n class="n">neighbors</span>
    <span class="n">species</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="nb">str</span><span class="p">,</span> <span class="n">struct</span><span class="o">.</span><span class="n">species</span><span class="p">))</span>
    <span class="c1"># in case of charged species</span>
    <span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">item</