W. M. Temmerman

Understanding the valency of rare earths from first-principles theory

The rare-earth metals have high magnetic moments and a diverse range of magnetic structures. Their magnetic properties are determined by the occupancy of the strongly localized 4f electronic shells, while the outer s–d electrons determine the bonding and other electronic properties. Most of the rare-earth atoms are divalent, but generally become trivalent in the metallic state. In some materials, the energy difference between these valence states is small and, by changing some external parameter (such as pressure), a transition from one to the other occurs. But the mechanism underlying this transition and the reason for the differing valence states are not well understood. Here we report first-principles electronic-structure calculations that enable us to determine both the valency and the lattice size as a function of atomic number, and hence understand the valence transitions. We find that there are two types of f electrons: localized core-like f electrons that determine the valency, and delocalized band-like f electrons that are formed through hybridization with the s–d bands and which participate in bonding. The latter are found only in the trivalent systems; if their number exceeds a certain threshold, it becomes energetically favourable for these electrons to localize, causing a transition to a divalent ground state.

Electronic structures of normal and inverse spinel ferrites from first principles

We apply the self-interaction corrected local spin density approximation to study the electronic structure and magnetic properties of the spinel ferrites

Half-metallic to insulating behavior of rare-earth nitrides

\mathrm{Mn}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}

First principles study of rare-earth oxides

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Electronic structure and ionicity of actinide oxides from first principles

{\mathrm{Fe}}_{3}{\mathrm{O}}_{4}

The electronic structure of europium chalcogenides and pnictides

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Structural phase transitions and fundamental band gaps of MgxZn1-xO alloys from first principles

\mathrm{Co}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}

Electronic structure of half-metallic double perovskites

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Exchange coupling in transition metal monoxides: Electronic structure calculations

\mathrm{Ni}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}

Pressure‐Induced Valence Transitions in Rare Earth Chalcogenides and Pnictides

. We concentrate on establishing the nominal valence of the transition metal elements and the ground state structure, based on the study of various valence scenarios for both the inverse and normal spinel structures for all the systems. For both structures we find all the studied compounds to be insulating, but with smaller gaps in the normal spinel scenario. On the contrary, the calculated spin magnetic moments and the exchange splitting of the conduction bands are seen to increase dramatically when moving from the inverse spinel structure to the normal spinel kind. We find substantial orbital moments for