where Occu Freq(class sites) is the Occupation Frequency (see Eq. 1) of Ge for a given type of T sites, N i is the total number of T sites of a given type in the simulation cell, and N is the total number of T sites in the cell. The Excess Ge-Count in D4R is calculated by multiplying the Excess Occupation by a factor n Ge /N D4R (see Figure as an example of use). The Excess Occupation measures the difference between the germanium occupation in a particular type of T sites (Eq. 1), e.g., D4Rs, and the germanium occupation which one would obtain assuming that the germanium is uniformly distributed across all the T-sites without any preference for different T-site types (the second term in Equation ).