n> <span class="ow">in</span> <span class="n">system_iterator</span><span class="p">:</span>
        <span class="n">n_atoms</span> <span class="o">=</span> <span class="nb">len</span><span class="p">(</span><span class="n">system</span><span class="p">)</span>

        <span class="c1"># Make ASE.Atoms into a System object</span>
        <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">system</span><span class="p">,</span> <span class="n">Atoms</span><span