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Defects and impurities strongly dictate the physical properties of materials by tuning conductivity, modulating magnetic response, and changing optical properties. Here we analyze how these entities behave in the prototype quantum material ${\mathrm{FeGa}}_{3}$. We have studied its intrinsic defects (vacancies, antisites, and interstitials) as well as different types of dopants such as Zn, Mn, Ge, Co, In, and Ru. Intrinsic defects are shown to have large formation energies, whereas dopants have a larger solubility. Different electronic and magnetic states, including localized polarons, were found to be induced by specific defect charge states, significantly altering the properties of the host material.

Epitaxial bilayer silicon oxide is a transferable two-dimensional material predicted to be a wide band gap semiconductor, with potential applications for deep UV optoelectronics, or as a building block of van der Waals heterostructures. The prerequisite to any sort of such applications is the knowledge of the electronic band structure, which we unveil using angle-resolved photoemission spectroscopy and rationalize with the help of density functional theory (DFT) calculations. We discover dispersing bands related to electronic delocalization within the top and bottom planes of the material, with two linear crossings reminiscent of those predicted in bilayer AA-stacked graphene, and semi-flat bands stemming from the chemical bridges between the two planes. This band structure is robust against exposure to air, and can be controlled by exposure to oxygen. We provide an experimental lower-estimate of the band gap size of 5 eV and predict a full gap of 7.36 eV using DFT calculations.

IrGa

Tungsten trioxide (WO) is a compound that has a high degree of polymorphism, but a detailed phase diagram of this material is not available in the literature and a systematic ab-initio study including all its crystallographic phases does not exist. In this work, we have performed a first-principles density functional theory study of all WO crystalline phases within the generalized gradient and hybrid approximations of the exchange–correlation functional. We have calculated the equations of state, the isothermal bulk moduli, the -centered vibrational frequencies, and the phase diagram using the Debye–Einstein model. The calculated phase diagram shows only the crystallographic phase transition at high pressure and low temperature, being the -phase the stable polymorph at room temperature and ambient pressure, and the -phase stable at low temperatures and high pressures. In addition, the band structures were calculated observing a variation of the energy gap between 1.76 up to 2.79 eV with a similar topology of the top valence and bottom conduction bands across all the polymorphs.

We perform an ab initio study of the electronic structure and magnetic properties of 3d, 4d and 5d transition metals (TM) adsorbed on freestanding and Ag(1 1 1)-supported [Formula: see text]-borophene. The stability of TM adsorption is high for all atoms and increases with the period. For the 3d TM adsorption we observed strong exchange effects. The Ag(1 1 1)-surface induced small effects on the calculated properties. Studying the magnetic interaction between TMs, VIB atoms showed direct exchange, while VIIB and Fe showed 2p(B)-mediated indirect exchange. In the ultimate case of a one-dimensional TM array, Ru and Os also show direct exchange effects.

IrGa3 is an intermetallic compound which is expected to be a metal, but a study on the electronic properties of this material to confirm its metallic character is not available in the literature. In this work, we report for the first time a first-principles density functional theory and semiclassical Boltzmann theory study of the structural, electronic and transport properties of this material. The inclusion of the spin–orbit coupling term is crucial to calculate accurately the electronic properties of this compound. We have established that IrGa3 is an indirect semiconductor with a narrow gap of 0.07 eV. From semiclassical Boltzmann transport theory, it is inferred that this material, with the appropriate hole concentration, could have a thermoelectric figure of merit at room temperature comparable to other intermetallic compounds such as FeGa3, though the transport properties of IrGa3 are highly anisotropic.

FeGa$_3$ is an unusual intermetallic semiconductor that presents intriguing magnetic responses to the tuning of its electronic properties. When doped with Ge, the system evolves from diamagnetic to paramagnetic to ferromagnetic ground states that are not well understood. In this work, we have performed a joint theoretical and experimental study of FeGa$_{3-x}$Ge$_x$ using Density Functional Theory and magnetic susceptibility measurements. For low Ge concentrations we observe the formation of localized moments on some Fe atoms and, as the dopant concentration increases, a more delocalized magnetic behavior emerges. The magnetic configuration strongly depends on the dopant distribution, leading even to the appearance of antiferromagnetic interactions in certain configurations., See "Note added to arXiv version" in text

We perform an ab initio study of the electronic structure and magnetic properties of 3d, 4d and 5d transition metals (TM) adsorbed on freestanding and Ag(1 1 1)–supported –borophene. The stability of TM adsorption is high for all atoms and increases with the period. For the 3d TM adsorption we observed strong exchange effects. The Ag(1 1 1)–surface induced small effects on the calculated properties. Studying the magnetic interaction between TMs, VIB atoms showed direct exchange, while VIIB and Fe showed 2p(B)–mediated indirect exchange. In the ultimate case of a one-dimensional TM array, Ru and Os also show direct exchange effects.

Crystalline 2D boron sheets, known as borophene, are the most recently-discovered type of 2D materials, and very little is known about them. Different configurations of borophene have been reported stable when grown on Ag(1 1 1) surface under well controlled conditions. One of this configurations is partially oxidized while the other one remains quite inert to oxidation when exposed to ambient conditions. In this work, the oxidation process of the free-standing and Ag(1 1 1)-supported borophene is modeled using first-principles calculations based on density functional theory (DFT). On the free-standing case, the oxygen molecule may go through a triplet to singlet transition, followed by a barrierless oxidation process. This transition is not observed upon the presence of the Ag(1 1 1) surface, what accelerates the oxidation process. We also propose that the different structures of borophene reported in the literature can be understood by this oxidation process. Oxidation of the buckled structure could induce the planar structure with an ordered distribution of vacancies.