ss="o">+</span> <span class="n">down_n</span><span class="p">)</span>
    <span class="n">Vxc</span> <span class="o">=</span> <span class="n">exchange_correlation_potential_operator</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">up_n</span> <span class="o">+</span> <span class="n">down_n</span><span class="p">)</span>
    <span class="n">H</span> <span class="o">=</span> <span class="n">K</span> <span class="o">+</span> <span class="n">Vext</span> <span class=