Lifting preprojective algebras to orders and categorifying partial flag varieties

We describe a categorification of the cluster algebra structure of multi-homogeneous coordinate rings of partial flag varieties of arbitrary Dynkin type using Cohen-Macaulay modules over orders. This completes the categorification of Geiss-Leclerc-Schr"oer by adding the missing coefficients. To achieve this, for an order $A$ and an idempotent $e\in A$, we introduce a subcategory ${\mathrm{CM}}_{e}A$ of $\mathrm{CM}A$ and study its properties. In particular, under some mild assumptions, we construct an equivalence of exact categories $(\operatorname{CM}\nolimits_e A)/[Ae] \cong \operatorname{Sub}\nolimits Q$foraninjective$B$-module$Q$where$B := A/(e)$. These results generalize work by Jensen-King-Su concerning the cluster algebra structure of the Grassmannian ${\mathrm{Gr}}_m({\mathbb{C}}^n)$.