94 research outputs found
The AFLOW Fleet for Materials Discovery
The traditional paradigm for materials discovery has been recently expanded
to incorporate substantial data driven research. With the intent to accelerate
the development and the deployment of new technologies, the AFLOW Fleet for
computational materials design automates high-throughput first principles
calculations, and provides tools for data verification and dissemination for a
broad community of users. AFLOW incorporates different computational modules to
robustly determine thermodynamic stability, electronic band structures,
vibrational dispersions, thermo-mechanical properties and more. The AFLOW data
repository is publicly accessible online at aflow.org, with more than 1.7
million materials entries and a panoply of queryable computed properties. Tools
to programmatically search and process the data, as well as to perform online
machine learning predictions, are also available.Comment: 14 pages, 8 figure
Small Polarons in Transition Metal Oxides
The formation of polarons is a pervasive phenomenon in transition metal oxide
compounds, with a strong impact on the physical properties and functionalities
of the hosting materials. In its original formulation the polaron problem
considers a single charge carrier in a polar crystal interacting with its
surrounding lattice. Depending on the spatial extension of the polaron
quasiparticle, originating from the coupling between the excess charge and the
phonon field, one speaks of small or large polarons. This chapter discusses the
modeling of small polarons in real materials, with a particular focus on the
archetypal polaron material TiO2. After an introductory part, surveying the
fundamental theoretical and experimental aspects of the physics of polarons,
the chapter examines how to model small polarons using first principles schemes
in order to predict, understand and interpret a variety of polaron properties
in bulk phases and surfaces. Following the spirit of this handbook, different
types of computational procedures and prescriptions are presented with specific
instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure
Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4
Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration
Reversible Control of Magnetic Interactions by Electric Field in a Single Phase Material
Intrinsic magnetoelectric coupling describes the interaction between magnetic
and electric polarization through an inherent microscopic mechanism in a single
phase material. This phenomenon has the potential to control the magnetic state
of a material with an electric field, an enticing prospect for device
engineering. We demonstrate 'giant' magnetoelectric cross-field control in a
single phase rare earth titanate film. In bulk form, EuTiO3 is
antiferromagnetic. However, both anti and ferromagnetic interactions coexist
between different nearest neighbor europium ions. In thin epitaxial films,
strain can be used to alter the relative strength of the magnetic exchange
constants. Here, we not only show that moderate biaxial compression
precipitates local magnetic competition, but also demonstrate that the
application of an electric field at this strain state, switches the magnetic
ground state. Using first principles density functional theory, we resolve the
underlying microscopic mechanism resulting in the EuTiO3 G-type magnetic
structure and illustrate how it is responsible for the 'giant' cross-field
magnetoelectric effect
Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX 2 (X = S, Se and Te)
We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (Xâ=âS, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20âeV, all with integer magnetic moments of 1.0âÎŒB. The GGA plus on-site Coulomb interaction U (GGAâ+âU) enhances the exchange splittings and raises the energy gap up to 0.38~0.65âeV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7âeV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6âeV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553âK for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics
Surface states on NiO (100) and the origin of the contrast reversal in atomically resolved scanning tunneling microscope images
Formation of the Face-Centered Cubic (FCC)-NdO x Phase at Nd/Nd-Fe-B Interface: A First-Principles Modeling
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