Comment on “Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles”

International audienceSassi and Rosso 1 asserted to have rediscovered the akdalaite model of Michel and coworkers 2, 3 for the structure of ferrihydrite having a composition of Fe5O8H·nH2O (0 ≤ n ≤ 2) using ab initio calculations. Here, we show that the predicted polyhedral configuration and magnetic properties of the lowest enthalpy model correspond to those of hydromaghemite, not ferrihydrite. This is demonstrated by compiling results published in eleven uncited articles by seven independent research groups (Table 1). Taken together, the results in these articles validate the model structure of ferrihydrite obtained by X-ray diffraction 4 (Drits model) and do not support the model obtained from pair distribution function (PDF) analysis 2, 3 (Michel model). The results pertain to the chemical composition and structure of ferrihydrite, and are synthesized below in five statements that counter some of the hypotheses, statements, and interpretations in Sassi and Rosso