X-Git-Url: https://hackdaworld.org/gitweb/?p=lectures%2Flatex.git;a=blobdiff_plain;f=posic%2Fthesis%2Fd_tersoff.tex;h=b031be2f58ecd016152de51b4e26e136c23450aa;hp=84929638f3fd7f8a656fd7d51656dd426ef90f6e;hb=17d5c879c418790a154098e51c524eca183c4d98;hpb=dfeb4ccb085d878b5639dcaea7fcb7fcdc5248ad diff --git a/posic/thesis/d_tersoff.tex b/posic/thesis/d_tersoff.tex index 8492963..b031be2 100644 --- a/posic/thesis/d_tersoff.tex +++ b/posic/thesis/d_tersoff.tex @@ -3,7 +3,7 @@ \section{Form of the Tersoff potential and its derivative} -The Tersoff potential \cite{tersoff_m} is of the form +The Tersoff potential~\cite{tersoff_m} is of the form \begin{eqnarray} E & = & \sum_i E_i = \frac{1}{2} \sum_{i \ne j} V_{ij} \textrm{ ,} \\ V_{ij} & = & f_C(r_{ij}) [ f_R(r_{ij}) + b_{ij} f_A(r_{ij}) ] \textrm{ .} @@ -32,13 +32,13 @@ f_C(r_{ij}) = \left\{ 0, & r_{ij} > S_{ij} \end{array} \right. \end{equation} -with $\theta_{ijk}$ being the bond angle between bonds $ij$ and $ik$ as shown in Figure \ref{img:tersoff_angle}.\\ +with $\theta_{ijk}$ being the bond angle between bonds $ij$ and $ik$ as shown in Figure~\ref{img:tersoff_angle}.\\ \\ For a three body potential, if $V_{ij}$ is not equal to $V_{ji}$, the derivative is of the form \begin{equation} \nabla_{{\bf r}_i} E = \frac{1}{2} \big[ \sum_j ( \nabla_{{\bf r}_i} V_{ij} + \nabla_{{\bf r}_i} V_{ji} ) + \sum_k \sum_j \nabla_{{\bf r}_i} V_{jk} \big] \textrm{ .} \end{equation} -In the following all the necessary derivatives to calculate $\nabla_{{\bf r}_i} E$ are written down. +In the following, all the necessary derivatives to calculate $\nabla_{{\bf r}_i} E$ are written down. \section[Derivative of $V_{ij}$ with respect to ${r}_i$]{\boldmath Derivative of $V_{ij}$ with respect to ${\bf r}_i$} @@ -138,7 +138,7 @@ are calculated and added in subsequent loops. b_{ij} \nabla_{{\bf r}_j} f_A(r_{ij}) + f_A(r_{ij}) \nabla_{{\bf r}_j} b_{ij} \big] \end{eqnarray} -Using the equality $\nabla_{{\bf r}_i} r_{ij}=-\nabla_{{\bf r}_j} r_{ij}$ +Using the equality $\nabla_{{\bf r}_i} r_{ij}=-\nabla_{{\bf r}_j} r_{ij}$, the following relations are valid: \begin{eqnarray} \nabla_{{\bf r}_j} f_R(r_{ij}) &=& - \nabla_{{\bf r}_i} f_R(r_{ij}) \\ @@ -149,7 +149,7 @@ The pair contributions are, thus, easily obtained. The contribution of the bond order term is given by: \begin{eqnarray} \nabla_{{\bf r}_j}\cos\theta_{ijk} &=& - \nabla_{{\bf r}_j}\Big(\frac{{\bf r}_{ij}{\bf }r_{ik}}{r_{ij}r_{ik}}\Big) + \nabla_{{\bf r}_j}\Big(\frac{{\bf r}_{ij}{\bf r}_{ik}}{r_{ij}r_{ik}}\Big) \nonumber \\ &=& \frac{1}{r_{ij}r_{ik}}{\bf r}_{ik} - \frac{\cos\theta_{ijk}}{r_{ij}^2}{\bf r}_{ij} @@ -185,7 +185,7 @@ Concerning $b_{ij}$, in addition to the angular term, the derivative of the cut- \subsection{Code realization} -The implementation of the force evaluation shown in the following is applied to the potential designed by Erhard and Albe \cite{albe_sic_pot}. +The implementation of the force evaluation shown in the following is applied to the potential designed by Erhart and Albe~\cite{albe_sic_pot}. There are slight differences compared to the original potential by Tersoff: \begin{itemize} \item Difference in sign of the attractive part. @@ -220,7 +220,7 @@ LOOP i \{ \item \item LOOP k \{ \begin{itemize} - \item set $ik$-depending values + \item set $ik$-dependent values \item calculate: $r_{ik}$, $r_{ik}^2$ \item IF $r_{ik} > S_{ik}$ THEN CONTINUE \item calculate: $\theta_{ijk}$, $\cos(\theta_{ijk})$,