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The challenges imposed by climate change require the continued improvement and identification of materials for the development of green technologies. Point defect engineering is a promising technology for producing green hydrogen by taking advantage of catalytic hydrogen evolution reactions. In this work, we investigate the role of anionic and cationic vacancy point defects, as well as the nature of the active sites, in the catalytic activation of Cu2WS4 single layers. The stability of the pristine and defective structures of Cu2WS4 has been thoroughly investigated using density-functional theory calculations. A deep analysis of the formation enthalpy indicates that the Cu vacancy is the chemically most favorable vacancy. However, the calculated adsorption energy indicates that the presence of such vacancies slightly enhances the hydrogen evolution reaction. In contrast, the formation of an S vacancy considerably magnifies the same reaction in Cu2WS4 single layers.

We present detailed studies of the high-field magnetoresistance of the layered organic metal κ-(BETS)2Mn- [N(CN)2]3 under a pressure slightly above the insulator-metal transition. The experimental data are analyzed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the in-plane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obtained effective cyclotron masses with the calculated band masses reveals electron correlations significantly dependent on the electron momentum. The momentum- or band-dependent mobility is also reflected in the behavior of the classical magnetoresistance anisotropy in a magnetic field parallel to layers. Other characteristics of the conducting system related to interlayer charge transfer and scattering mechanisms are discussed based on the experimental data. Besides the known high-field effects associated with the Fermi surface geometry, new pronounced features have been found in the angle-dependent magnetoresistance, which might be caused by coupling of the metallic charge transport to a magnetic instability in proximity to the metal-insulator phase boundary., We are grateful to N.D. Kushch for providing the high-quality crystals for our studies and to P.D. Grigoriev for numerous useful discussions. The work was supported by the German Research Foundation (DFG) via the Grant No. KA 1652/4-1. The high-field measurements were done under support of the LNCMI-CNRS, member of the European Magnetic Field Laboratory (EMFL). V.N.Z. acknowledges the support from RFBR Grant No. 18-02-00280. Work in Spain was supported by the Spanish Ministerio de Economa y Competitividad (Grants No. FIS2015-64886-C5-4-P and No. CTQ2015-64579-C3-3-P) and Generalitat de Catalunya (2017SGR1506, 2017SGR1289, and XRQTC). E.C. acknowledges support from the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2015-0496. P.A. acknowledges support from the Maria de Maeztu Units of Excellence Program under Grant No. MDM-2017-0767.

We study the effect that a statically screened Coulomb potential represented by a Debye-Hückel-Yukawa potential has in the electronic structure of the simplest molecule H2+ within the Born-Oppenheimer approximation. The method of solution is based on a two-center partial-wave expansion expressed in confocal elliptic coordinates using B-spline polynomials. General algorithms for the computation of energies, wave functions, and dipole and nonadiabatic radial matrix elements are given in detail. As it occurs in atoms, screening in simple molecules shifts the energies of bound states upwards so that, as screening increases, every bound state eventually crosses the upper ionization threshold at a critical screening value. The loss of long-range Coulomb interactions has its effect in the structure of wave functions, and consequently in the dipole and nonadiabatic matrix elements at intermediate and long internuclear distances, which determine the dynamics in external electromagnetic fields and collisional processes. Other issues related to a practical solution of the arbitrary sign problem, as well as the assignment of angular and radial nodes to the variational eigenfunctions, and the appearance of molecular shape resonances and Borromean states in H2+ as screening increases, are also addressed in this work, Work supported by the Advanced Grant of the European Research Council XCHEM 290853, the European COST Action XLIC CM1204, and the MINECO Project No. FIS2013-42002-R. A.F.O.-L. acknowledges financial support from EACEA through an Erasmus Mundus scholarship. J.L.S.-V. acknowledges financial support from Vicerrectoria de investigacion at Universidad de Antioquia (Contract No. E01538 and Estrategia de Sostenibilidad 2016-2017) and from Departamento Administrativo de Ciencia, Tecnologia e Innovacion (COLCIENCIAS, Colombia) under Contract No.111565842968

A general mapping between the energy of pertinent magnetic solutions and the diagonal terms of the spin Hamiltonian in a local representation provides the first general framework to extract accurate values for the many body terms of extended spin Hamiltonians from periodic first-principle calculations. Estimates of these terms for La2CuO4, the paradigm of high-Tc superconductor parent compounds, and for the SrCu2O3 ladder compound are reported. For La2CuO4, present results support experimental evidence by Toader et al. [Phys. Rev. Lett. 94, 197202 (2005)10.1103/PhysRevLett.94.197202]. For SrCu2O3 even larger four-body spin amplitudes are found together with Jl/Jr = 1 and non-negligible ferromagnetic interladder exchange.

10 pages, 13 figures, 3 tables., Differential scanning calorimetry experiments have been performed under magnetic field in RCo2 Laves phases compounds (R=Pr, Nd, Tb, Dy, Ho, and Er). The thermodynamical nature of the ferromagnetic transitions in PrCo2 and NdCo2 is clarified, after the controversy present in the literature about the character of their ordering transitions. The magnetocaloric effect in the compounds showing a first-order magnetostructural transition (R=Dy, Ho, and Er)is characterized. The latent heat, L, and the entropy change at the transition, S, have been studied by inducing the transition sweeping the temperature at a constant field and sweeping the field at a constant temperature. Results from calorimetric data show that L is essentially temperature independent, suggesting that the first order transitions in RCo2 are dominated by the structural effects. The magnetocaloric effect has been also characterized from magnetization data and the results are in excellent agreement with those from calorimetric data. However, the corresponding values of S for isothermal and isofield experiments differsignificantly. We interpret the differences in terms of the broadness of the transitions and prove that the various S values reported in literature for first-order transitions are not always directly comparable., This work has been partially funded by the Fundación Areces, the Spanish CICYT research Projects Nos. MAT2002-04178-C04-03, MAT2005-002454, and MAT2003-01124, the FEDER program, the Aragonese CAMRADS research group, and the Catalan DURSI research Project No. 2001SGR00066.We thank N. Plugaru and M. J. Pastor for sample preparation, Ll. Mañosa, A. Planes, and L. Morellón for fruitful discussions, J. Rodríguez and J. Sánchez-Marcos for their magnetization facilities at the Universidad de Cantabria, and J. Bartolomé for a critical reading of the manuscript. J.H. acknowledges MEC for the Ph.D. grant.

Oxygen vacancies in metal oxides are known to determine their chemistry and physics. The properties of neutral oxygen vacancies in metal oxides of increasing complexity (MgO, CaO, alpha-Al2O3, and ZnO) have been studied using density functional theory. Vacancy formation energies, vacancy-vacancy interaction, and the barriers for vacancy migration are determined and rationalized in terms of the ionicity, the Madelung potential, and lattice relaxation. It is found that the Madelung potential controls the oxygen vacancy properties of highly ionic oxides whereas a more complex picture arises for covalent ZnO.

We report on a growth study of MgO films deposited on Al2O3(0001) substrates by magnetron sputtering. The films exhibited a preferred rocksalt MgO(111) orientation. Surprisingly, depending on the O2 gas flow ratio, a structure of graphiticlike wurtzite MgO(0001) has been revealed. The observed Mg-O perpendicular bond length reduction is accompanied by an atomically flat surface morphology for the development of MgO(111) films; the transition to the bulk rocksalt structure occurs in the 3-6 nm coverage range. Previously, relaxation of the electrostatic instability of MgO(111) films accompanied by an in-plane lattice increase has been suggested theoretically [Phys. Rev. Lett. 98, 205701 (2007)]. Here, relying on ab initio calculations, we infer that Mg vacancies facilitate the lattice match with the substrate. This mechanism suggests methods to engineer oxide heterostructures.

We illustrate how to apply modern effective field theory techniques and dimensional regularization to factorise the various scales which appear in QED bound states at finite temperature. We focus here on the muonic hydrogen atom. Vacuum polarization effects make the physics of this atom at finite temperature very close to that of heavy quarkonium states. We comment on the implications of our results for these states in the quark gluon plasma. In particular, we estimate the effects of a finite charm quark mass in the dissociation temperature of bottomonium., 22 pages, 8 figures. Journal version, reference added

The physical contributions to the KNiF 3 magnetic exchange coupling integral have been obtained from specially designed ab initio cluster model calculations. Three important mechanisms have been identified. These are the delocalization of the magnetic orbitals into the anion «p» band, the variational contribution of the second-order interactions, and the many-body terms «hidden» in the two-body operator of the Heisenberg Hamiltonian

The first observation of the elusive Fe4+ charge state coming from the nuclear decay of 57Co3+ has been found in the Mössbauer emission spectra of 57Co:La2Li0.5Co0.5O4. A Ti-doped sample was prepared in order to show that the Fe4+ fraction can be conveniently monitored. Both results were predicted on the basis of the electronic energy-band scheme of these oxides.