%% 
%%  Ein Beispiel der DANTE-Edition
%%  Mathematiksatz mit LaTeX
%%  3. Auflage
%%  Beispiel 10-07-7 auf Seite 227.
%%  Copyright (C) 2018 Herbert Voss
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%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
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\documentclass[10pt]{screxa}
\pagestyle{empty}
\setlength\textwidth{170.40707pt}
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\begin{document}
\begin{align*}
\hat H\left(r,R\right)
  &= -\frac{1}{2}\sum\limits_{i=1}^N\nabla_i^2 -\frac{1}{2}\sum\limits_{I=1}^M
      \frac{1}{A_I}\nabla_I^2 +\sum\limits_{i=1}^N\sum\limits_{j>i}^N
      \frac{1}{\left|r_i-r_j\right|}\\
  &\mathrel{\phantom{=}}-\sum\limits_{i=1}^N \sum\limits_{I=1}^M
      \frac{Z_I}{\left|r_i-R_I \right|}+\sum\limits_{I=1}^M \sum\limits_{J>I}^M
      \frac{Z_I ZJ}{\left|R_I-R_J\right|}
\end{align*}
\end{document}