+ - \frac{1}{3} <\sum_i {\bf r}_i \nabla_{{\bf r}_i} \foo> = -Nk_BT
+ \]
+ \begin{center}
+ mit
+ \end{center}
+ \[
+ - \nabla_{{\bf r}_i} \foo = {\bf f}_i^{tot} = {\bf f}_i^{ext} + {\bf f}_i^{int}
+ \]
+ \begin{center}
+ wobei
+ \end{center}
+ \[
+ \frac{1}{3} \sum_i {\bf r}_i {\bf f}_i^{ext}=-pV, \quad
+ \frac{1}{3} \sum_i {\bf r}_i {\bf f}_i^{int}=
+ - \frac{1}{3} \sum_i {\bf r}_i \nabla_{{\bf r}_i} \pot = \vir