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<p>The iron oxyhydroxide lepidocrocite (γ-FeOOH) is an abundant mineral critical to a number of
chemical and technological applications. Of particular interest is the ground state and finite temperature magnetic order, and the subsequent impact this has upon crystal properties. The magnetic
properties, investigated in this work are governed primarily through superexchange interactions, and
have been calculated using density functional theory and cluster expansion methods. Quantification
of these exchange terms has facilitated the determination of the ground state magneto-crystalline
structure and subsequent calculation of its lattice constants, elastic moduli, cohesive enthalpy, and
electronic density of states. Further, using a collinear magnetic configuration model, the magnetic
heat capacity versus temperature has been studied and the N ́eel temperature obtained.
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Ground-state energies, densities and momentum distributions in closed-shell nuclei calculated within a cluster expansion approach and realistic interactions