Finite-difference method for the calculation of X-ray spectroscopies

International audienc

The FDMNES code

International audienc

Large orbital magnetic moment in Pt 13

We present an extensive study of Pt13 clusters embedded in a Na-Y zeolite, by comparing calculations for isolated clusters to experimental data. We perform structural refinements for various geometries involving the isolated clusters and calculate the corresponding x-ray absorption and magnetic circular dichroism spectra, from the joint perspective of pseudopotential plane wave calculations and real space multiple scattering theory. Taking into account the spin-orbit coupling significantly improves the previous scalar relativistic predictions of magnetic properties. The ensemble of embedded Pt13 is found to be dominated by a non-magnetic cuboctahedral geometry. One of the implications is that the ground state of Pt13 clusters in the zeolite environment is different from that of isolated particles. We investigate several isomers that yield a magnetic signature. Furthermore, their abundance was estimated by direct comparison with experiment. We found that one third of the magnetic moment of Pt13 comes from the orbital contribution, in agreement with the experimental value. We therefore provide theoretical proof of the extraordinary orbital magnetization in Pt13 clusters. © 2014 IOP Publishing Ltd.We acknowledge financial support from Ministerio de Economia y Competitividad (MINECO MAT2011/23791) and Aragonese IMANA projects, partially funded by the Fondo Europeo de Desarollo Regional program and the European Social Fund.Peer Reviewe

Superb water splitting activity of the electrocatalyst Fe3Co(PO4)(4) designed with computation aid

For efficient water splitting, it is essential to develop inexpensive and super-efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, we report a phosphate-based electrocatalyst [Fe3Co(PO4)(4)@reduced-graphene-oxide(rGO)] showing outstanding OER performance (much higher than state-of-the-art Ir/C catalysts), the design of which was aided by first-principles calculations. This electrocatalyst displays low overpotential (237 mV at high current density 100 mA cm(-2) in 1M KOH), high turnover frequency (TOF: 0.54 s(-1)), high Faradaic efficiency (98%), and long-term durability. Its remarkable performance is ascribed to the optimal free energy for OER at Fe sites and efficient mass/charge transfer. When a Fe3Co(PO4)(4)@rGO anodic electrode is integrated with a Pt/C cathodic electrode, the electrolyzer requires only 1.45 V to achieve 10 mA cm(-2) for whole water splitting in 1M KOH (1.39 V in 6 M KOH), which is much smaller than commercial Ir-C//Pt-C electrocatalysts. This cost-effective powerful oxygen production material with carbon-supporting substrates offers great promise for water splitting