Experimentally, the intermetallic compound Mn$_{4}$FeGe$_{3}$ has been recently shown to exhibit enhanced magnetic properties and spin polarization compared to the Mn$_{5}$Ge$_{3}$ parent compound. The present {\em ab-initio} study focusses on the effect of Fe substitution on the electronic and magnetic properties of the compound. Our calculations reveal that the changes on the Fermi surface of the doped compound are remarkable and provide explanations for the enhanced spin-polarization observed. Finally, we show that it is indeed possible to tune the degree of spin-polarization upon Fe doping, thus making the Mn$_{1-x}$Fe$_{x}$Ge$_{3}$ intermetallic alloy very promising for future spintronic applications.
This paper presents an approach for optical absorption calculations based on nonempirical dielectric-dependent hybrid functionals with an accuracy similar to the Bethe-Salpeter equation but at a dramatically reduced cost. This approach relies on the consistent use of a spatially dependent screening of the Coulomb interaction in the functional and in the calculation of the spectra
The atomic structure of the most stable reconstructed surface of cuprous oxide (Cu$_{2}$O)(111) surface has been a longstanding topic of debate. In this study, we develop on-the-fly machine-learned force fields (MLFFs) to systematically investigate the various reconstructions of the Cu$_{2}$O(111) surface under stoichiometric as well as O- and Cu-deficient or rich conditions, focusing on both ($\sqrt{3}$$\times$$\sqrt{3}$)R30° and (2$\times$2) supercells. By utilizing parallel tempering simulations supported by MLFFs, we confirm that the previously described nanopyramidal and Cu-deficient (1$\times$1) structures are the lowest energy structures from moderately to strongly oxidizing conditions. In addition, we identify two promising nanopyramidal reconstructions at highly reducing conditions, a stoichiometric and a Cu-rich one. Surface energy calculations performed using spin-polarized PBE, PBE+U, r$^{2}$SCAN, and HSE06 functionals show that the previously known Cu-deficient configuration and nanopyramidal configurations are at the convex hull (and, thus, equilibrium structures) for all functionals, whereas the stability of the other structures depends on the functional and is therefore uncertain. Our findings demonstrate that on-the-fly trained MLFFs provide a simple, efficient, and rapid approach to explore the complex surface reconstructions commonly encountered in experimental studies, and also enhance our understanding of the stability of Cu$_{2}$O(111) surfaces.
By performing accurate ab-initio density functional theory calculations, we study the role of $4f$ electrons in stabilizing the magnetic-field-induced ferroelectric state of DyFeO$_{3}$. We confirm that the ferroelectric polarization is driven by an exchange-strictive mechanism, working between adjacent spin-polarized Fe and Dy layers, as suggested by Y. Tokunaga [Phys. Rev. Lett, \textbf{101}, 097205 (2008)]. A careful electronic structure analysis suggests that coupling between Dy and Fe spin sublattices is mediated by Dy-$d$ and O-$2p$ hybridization. Our results are robust with respect to the different computational schemes used for $d$ and $f$ localized states, such as the DFT+$U$ method, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional and the GW approach. Our findings indicate that the interaction between the $f$ and $d$ sublattice might be used to tailor ferroelectric and magnetic properties of multiferroic compounds.
It is well known that the physical properties of some transition-metal compounds (mostly oxides) are strongly affected by intra-atomic correlations. Very recently, investigations of the adsorption of small molecules such as CO on the surfaces of transition-metal oxides have led to rather surprising results: the weak adsorbate-substrate bonding and the asymmetric (tilted) adsorption geometries contrast sharply the strong bonding and symmetric geometries characteristic for metallic surfaces. Calculations based on either Hartree-Fock or density-functional methods have failed to explain these observations. For bulk transition-metal oxides it has been demonstrated that the addition of a Hubbard-type on-site Coulomb repulsion U to the local-density Hamiltonian leads to an improved description of the electronic structure of these materials, but a consistent description of all physical properties proved to be elusive. In the present work, we present a comprehensive investigation of bulk NiO and of clean and CO-covered NiO(100) surfaces. We demonstrate that adding the on-site Coulomb repulsion to the spin-polarized gradient-corrected density-functional Hamiltonian leads to a consistently improved description of a wide range of cohesive, electronic, and magnetic properties of NiO (bulk and surface) and a very accurate description of the adsorption properties of CO. The effects of the strong electronic correlations in the substrate on the adsorbate-substrate bonding are discussed in detail.
The morphology, structure, and reactivity of vanadium oxide-decorated Pd(111) surfaces, which have been subjected to oxidation and reduction treatments, have been investigated by scanning tunneling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and high-resolution X-ray photoelectron spectroscopy (HR-XPS) with synchrotron radiation combined with ab initio density functional theory (DFT) calculations. Two major oxide phases form on the Pd(111) surface following the oxidation (V5O14) and reduction (s-V2O3) treatments; their structures have been revealed with the help of the DFT calculations. The reactive sites of both oxidized and reduced vanadium oxide/Pd(111) surfaces have been studied using the adsorption of CO as a test molecule for probing the free Pd sites. The adsorbate (C 1s) and substrate (Pd 3d) core level XPS data show that on the reduced, s-V2O3-decorated Pd(111) surfaces, CO occupies the same adsorption sites as on the clean Pd(111). In contrast, a new type of CO adsorption site is found on the oxidized, V5O14-covered Pd(111) surfaces that is associated with the adsorption of CO within the open (4 × 4) oxide lattice. The latter contains holes with six free Pd atoms per unit cell, which may be considered as a particular kind of an "adsorption pocket".
By performing accurate ab initio density functional theory (DFT) calculations, we study the role of 4f electrons in stabilizing the magnetic-field-induced ferroelectric state of DyFeO3. We confirm that the ferroelectric polarization is driven by an exchange-strictive mechanism, working between adjacent spin-polarized Fe and Dy layers, as suggested by Y Tokunaga (2008 Phys. Rev. Lett. 101 097205). A careful electronic structure analysis suggests that coupling between Dy and Fe spin sublattices is mediated by Dy–d and O–2p hybridization. Our results are robust with respect to the different computational schemes used for d and f localized states, such as the DFT+U method, the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional and the GW approach. Our findings indicate that the interaction between the f and d sublattices might be used to tailor the ferroelectric and magnetic properties of multiferroic compounds.
