to no dependence could be |
345 |
+ |
directly shown. This data is not shown. |
346 |
+ |
|
347 |
+ |
Since no explicit dependence was observed between the calculated |
348 |
+ |
frequency and the electric field, it was not a viable route for the |
349 |
+ |
calculation of a nitrile spectrum. Instead, the frequencies were taken |
350 |
+ |
and convolved together. These two spectra are seen below in Figure |
351 |
+ |
4. While the spectrum without a field is lower in intensity and is |
352 |
+ |
almost bimodel in distrobuiton, the external field spectrum is much |
353 |
+ |
more unimodel. This narrowing has the affect of increasing the |
354 |
+ |
intensity around 2226 cm\textsuperscript{-1} where the peak is |
355 |
+ |
centered. The external field also has fewer frequencies higher to the |
356 |
+ |
blue of the spectra. Unlike the the zero field, where some frequencies reach as high |
357 |
+ |
as 2280 cm\textsuperscript{-1}. |
358 |
|
\begin{figure} |
359 |
|
\includegraphics[width=3.25in]{Convolved} |
360 |
< |
\caption{Gaussian frequencies added together with gaussian } |
360 |
> |
\caption{Lorentzian convolved Gaussian frequencies of the zero field |
361 |
> |
system (black) and the full field system (red)} |
362 |
|
\label{fig:Con} |
363 |
|
\end{figure} |
325 |
– |
\begin{figure} |
326 |
– |
\includegraphics[width=7in]{Elip_3} |
327 |
– |
\caption{Ellipsoid reprsentation of 5CB at three different |
328 |
– |
field strengths, Zero Field (Left), Partial Field (Middle), and Full |
329 |
– |
Field (Right)} |
330 |
– |
\label{fig:Cigars} |
331 |
– |
\end{figure} |
332 |
– |
|
364 |
|
\section{Discussion} |
365 |
+ |
The absence of any electric field dependency of the freuquency with |
366 |
+ |
the Gaussian simulations is strange. A large base of research has been |
367 |
+ |
built upon the known tuning the nitrile bond as local field |
368 |
+ |
changes. This differences may be due to the absence of water. Many of |
369 |
+ |
the nitrile bond fitting maps are done in the presence of |
370 |
+ |
water. Liquid water is known to have a very high internal field which |
371 |
+ |
is much larger than the internal fields of neat 5CB. Even though the |
372 |
+ |
application of running Gaussian simulations followed by mappying to |
373 |
+ |
some classical parameter is easy and straight forward, this system |
374 |
+ |
illistrates how that 'go to' method can break down. |
375 |
|
|
376 |
+ |
While this makes the application of nitrile Stark effects in |
377 |
+ |
simulations of liquid water absent simulations harder, these data show |
378 |
+ |
that it is not a deal breaker. |
379 |
|
\section{Conclusions} |
380 |
|
\newpage |
381 |
|
|