Rare-earth pnictides and chalcogenides from first-principles.

This review tries to establish what is the current understanding of the rare-earth monopnictides and monochalcogenides from first principles. The rock salt structure is assumed for all the compounds in the calculations and wherever possible the electronic structure/properties of these compounds, as obtained from different ab initio methods, are compared and their relation to the experimental evidence is discussed. The established findings are summarised in a set of conclusions and provide outlook for future study and possible design of new materials.

Complex Magnetism of Lanthanide Intermetallics and the Role of their Valence Electrons: Ab Initio Theory and Experiment.

We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab initio electronic structure theory which includes disordered local moments and strong f-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with a pressure of +1.5 K kbar(-1) for GdCd confirmed by our experimental measurements of +1.6 K kbar(-1). Moreover, we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by noncollinear, canted magnetic order at low temperatures. Replacing 35% of the Mg atoms with Zn removes this transition, in excellent agreement with long-standing experimental data.

Phase transitions in rare earth tellurides under pressure.

Using first-principles calculations we have studied the valence and structural transitions of the rare earth monotellurides RTe (R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) under pressure. The self-interaction corrected local spin-density approximation is used to establish the ground state valence configuration as a function of volume for the RTe in both the NaCl (B1) and CsCl (B2) structures. We find that in ambient conditions all the RTe are stabilized in the B1 structure. A trivalent (R(3+)) rare earth ground state is predicted for the majority of the RTe, with the exception of SmTe, EuTe, DyTe, TmTe and YbTe, where the fully localized divalent (R(2+)) rare earth configuration is found to be energetically most favourable. Under pressure, the trivalent RTe undergo structural transitions to the B2 structure without associated valence transition. The divalent RTe on the other hand are characterized by a competition between the structural and electronic degrees of freedom, and it is the degree of f-electron delocalization that determines the sequence of phase transitions. In EuTe and YbTe, where respectively the half-filled and filled shells result in a very stable divalent configuration, we find that it is the structural B1 â†’ B2 transition that occurs first, followed by the R(2+) â†’ R(3+) valence transition at even higher pressures. In SmTe, DyTe and TmTe, the electronic transition occurs prior to the structural transition. With the exception of YbTe, the calculated transition pressures are found to be in good agreement with experiment.

Self-interaction correction in multiple scattering theory: application to transition metal oxides.

We apply to transition metal monoxides the self-interaction corrected (SIC) local spin density approximation, implemented locally in the multiple scattering theory within the Korringa-Kohn-Rostoker (KKR) band structure method. The calculated electronic structure and in particular magnetic moments and energy gaps are discussed in reference to the earlier SIC results obtained within the linear muffin-tin orbital atomic sphere approximation band structure method, involving transformations between Bloch and Wannier representations, in order to solve the eigenvalue problem and calculate the SIC charge and potential. Since the KKR method can be easily extended to treat disordered alloys, by invoking the coherent potential approximation (CPA), in this paper we compare the CPA approach and supercell calculations to study the electronic structure of NiO with cation vacancies.

Lanthanide contraction and magnetism in the heavy rare earth elements.

The heavy rare earth elements crystallize into hexagonally close packed (h.c.p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have. These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice. Such incommensurate ordering is associated with a 'webbed' topology of the momentum space surface separating the occupied and unoccupied electron states (the Fermi surface). The shape of this surface-and hence the magnetic structure-for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h.c.p. lattice. A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction, where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.

Superconductivity in lithium, potassium, and aluminum under extreme pressure: a first-principles study.

Extreme pressure strongly affects the superconducting properties of "simple" elemental metals, such as Li, K, and Al. Pressure induces superconductivity in Li (as high as 17 K) while suppressing it in Al. We report first-principles investigations of the superconducting properties of dense Li, K, and Al based on a recently proposed, parameter-free, method. Our results show an unprecedented agreement with experiments, assess the predictive power of the method over a wide range of densities and electron-phonon couplings, and provide predictions for K, where no experiments exist so far. More importantly, our results help uncover the physics of the different behaviors of Li and Al in terms of phonon softening and Fermi surface nesting in Li.

Weakly dispersive band near the fermi level of GaMnAs due to Mn interstitials.

The nature of the weakly dispersive electronic band near the Fermi level observed in photoemission experiments on the diluted magnetic semiconductor GaMnAs is investigated theoretically. The combination of experimental features appears puzzling. We show that the formation of the band is closely related to the presence of the Mn interstitial impurities. The states forming the band have predominantly minority-spin Mn-3d character. The low experimental Mn-3d intensity is explained by the low content of the interstitial Mn impurities. The features of the band are robust with respect to the calculational technique [local density approximation (LDA), LDA + U].

Superconducting properties of MgB2 from first principles.

Solid MgB(2) has rather interesting and technologically important properties, such as a very high superconducting transition temperature. Focusing on this compound, we report the first nontrivial application of a novel density-functional-type theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, we obtain the transition temperature, the gaps, and the specific heat of MgB(2) in very good agreement with experiment. Moreover, our calculations show how the Coulomb interaction acts differently on sigma and pi states, thereby stabilizing the observed superconducting phase.

[Sexuality and partnership aspects of Parkinson disease. Results of an empirical study of patients and their partners] . / Sexualität und Partnerschaft bei Morbus Parkinson. Ergebnisse einer empirischen Studie bei Betroffenen und ihren Partnern.

In a retrospective, non-randomised cross-sectional study the influence of Parkinson's Disease (PD) on sexuality and partnership in 2099 affected members of the German Parkinson Organization (dPV) were investigated. At an average age of 65, 330 women and 1008 men had been living in partnership for an average of 37 years. Not only sexual dysfunctions occurred both in affected women and men but also an evident reduction of sexual contentment on the whole. The affected patients mentioned specific symptoms of PD and medication as the decisive factors of influence on their sexuality. It was impressive that one single group of substances could influence sexual functions by increasing as well as decreasing them or having no influence at all. Furthermore different sexes in different genders became obvious. The information concerning their partnership situation given by both men and women shows that communication in general, especially caressing and showing feelings, are reduced since diagnosis, whereas a desire for mutual intimacy prevails on the same level as before.

[Effect of topical anaesthesic drops, measured by aesthesiometry (author's transl)]. / Zur Wirkung von Oberflächenanästhetika am Auge.

By means of a new electronic-optical instrument corneal sensitivity after application of topical anaesthesia was examined. In a prospective study different preparations were compared, also the influence of concentration dosage and milieu were studied.