\documentclass[12pt]{article}

\begin{document}

$$ 

E_{KE}  = \frac{\hbar^2 }{{m_{e} }}\sum\limits_i {\frac{3}{{2s_i^2 }}}

$$

\end{document}

\documentclass[12pt]{article}

\begin{document}

$$ 

E_{NN}  = \frac{1}{{4\pi \varepsilon _0 }}\sum\limits_{i < j} {\frac{{Z_i Z_j }}{{R_{ij} }}}

$$

\end{document}