Site assignment of atoms in crystals with multiply-occupied atomic sites can be determined uniquely using the bond valence method. We find that site assignments in which the weighted calculated valence sums are closest to the weighted formal valences yield excellent agreement with the chemical analysis. For any crystal, the method requires structure data and electron count for the sites in question; furthermore, if chemical analyses are available, these data may be incorporated into the method. The method minimizes the sum of squares of the difference between observed and calculated bond valence sums and observed and calculated electron occupancy by varying the fractional site occupancy for each potential substituent; terms for modeling chemical analyses can also be added, and the optimum solution is calculated by minimizing valence energy. Granted funds will be used to evaluate the model itself and test it extensively on mineral examples. Furthermore, because the student supported by the requested funds is returning to science after a disabling stroke, an important outcome of the research will be observations of enabling science to the disabled.
