Plot the PAW densities.

        Args:
            ax: matplotlib :class:`Axes` or None if a new figure should be created.

        Returns:
            `matplotlib` figure

def plot_densities(self, ax=None, **kwargs):
        """
        Plot the PAW densities.

        Args:
            ax: matplotlib :class:`Axes` or None if a new figure should be created.

        Returns:
            `matplotlib` figure
        """
        ax, fig, plt = get_ax_fig_plt(ax)

        ax.grid(True)
        ax.set_xlabel('r [Bohr]')
        #ax.set_ylabel('density')

        for i, den_name in enumerate(["ae_core_density", "pseudo_core_density"]):
            rden = getattr(self, den_name)
            label = "$n_c$" if i == 1 else r"$\tilde{n}_c$"
            ax.plot(rden.mesh, rden.mesh * rden.values, label=label, lw=2)

        ax.legend(loc="best")

        return fig