/em>, <em class="sig-param"><span class="n"><span class="pre">ucell</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><span class="pre">System</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">potential</span></span><span class="p"><span class="pre">:</span></span><span class="w"> </span><span class="n"><span class="pre">Potential</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">hkl</span></span><span cl