\begin{equation}
\mathbf{q}\cdot\mathbf{v}_{pq}^\mathrm{e} = \sum_{I}^{N_\mathrm{ts}}q_Iv_{pq,I}^\mathrm{e}

v_{pq,I}^\mathrm{e} = \left\langle \phi_p \left| \frac{-1}{|\mathbf{r} - \mathbf{s}_I|} \right| \phi_q \right\rangle
\end{equation}