Showing papers by "David Vanderbilt published in 2016"
Ghent University1, Forschungszentrum Jülich2, Åbo Akademi University3, Aalto University4, Vienna University of Technology5, Duke University6, University of Grenoble7, École Polytechnique Fédérale de Lausanne8, Durham University9, International School for Advanced Studies10, Max Planck Society11, Uppsala University12, Fritz Haber Institute of the Max Planck Society13, Humboldt University of Berlin14, Technical University of Denmark15, National Institute of Standards and Technology16, University of Udine17, Université catholique de Louvain18, University of Basel19, Harvard University20, University of California, Davis21, Rutgers University22, University of York23, Wake Forest University24, Science and Technology Facilities Council25, University of Oxford26, University of Vienna27, Dresden University of Technology28, Leibniz Institute for Neurobiology29, Radboud University Nijmegen30, University of Tokyo31, Centre national de la recherche scientifique32, University of Cambridge33, Royal Holloway, University of London34, University of California, Santa Barbara35, University of Luxembourg36, Los Alamos National Laboratory37, Harbin Institute of Technology38
TL;DR: A procedure to assess the precision of DFT methods was devised and used to demonstrate reproducibility among many of the most widely used DFT codes, demonstrating that the precisionof DFT implementations can be determined, even in the absence of one absolute reference code.
Abstract: The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements.
1,141 citations
TL;DR: In this paper, the electronic and topological properties of alkaline-earth compounds were investigated based on first-principles calculations and an effective Hamiltonian analysis, and it was shown that when spin-orbit coupling is ignored, these materials are three-dimensional topological nodal-line semimetals characterized by a snakelike nodal loop in 3D momentum space.
Abstract: Based on first-principles calculations and an effective Hamiltonian analysis, we systematically investigate the electronic and topological properties of alkaline-earth compounds $A{X}_{2}$ $(A=\text{Ca}$, Sr, Ba; $X=\text{Si}$, Ge, Sn). Taking ${\mathrm{BaSn}}_{2}$ as an example, we find that when spin-orbit coupling is ignored, these materials are three-dimensional topological nodal-line semimetals characterized by a snakelike nodal loop in three-dimensional momentum space. Drumheadlike surface states emerge either inside or outside the loop circle on the (001) surface depending on surface termination, while complicated double-drumhead-like surface states appear on the (010) surface. When spin-orbit coupling is included, the nodal line is gapped and the system becomes a topological insulator with ${\mathbb{Z}}_{2}$ topological invariants (1;001). Since spin-orbit coupling effects are weak in light elements, the nodal-line semimetal phase is expected to be achievable in some alkaline-earth germanides and silicides.
192 citations
TL;DR: In this paper, the intrinsic electric field that exists in certain classes of materials plays a key role in many fields of electronics and the authors reveal and correct a shortcoming in the way that the electric polarization has been modeled in a technologically important class of these materials.
Abstract: The intrinsic electric field that exists in certain classes of materials plays a key role in many fields of electronics. Researchers reveal and correct a shortcoming in the way that the electric polarization has been modeled in a technologically important class of these materials.
76 citations
TL;DR: The results suggest that temperature-induced topological phase transitions should be observable near critical points of other external parameters.
Abstract: Calculations based on density-functional theory show that certain topological insulators can turn into conventional insulators at high temperature.
58 citations
TL;DR: An extremely rich physics strongly linked to ferroelectric properties, ranging from the electric control of bulk Rashba effect to the existence of a three-dimensional topological insulator phase, with concomitant topological surface states even in the ultrathin film limit is unveiled.
Abstract: By means of density functional theory based calculations, we study the role of spin-orbit coupling in the new family of $ABC$ hyperferroelectrics [Garrity, Rabe, and Vanderbilt Phys. Rev. Lett. 112, 127601 (2014)]. We unveil an extremely rich physics strongly linked to ferroelectric properties, ranging from the electric control of bulk Rashba effect to the existence of a three-dimensional topological insulator phase, with concomitant topological surface states even in the ultrathin film limit. Moreover, we predict that the topological transition, as induced by alloying, is followed by a Weyl semimetal phase of finite concentration extension, which is robust against disorder, putting forward hyperferroelectrics as promising candidates for spin-orbitronic applications.
47 citations
TL;DR: In this article, the authors present an extensive analysis of another promising family of ferroelectrics, the corundum derivatives $A\phantom{\rule{0}{0ex}}B\phantastic{O}_{3}$ and
Abstract: Perovskite and double perovskite oxides are perhaps the most studied ferroelectric and multiferroic materials. The authors present in this manuscript an extensive analysis of another promising family of ferroelectrics, the corundum derivatives $A\phantom{\rule{0}{0ex}}B\phantom{\rule{0}{0ex}}{O}_{3}$ and ${A}_{2}\phantom{\rule{0}{0ex}}B\phantom{\rule{0}{0ex}}{B}^{\ensuremath{'}}\phantom{\rule{0}{0ex}}{O}_{6}$. Despite a superficial similarity of the chemical formulas to single and double perovskites, the corundum derivatives have an entirely different structure and the mechanism for the polarization reversal. The authors perform a detailed first-principles study and arrive at empirical rules for evaluating the ferroelectric properties of materials in this class.
42 citations
TL;DR: The electronic structure of Ni_{3}TeO_{6} across the 53 K and 9 T magnetic transitions, both of which are accompanied by large changes in electric polarization, advances the understanding of magnetoelectric coupling in materials in which magnetic 3d centers coexist with nonmagnetic heavy chalcogenide cations.
Abstract: We combined high field optical spectroscopy and first principles calculations to analyze the electronic structure of ${\mathrm{Ni}}_{3}{\mathrm{TeO}}_{6}$ across the 53 K and 9 T magnetic transitions, both of which are accompanied by large changes in electric polarization. The color properties are sensitive to magnetic order due to field-induced changes in the crystal field environment, with those around Ni1 and Ni2 most affected. These findings advance the understanding of magnetoelectric coupling in materials in which magnetic $3d$ centers coexist with nonmagnetic heavy chalcogenide cations.
29 citations
TL;DR: In this article, optical absorption spectroscopy, photoconductivity, and first principles calculations were combined to reveal the electronic structure of the room temperature ferroelectric Ca3Ti2O7.
Abstract: We bring together optical absorption spectroscopy, photoconductivity, and first principles calculations to reveal the electronic structure of the room temperature ferroelectric Ca3Ti2O7. The 3.94 eV direct gap in Ca3Ti2O7 is charge transfer in nature and noticeably higher than that in CaTiO3 (3.4 eV), a finding that we attribute to dimensional confinement in the n = 2 member of the Ruddlesden-Popper series. While Sr substitution introduces disorder and broadens the gap edge slightly, oxygen deficiency reduces the gap to 3.7 eV and gives rise to a broad tail that persists to much lower energies.
29 citations
Journal Article•
TL;DR: In this article, the authors investigated a class of ABO3 and A2BB ′O6 materials that can be derived from the X2O3 corundum structure by mixing two or three ordered cations on the X site.
Abstract: The search for new ferroelectric (FE) materials holds promise for broadening our understanding of FE mechanisms and extending the range of application of FE materials. Here we investigate a class of ABO3 and A2BB ′O6 materials that can be derived from the X2O3 corundum structure by mixing two or three ordered cations on the X site. Most such corundum derivatives have a polar structure, but it is unclear whether the polarization is reversible, which is a requirement for a FE material. In this paper, we propose a method to study the FE reversal path of materials in the corundum derivative family. We first categorize the corundum derivatives into four classes and show that only two of these allow for the possibility of FE reversal. We then calculate the energy profile and energy barrier of the FE reversal path using first-principles density functional methods with a structural constraint. Furthermore, we identify several empirical measures that can provide a rule of thumb for estimating the energy barriers. Finally, the conditions under which the magnetic ordering is compatible with ferroelectricity are determined. These results lead us to predict several potentially new FE materials.
28 citations
TL;DR: It is found that the insulating ground state of a monolayer of La deposited on single-layer CrSiTe{3} (CrGeTe_{3}) carries spontaneously generated current loops around the Cr sites.
Abstract: We study adatom-covered single layers of ${\mathrm{CrSiTe}}_{3}$ and ${\mathrm{CrGeTe}}_{3}$ using first-principles calculations based on hybrid functionals. We find that the insulating ground state of a monolayer of La (Lu) deposited on single-layer ${\mathrm{CrSiTe}}_{3}$ (${\mathrm{CrGeTe}}_{3}$) carries spontaneously generated current loops around the Cr sites. These ``flux states'' induce antiferromagnetically ordered orbital moments on the Cr sites and are also associated with nontrivial topological properties. The calculated Chern numbers for these systems are predicted to be $\ifmmode\pm\else\textpm\fi{}1$ even in the absence of spin-orbit coupling, with sizable gaps on the order of 100 meV. The flux states and the associated topological phases result from spontaneous time-reversal symmetry breaking due to the presence of nonlocal Coulomb interactions.
26 citations
TL;DR: In this paper, a tunable inverse topological platform is proposed to tune the coupling between the TI layers from strongly coupled metallic to weakly coupled, and finally to a fully decoupled insulating regime.
Abstract: In typical topological insulator (TI) systems the TI is bordered by a non-TI insulator, and the surrounding conventional insulators, including vacuum, are not generally treated as part of the TI system. Here, we implement a material system where the roles are reversed, and the topological surface states form around the non-TI (instead of the TI) layers. This is realized by growing a layer of the tunable non-TI ${(\mathrm{B}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{I}{\mathrm{n}}_{x})}_{2}\mathrm{S}{\mathrm{e}}_{3}$ in between two layers of the TI $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ using the atomically precise molecular beam epitaxy technique. On this tunable inverse topological platform, we systematically vary the thickness and the composition of the ${(\mathrm{B}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{I}{\mathrm{n}}_{x})}_{2}\mathrm{S}{\mathrm{e}}_{3}$ layer and show that this tunes the coupling between the TI layers from strongly coupled metallic to weakly coupled, and finally to a fully decoupled insulating regime. This system can be used to probe the fundamental nature of coupling in TI materials and provides a tunable insulating layer for TI devices.
TL;DR: In this article, the authors decouple the simultaneous effects of temperature, stress, strain, and electric field on the optical phonon frequencies of gallium nitride (GaN) high electron mobility transistors (HEMTs).
Abstract: Due to the high dissipated power densities in gallium nitride (GaN) high electron mobility transistors (HEMTs), temperature measurement techniques with high spatial resolution, such as micro-Raman thermography, are critical for ensuring device reliability. However, accurately determining the temperature rise in the ON state of a transistor from shifts in the Raman peak positions requires careful decoupling of the simultaneous effects of temperature, stress, strain, and electric field on the optical phonon frequencies. Although it is well-known that the vertical electric field in the GaN epilayers can shift the Raman peak positions through the strain and/or stress induced by the inverse piezoelectric (IPE) effect, previous studies have not shown quantitative agreement between the strain and/or stress components derived from micro-Raman measurements and those predicted by electro-mechanical models. We attribute this discrepancy to the fact that previous studies have not considered the impact of the electric...