ns:</span>
<span class="sd">            If return_descriptor is True, returns a tuple, where the first item</span>
<span class="sd">            is the derivative array and the second is the descriptor array.</span>
<span class="sd">            Otherwise only returns the derivatives array. The derivatives array</span>
<span class="sd">            is a 4D numpy array. The dimensions are: [n_centers, n_atoms, 3,</span>
<span class="sd">            n_features]. The first dimension goes over the SOAP centers in 