Abstract
Using density-functional theory, we investigate the stability, structural, magnetic, and electronic properties of the iron oxyhydroxide polymorphs [-, -, -, and ] under hydrostatic pressure. At ambient conditions goethite is the lowest energy phase, consistent with recent calorimetric measurements. Around 6–7 GPa we predict a transformation to the high-pressure phase. This structural transformation is followed by a high-spin to low-spin transition at 7.7 GPa, at much lower pressure than for other currently discussed iron-bearing minerals. While in the ground state the ions are coupled antiferromagnetically, at high pressures a strong competition to a ferromagnetic alignment is found in . Concerning the electronic properties, including an on-site Coulomb repulsion parameter ( method) improves the size of the zero-pressure band gaps substantially but shifts the spin transition to higher pressure (56.5 GPa). The predicted spin crossover is associated with a blueshift of 0.4 eV.
1 More- Received 23 July 2009
DOI:https://doi.org/10.1103/PhysRevB.80.205116
©2009 American Physical Society