Both the preference of germanium for D4R occupation as well as for the formation of germanium clusters -typically evaluated using a total count of Ge-O-Ge bonds -have already been discussed and tested in the literature. The germanium preference for D4R occupation was confirmed in a few periodic DFT investigations Fig. The global structure optimum for the UTL system with Si/Ge = 3.8 adopting a large simulation cell (Table )) -compare with Figure . The Ge content at this Si/Ge ratio allows for a complete filling of D4R units with germanium atoms, however, a partial spillover of Ge atoms towards the non-D4R T sites is observed. The structure is viewed approximately along the c-axis.