reference atomic CDDs. Fortunately, this problem can be resolved by using the iterative Hirshfeld-I scheme.[@BultinckP:2007FaradDisc_HirRef; @BultinckP:2007JCP_HirRef] For each iteration $i$, the obtained $\rho^{AIM}_{A}(\mathbf{r})$ are used to calculate the population $n^{i}_{A}$ of each atom $A$. The (spherically symmetric) CDD $\rho^{i}_{A}(n_{A}^{i},\mathbf{r})$ of a free atom $A$ with population $n^{i}_{A}$ is then used as atomic CDD in . For each iteration the new promolecular density $\rho^{i}_{promol}(\mathbf{r})$ is obtained by summing the density distributions $\rho^{i}_{A}(n_{A}^{i},\mathbf{r})$ for all atoms of the molecule. This setup is independent of the initial choice of atomic CDDs and the convergence of the iterative scheme is determined by the convergence of the populations of the AIM.[@BultinckPAyersPWFiasS:2007ChemPhysLett; @GhillemijnDBultinckP:2011JCompChem] Note that the first step in this scheme usually corresponds to the standard Hirshfeld method with $n_{X}^{\circ}=Z_{X}$. At this point it is important to note that the CDDs $\rho^{AIM}_{A}(\mathbf{r})$ and $\rho_{A}^{i}(n_{A}^{i},\mathbf{r})$ will generally be different, despite having the same population. $\rho_{A}^{i}(n_{A}^{i},\mathbf{r})$ is constructed as a spherically symmetric CDD, whereas $\rho_{A}^{AIM}(\mathbf{r})$ is a weighted part of the molecular CDD. The resulting CDD will generally be not spherically symmetric but show protrusions along the directions bonds are formed.\
The extension of the Hirshfeld and Hirshfeld-I methods from molecules to bulk and other periodic materials is 