atomic_numbers</span> <span class="o">=</span> <span class="n">atomic_numbers</span><span class="o">.</span><span class="n">union</span><span class="p">(</span><span class="n">i_atomic_numbers</span><span class="p">)</span>
        <span class="n">symbols</span> <span class="o">=</span> <span class="n">symbols</span><span class="o">.</span><span class="n">union</span><span class="p">(</span><span class="n">i_symbols</span><span class="p">)</span>

        <span class="c1"># Gather maximum number of atoms</s