mic_numbers</span> <span class="o">=</span> <span class="n">get_atomic_numbers</span><span class="p">(</span><span class="n">species</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_atomic_numbers</span> <span class="o">=</span> <span class="n">atomic_numbers</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_atomic_number_set</span> <span class="o">=</span> <span class="nb">set</span><span class="p">(</span><span cl