80 research outputs found
Review of the Structural Stability, Electronic and Magnetic Properties of Nonmetal-Doped TiO from First-Principles Calculations
This paper reviews and summarizes the recent first-principles theoretical
studies of the structural stability, electronic structure, optical and magnetic
properties of nonmetal-doped TiO. The first section presents a comparison
study of the structural stability for X-anion and X-cation doped TiO (X=B,
C, Si, Ge, N, P, As, Sb, S, Se, Te, F, Cl, Br, and I), which reveals that the
sites of nonmetal dopants (i.e., at O sites or at Ti sites) in TiO are
determined by the growth condition of doped TiO and the dopants'
electronegativities. The next section reviews the electronic structure, optical
absorption and mechanism of the visible-light photocatalytic activity for
nonmetal-doped TiO. The third section summarizes the origin of the
spin-polarization and the magnetic coupling character in C- (N- and B-) doped
TiO.Comment: 21 pages, 24 figures, 3 table
Density functional characterization of the antiferromagnetism in oxygen-deficient anatase and rutile TiO2
We present theoretical evidence for local magnetic moments on Ti3+ ions in
oxygen-deficient anatase and rutile TiO2 observed in a recent experiment [S.
Zhou, et al., Phys. Rev. B 79, 113201 (2009)]. Results of our first-principles
GGA+U calculations reveal that an oxygen vacancy converts two Ti4+ ions to two
Ti3+ ions in anatase phase, which results in a local magnetic moment of 1.0
per Ti3+. The two Ti3+ ions, however, form a stable antiferromagnetic
state, and similar antiferromagnetism is also observed in oxygen-deficient
rutile phase TiO2. The calculated results are in good agreement with the
experimentally observed antiferromagnetic-like behavior in oxygen-deficient
Ti-O systems.Comment: 16 pages, 5 figure
High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures.
The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO3 and SrTiO3 (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO3-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. Of these, Al-, Ga-, Sc-, and Ta-based compounds can form a 2DEG with STO, while In-based compounds exhibit a strain-induced strong polarization when deposited on STO substrate. In particular, the Ta-based compounds can form 2DEG with potentially high electron mobility at (TaO2)+/(SrO)0 interface. Our approach, by defining materials descriptors solely based on the bulk materials properties, and by relying on the perovskite-oriented quantum materials repository, opens new avenues for the discovery of perovskite-oxide-based functional interface materials in a HT fashion
A RESTful API for exchanging Materials Data in the AFLOWLIB.org consortium
The continued advancement of science depends on shared and reproducible data.
In the field of computational materials science and rational materials design
this entails the construction of large open databases of materials properties.
To this end, an Application Program Interface (API) following REST principles
is introduced for the AFLOWLIB.org materials data repositories consortium.
AUIDs (Aflowlib Unique IDentifier) and AURLs (Aflowlib Uniform Resource
locator) are assigned to the database resources according to a well-defined
protocol described herein, which enables the client to access, through
appropriate queries, the desired data for post-processing. This introduces a
new level of openness into the AFLOWLIB repository, allowing the community to
construct high-level work-flows and tools exploiting its rich data set of
calculated structural, thermodynamic, and electronic properties. Furthermore,
federating these tools would open the door to collaborative investigation of
the data by an unprecedented extended community of users to accelerate the
advancement of computational materials design and development.Comment: 22 pages, 7 figure
Origin of the different conductive behavior in pentavalent-ion-doped anatase and rutile TiO
The electronic properties of pentavalent-ion (Nb, Ta, and
I) doped anatase and rutile TiO are studied using spin-polarized
GGA+\emph{U} calculations. Our calculated results indicate that these two
phases of TiO exhibit different conductive behavior upon doping. For doped
anatase TiO, some up-spin-polarized Ti 3\emph{d} states lie near the
conduction band bottom and cross the Fermi level, showing an \emph{n}-type
half-metallic character. For doped rutile TiO, the Fermi level is pinned
between two up-spin-polarized Ti 3\emph{d} gap states, showing an insulating
character. These results can account well for the experimental different
electronic transport properties in Nb (Ta)-doped anatase and rutile TiO.Comment: 4 pages, 5 figure
QoE-Driven Video Transmission: Energy-Efficient Multi-UAV Network Optimization
This paper is concerned with the issue of improving video subscribers'
quality of experience (QoE) by deploying a multi-unmanned aerial vehicle (UAV)
network. Different from existing works, we characterize subscribers' QoE by
video bitrates, latency, and frame freezing and propose to improve their QoE by
energy-efficiently and dynamically optimizing the multi-UAV network in terms of
serving UAV selection, UAV trajectory, and UAV transmit power. The dynamic
multi-UAV network optimization problem is formulated as a challenging
sequential-decision problem with the goal of maximizing subscribers' QoE while
minimizing the total network power consumption, subject to some physical
resource constraints. We propose a novel network optimization algorithm to
solve this challenging problem, in which a Lyapunov technique is first explored
to decompose the sequential-decision problem into several repeatedly optimized
sub-problems to avoid the curse of dimensionality. To solve the sub-problems,
iterative and approximate optimization mechanisms with provable performance
guarantees are then developed. Finally, we design extensive simulations to
verify the effectiveness of the proposed algorithm. Simulation results show
that the proposed algorithm can effectively improve the QoE of subscribers and
is 66.75\% more energy-efficient than benchmarks
Effect of Electronegativity and Charge Balance on the Visible-Light-Responsive Photocatalytic Activity of Nonmetal Doped Anatase TiO 2
The origin of visible light absorption and photocatalytic activity of nonmetal doped anatase TiO2 were investigated in details in this work based on density functional theory calculations. Our results indicate that the electronegativity is of great significance in the band structures, which determines the relative positions of impurity states induced by the doping species, and further influences the optical absorption and photocatalytic activities of doped TiO2. The effect of charge balance on the electronic structure was also discussed, and it was found that the charge-balance structures may be more efficient for visible light photocatalytic activities. In addition, the edge positions of conduction band and valence band, which determine the ability of a semiconductor to transfer photoexcited electrons to species adsorbed on its surface, were predicted as well. The results may provide a reference to further experimental studies
Aimsgb: An algorithm and open-source python library to generate periodic grain boundary structures
An algorithm implemented in an open-source python library was developed for building periodic grain boundary models in a universal fashion. The software framework, aimsgb, aims to generate tilt and twist grain boundaries from an input cubic or non-cubic crystal structure for ab-initio and classical atomistic simulation. It can output a coincidence site lattice (CSL) grain boundary for a cubic input structure and a non-CSL grain boundary for a non-cubic input structure. This framework has two useful features: (i) it can calculate all the CSL matrices for generating CSL from a given Sigma (Σ) value and rotation axis, allowing the users to build the specific CSL and grain boundary models; (ii) it provides a convenient command line tool to enable high-throughput generation of tilt and twist grain boundaries by assigning an input crystal structure, Σ value, rotation axis, and grain boundary plane. The developed algorithm in the open-source python library is expected to facilitate studies of grain boundary in materials science. The software framework is available on the website: aimsgb.org
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