>Optional</span><span class="p">[</span><span class="nb">str</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">,</span>
                <span class="n">rmin</span><span class="p">:</span> <span class="nb">float</span> <span class="o">=</span> <span class="n">uc</span><span class="o">.</span><span class="n">set_in_units</span><span class="p">(</span><span class="mf">0.02</span><span class="p">,</span> <span class="s1">&#39;angstrom&#39;</span><span class="p">