Quantifying changes in electron density observed across the Fe spin transition

Abstract:

Experimental charge density changes are compared to atomic orbital theory for d-electron spin collapse in high-pressure (Fe,Mg)O, characterized by the spin pairing of the two high energy lone-spin electrons in the Fe valence to a spin-paired state in lower-energy orbitals. Expected changes in bonding can be compared to ratios of local intensities to center-atom peak intensities. When normalizing to the oxygen site, we find general agreement for charge transfer around the cation site (5% local charge density changes) to expectation of 6% charge transfer for 53% Fe stoichiometry (two electrons in Fe divided by the total charge of the cation site). However, the change in charge density in the cation center is roughly twice as large (compared to oxygen) as expected from electron accounting, potentially related to expected electron donation from oxygen. Describing electron density distribution changes with compression allows for a comprehensive picture of high-pressure chemistry underpinning the theory in first-principles calculations, giving detailed insight into not only the confidence of measured properties but the electronic landscape leading to essential differences between deep-earth materials.