Equation with two sums but just one min and max

Question

I started with equations now and I got a problem with two sums in a row which should have the same symbol for minimum and the same symbol for maximum obove / under the sum symbols. The min and max should be in the middle of both sum symbols.

This is what I got right now:

\underbrace{\sum\sum^{N_{el}}_{I=1} \frac{Z_I}{r_{iI}}}_{\hat{V_{ee}}}

The code line is compiled ih the environment for equations. What I need is, is that the N_{el}is in the middle of both symbols and I=1 under both symbols. I used the amsmah package. But I could not find a way to work out the problem.

Answer 1

You make \sum\sum into a single mathop.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
[
\underbrace{\mathop{\sum\sum}^{N_{el}}{I=1} \frac{Z_I}{r{iI}}}{\hat{V{ee}}}
]
\end{document}

But the final result is far from being pretty. And why two summation signs? Also, please, fix the \hat{V_{ee}} horrible thing. It should likely be \hat{V}_{ee}.