There are also other more specific aspects to consider regarding the preference of germanium for D4R occupation, namely the role of heterogeneity in D4R populations once there are more D4R units present in the simulation cell. These D4R units can be either crystallographically equivalent or inequivalent. The heterogeneity of D4R units in the former case has been probed recently for SOV and SOR 11 topologies (for a specific Si/Ge ratio and considering low tens of configurations). The results support the observation made herein about the large asymmetry in occupation of the individual D4R units in the simulation cell (Figure ). Hence, for the same Ge loading, a larger degree of Ge clustering can be achieved when the germanium atoms are spilled over in-between the germanium-rich D4Rs arranged along the layer than across the layer. Besides this distribution pattern, we may also distinguish some preference for the "spillover" germanium to spread along the specific directions (in the framework/adjacent sites) that are rich in S4R units, i.e., along the chain of S4R units in UOV and along the S4R-containing framework sites in the vicinity of the T2-site-edges of the two neighbouring D4Rs units in IWW (see SI Figures S20 S21) S22. For a topology with crystallographically inequivalent D4Rs units -UOV -we observe a strong dependence of the germanium occupation on the type of the D4R unit with the Ge occupation being the largest for "T3-T6" D4R and the smallest for "T14-T18" D4R unit. An explanation for this observation may be the larger lattice strain at the "T3-T6" D4R unit, with a few 5M-rings in the close vicinity (the vertex symbols of T3 and T6 sites are 4•5•4•6•4•10), to be contrasted with the more flexible environments of the "T14-T18" and "T17-T19" D4R units surrounded by 6M-or larger rings. We may hypothesize that such markedly different preferences for Ge occupation of the crystallographically inequivalent D4R units can be utilized to induce the hydrolytic instability into a specific crystallographic direction, i.e., the direction along which the (more) strained D4R units are arranged.