C. Franchini

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.

Superconducting Properties ofMgB2from 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.

Ru doping in iron-based pnictides: The “unfolded” dominant role of structural effects for superconductivity

We present an ab initio study of Ru substitution in two different compounds,

Electronic structure of PbFe1/2Ta1/2O3: Crystallographic ordering and magnetic properties

{mathrm{BaFe}}_{2}{mathrm{As}}_{2}

Superconducting properties of MgB2 from first principles

and LaFeAsO, pure and F doped. Despite the many similarities among them, Ru substitution has very different effects on these compounds. By means of an unfolding technique, which allows us to trace back the electronic states into the primitive cell of the pure compounds, we are able to disentangle the effects brought by the local structural deformations and by the impurity potential to the states at the Fermi level. Our results are compared with available experiments and show (i) satisfying agreement of the calculated electronic properties with experiments, confirming the presence of a magnetic order on a short-range scale, and (ii) Fermi surfaces strongly dependent on the internal structural parameters, more than on the impurity potential. These results enter a widely discussed field in the literature and provide a better understanding of the role of Ru in iron pnictides: although isovalent to Fe, the Ru-Fe substitution leads to changes in the band structure at the Fermi level mainly related to local structural modifications.