Given two solid bodies of masses $m_1$ and $m_2$ with invariable charge distributions $\rho_1(\mathbf{r_1})$ and $\rho_2(\mathbf{r_2})$ in them,* respectively, I would like to model the electrical interaction of the bodies using a user-specified electrical force law.
* $\mathbf{r_1}$ and $\mathbf{r_2}$ are measured with respect to a coordinate system fixed to body 1 and body 2, respectively.
What open source multiphysics software packages could I use to model the motion of these bodies?