--- trunk/xDissertation/md.tex 2008/03/13 22:59:35 3369 +++ trunk/xDissertation/md.tex 2008/03/14 21:38:07 3370 @@ -140,18 +140,17 @@ $\sigma$ and $\epsilon$ parameters, Pechukas.\cite{Berne72} The potential is constructed in the familiar form of the Lennard-Jones function using orientation-dependent $\sigma$ and $\epsilon$ parameters, -\begin{equation} -\begin{split} +\begin{multline} V_{ij}({\mathbf{\hat u}_i}, {\mathbf{\hat u}_j}, {\mathbf{\hat -r}_{ij}}) = & 4\epsilon ({\mathbf{\hat u}_i}, {\mathbf{\hat u}_j}, +r}_{ij}}) = 4\epsilon ({\mathbf{\hat u}_i}, {\mathbf{\hat u}_j}, {\mathbf{\hat r}_{ij}})\left[ \left(\frac{\sigma_0}{r_{ij}-\sigma({\mathbf{\hat u}_i}, -{\mathbf{\hat u}_j}, {\mathbf{\hat r}_{ij}})+\sigma_0}\right)^{12} \right.\\ - &\left. -\left(\frac{\sigma_0}{r_{ij}-\sigma({\mathbf{\hat u}_i}, +{\mathbf{\hat u}_j}, {\mathbf{\hat r}_{ij}})+\sigma_0}\right)^{12} +\right. \\ +\left. - \left(\frac{\sigma_0}{r_{ij}-\sigma({\mathbf{\hat u}_i}, {\mathbf{\hat u}_j}, {\mathbf{\hat r}_{ij}})+\sigma_0}\right)^6\right] -\end{split} \label{mdeq:gb} -\end{equation} +\end{multline} The range $(\sigma({\bf \hat{u}}_{i},{\bf \hat{u}}_{j},{\bf \hat{r}}_{ij}))$, and strength $(\epsilon({\bf \hat{u}}_{i},{\bf @@ -172,19 +171,16 @@ calculate the range function, where $l$ and $d$ describe the length and width of each uniaxial ellipsoid. These shape anisotropy parameters can then be used to calculate the range function, -\begin{equation} -\begin{split} -& \sigma({\bf \hat{u}}_{i},{\bf \hat{u}}_{j},{\bf \hat{r}}_{ij}) = -\sigma_{0} \times \\ -& \left[ 1- \left\{ \frac{ \chi \alpha^2 ({\bf \hat{u}}_i \cdot {\bf +\begin{multline} +\sigma({\bf \hat{u}}_{i},{\bf \hat{u}}_{j},{\bf \hat{r}}_{ij}) = \\ +\sigma_0 \left[ 1 - \left\{ \frac{ \chi \alpha^2 ({\bf \hat{u}}_i \cdot {\bf \hat{r}}_{ij} ) + \chi \alpha^{-2} ({\bf \hat{u}}_j \cdot {\bf \hat{r}}_{ij} ) - 2 \chi^2 ({\bf \hat{u}}_i \cdot {\bf \hat{r}}_{ij} )({\bf \hat{u}}_j \cdot {\bf \hat{r}}_{ij} ) ({\bf \hat{u}}_i \cdot {\bf \hat{u}}_j)}{1 - \chi^2 \left({\bf \hat{u}}_i \cdot {\bf \hat{u}}_j\right)^2} \right\} -\right]^{-1/2} -\end{split} -\end{equation} +\right]^{-1/2} +\end{multline} Gay-Berne ellipsoids also have an energy scaling parameter, $\epsilon^s$, which describes the well depth for two identical @@ -211,18 +207,16 @@ The form of the strength function is somewhat complica \left[1-\chi^{2}({\bf \hat{u}}_{i}.{\bf \hat{u}}_{j})^{2}\right]^{-1/2} \end{eqnarray*} -\begin{equation*} -\begin{split} -& \epsilon_{2}({\bf \hat{u}}_{i},{\bf \hat{u}}_{j},{\bf \hat{r}}_{ij}) -= 1 - \\ -& \left\{ \frac{ \chi' \alpha'^2 ({\bf \hat{u}}_i \cdot {\bf +\begin{multline*} +\epsilon_{2}({\bf \hat{u}}_{i},{\bf \hat{u}}_{j},{\bf \hat{r}}_{ij}) += \\ +1 - \left\{ \frac{ \chi' \alpha'^2 ({\bf \hat{u}}_i \cdot {\bf \hat{r}}_{ij} ) + \chi' \alpha'^{-2} ({\bf \hat{u}}_j \cdot {\bf \hat{r}}_{ij} ) - 2 \chi'^2 ({\bf \hat{u}}_i \cdot {\bf \hat{r}}_{ij} )({\bf \hat{u}}_j \cdot {\bf \hat{r}}_{ij} ) ({\bf \hat{u}}_i \cdot {\bf \hat{u}}_j)}{1 - \chi'^2 \left({\bf \hat{u}}_i \cdot {\bf \hat{u}}_j\right)^2} \right\}, -\end{split} -\end{equation*} +\end{multline*} although many of the quantities and derivatives are identical with those obtained for the range parameter. Ref. \citen{Luckhurst90} has a particularly good explanation of the choice of the Gay-Berne @@ -702,7 +696,9 @@ D = \lim_{t \rightarrow \infty} \frac{1}{6 t} \langle We have computed translational diffusion constants for lipid molecules from the mean-square displacement, \begin{equation} -D = \lim_{t \rightarrow \infty} \frac{1}{6 t} \langle {|\left({\bf r}_{i}(t) - {\bf r}_{i}(0) \right)|}^2 \rangle, +D = \lim_{t \rightarrow \infty} \frac{1}{6 t} \langle {|\left({\bf +r}_{i}(t) - {\bf r}_{i}(0) \right)|}^2 \rangle, +\label{mdeq:msdisplacement} \end{equation} of the lipid bodies. Translational diffusion constants for the different head-to-tail size ratios (all at 300 K) are shown in table