--- trunk/mdRipple/mdripple.tex 2007/10/16 20:08:15 3263 +++ trunk/mdRipple/mdripple.tex 2007/10/18 21:07:03 3264 @@ -733,19 +733,44 @@ strength of the head group dipole moment strength of the head group dipole moment ($\mu$).\label{fig:phaseDiagram}} \end{figure} + +We have also computed orientational diffusion constants for the head +groups from the relaxation of the second-order Legendre polynomial +correlation function, +\begin{eqnarray} +C_{\ell}(t) & = & \langle P_{\ell}\left({\bf \mu}_{i}(t) \cdot {\bf +\mu}_{i}(0) \right) \rangle \\ \\ +& \approx & e^{-\ell(\ell + 1) \theta t}, +\end{eqnarray} +of the head group dipoles. In this last line, we have used a simple +``Debye''-like model for the relaxation of the correlation function, +specifically in the case when $\ell = 2$. The computed orientational +diffusion constants are given in table \ref{tab:relaxation}. The +notable feature we observe is that the orientational diffusion +constant for the head group exhibits an order of magnitude decrease +upon entering the rippled phase. Our orientational correlation times +are substantially in excess of those provided by... + + \begin{table*} \begin{minipage}{\linewidth} \begin{center} -\caption{} +\caption{Rotational diffusion constants for the head groups +($\theta_h$) and molecular bodies ($\theta_b$) as a function of the +head-to-body width ratio. The orientational mobility of the head +groups experiences an {\it order of magnitude decrease} upon entering +the rippled phase, which suggests that the rippling is tied to a +freezing out of head group orientational freedom. Uncertainties in +the last digit are indicated by the values in parentheses.} \begin{tabular}{lcc} \hline -$\sigma_h / d$ & $\theta_h (1/fs)$ & $\theta_b (1/fs)$ \\ +$\sigma_h / d$ & $\theta_h (\mu s^{-1})$ & $\theta_b (1/fs)$ \\ \hline -1.20 & $2.06 \times 10^{-10} \pm 1.27 \times 10^{-12}$ & $1.75 \times 10^{-11} \pm 4.83 \times 10^{-13}$ \\ -1.28 & $1.79 \times 10^{-10} \pm 2.27 \times 10^{-12}$ & $5.52 \times 10^{-11} \pm 2.20 \times 10^{-12}$ \\ -1.35 & $2.51 \times 10^{-11} \pm 1.19 \times 10^{-12}$ & $1.95 \times 10^{-10} \pm 2.86 \times 10^{-12}$ \\ -1.41 & $2.25 \times 10^{-11} \pm 1.05 \times 10^{-12}$ & $2.42 \times 10^{-11} \pm 3.19 \times 10^{-12}$ \\ +1.20 & $0.206(1) $ & $0.0175(5) $ \\ +1.28 & $0.179(2) $ & $0.055(2) $ \\ +1.35 & $0.025(1) $ & $0.195(3) $ \\ +1.41 & $0.023(1) $ & $0.024(3) $ \\ \end{tabular} \label{tab:relaxation} \end{center}