From rst-principles calculations, we investigate the structural instabilities of CaMnO3. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground-state, the cubic perovskite structure of CaMnO3 also exhibit a weak ferroelectric instability.Although ferroelectricity is suppressed by antiferrodistortive oxygen motions, we show that it can be favored using strain or chemical engineering in order to make CaMnO3 multiferroic. We nally highlight that the FE instability of CaMnO3 is Mn-dominated. This illustrates that, contrary to the common believe, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation.

We consider spin dynamics for implementation in an atomistic framework and we address the feasibility of capturing processes in the femtosecond regime by inclusion of moment of inertia. In the spirit of an s-d-like interaction between the magnetization and electron spin, we derive a generalized equation of motion for the magnetization dynamics in the semiclassical limit, which is nonlocal in both space and time. Using this result we retain a generalized Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and demonstrate how the exchange interaction, damping, and moment of inertia, all can be calculated from first principles.

The d-band center model of Hammer and Nørskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH3 molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions.

Most stable structures and physical properties are studied for silicon-doped Al 13 , Al 19 , and Al 23 clusters using the ab initio molecular-dynamics method within the framework of a plane-wave pseudopotential approach and the local density as well as the generalized gradient approximations. The lowest energy structures of the undoped clusters are found to be Jahn-Teller distorted icosahedron, double icosahedron, and decahedron, respectively. Substitutional doping with a Si impurity makes these clusters electronically closed shell and leads to a large gain in the binding energy, which decreases with an increase in the cluster size in a nonmonotonic way. The heat of solution of a Si atom in clusters is found to be exothermic as compared to endothermic behavior in bulk aluminum. Further, a Si impurity is found to stabilize the Al 18 Si cluster in cuboctahedral structure. However, a capped icosahedron as well as a double icosahedron are found to be nearly degenerate with about 1.77 eV higher binding energy. For Al 22 Si, the decahedral isomer has the lowest energy with a highest-occupied lowest-unoccupied molecular-orbital gap of 0.82 eV. It is also found to be very stable when heated at 700 K. Similar results are likely to hold in the case of doping with germanium. We discuss the significance of these results for the understanding of the stability of silicon-doped quasicrystals.

In Pt-transition metal (TM) alloy catalysts, the electron transfer from the TM to Pt is retarded owing to the inevitable oxidation of the TM surface by oxygen. In addition, acidic electrolytes such as those employed in fuel cells accelerate the dissolution of the surface TM oxide, which leads to catalyst degradation. Herein, we propose a novel synthesis strategy that selectively modifies the electronic structure of surface Co atoms with N-containing polymers, resulting in highly active and durable PtCo nanoparticle catalysts useful for the oxygen reduction reaction (ORR). The polymer, which is functionalized on carbon black, selectively interacts with the Co precursor, resulting in Co-N bond formation on the PtCo nanoparticle surface. Electron transfer from Co to Pt in the PtCo nanoparticles modified by the polymer is enhanced by the increase in the difference in electronegativity between Pt and Co compared with that in bare PtCo nanoparticles with the TM surface oxides. In addition, the dissolution of Co and Pt is prevented by the selective passivation of surface Co atoms and the decrease in the O-binding energy of surface Pt atoms. As a result, the catalytic activity and durability of PtCo nanoparticles for the ORR are significantly improved by the electronic ensemble effects. The proposed organic/inorganic hybrid concept will provide new insights into the tuning of nanomaterials consisting of heterogeneous metallic elements for various electrochemical and chemical applications.