| 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 |
|
|
