Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B31: Focus Session: Computational Discovery and Design of New Materials II |
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Sponsoring Units: DMP DCOMP Chair: Lin-Lin Wang, Iowa State University Room: 607 |
Monday, March 3, 2014 11:15AM - 11:51AM |
B31.00001: Associating Specific Materials with Topological Insulation Behavior Invited Speaker: Xiuwen Zhang The first-principles (a) total-energy/stability calculations combined with (b) electronic structure calculations of band inversion, spin-polarization and topological invariants (Z2) has led to the design and prediction of specific materials that are topological insulators in this study. We classify bulk materials into four types of band-inversion behaviors (TI-1, TI-2, BI-3, BI-4), based on the number of band inversions and their distributions on various time reversal invariant k points. Depending on the inversion type in bulk, the corresponding surface states have different protections e.g., protected by time reversal symmetry (in TI-1 materials), spatial symmetry (in TI-2), or not protected (in BI-3, BI-4). Subject 1 Discovery of new TI by screening materials for a Z2 metric: Such high-throughput search in the framework of Inverse Design methodology predicts a few previously undocumented materials that are TI-1 in their ground state crystal structure. We also predict dozens of materials that are TI-1 however in structures that are not ground states (e.g. perovskite structure of II-Bi-O3). Subject 2 Design Principle to increase the gap of TI-1 materials: In HgTe-like cubic topological materials, the insulating gap is zero since the spin-orbit splitting is positive and so a 4-fold half-filled p-like band is near the Fermi level. By design of hybridization of d-orbitals into the p-like bands, one can create negative spin-orbit splitting and so a finite insulating gap. Subject 3 Unconventional spin textures of TI surface states: Despite the fact that one of our predicted TI-1 KBaBi has inversion symmetry in the bulk--a fact that that would preclude bulk spin polarization--we find a Dresselhaus-like spin texture with non-helical spin texture. This originates from the local spin polarization, anchored on the atomic sites with inversion asymmetric point groups, that is compensated due to global inversion symmetry in bulk. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B31.00002: Determination of ground-state structure of perovskite super- lattices from first principles Yuanjun Zhou, Karin Rabe We propose an efficient method to find the ground state structure (GSS) of superlattices. It is based on the assumption that in the GSS of the superlattice, structures of the constituent layers will closely resemble a low-energy state of the pure compound at the relevant epitaxial strain. This method is especially suitable for high-throughput first-principles studies for the design of functional superlattices since the information about the low-energy states for a relatively small set of pure compounds, generated in a preprocessing step and stored in a database, can be used for the structure determination of a large space of constituent and layer thickness combinations. The method is demonstrated by application to the 2:2 PbTiO3/SrTiO3 superlattice. For tensile and compressive epitaxial strain, we find the GSS consistent with previous studies. For 0\% epitaxial strain, however, our method identifies two degenerate distinct ground-state structure candidates, only one of which was previously identified; further investigation confirms a complex energy landscape for this phase. Results for the Sr$M$O3/SrTiO3 series of superlattices, where $M$ = V, Cr, Co and Fe, will also be presented. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B31.00003: Ab initio search for new $p$-type transparent conductors among oxide sulfides Kanber Lam, Giancarlo Trimarchi, Arthur J. Freeman, Kenneth Poeppelmeier, Alex Zunger Optimal $p$-type, i.e., hole-conducting, transparent materials must meet the design metrics of large band gap for transparency, and light hole effective masses and large hole content for good $p$-type conductivity. The oxide sulfides could potentially satisfy these design metrics better than oxides do, owing to the stronger hybridization between the S $p$ and metal orbitals that can produce a more dispersive valence band maximum (VBM) and lighter hole masses than in oxides. LaOCuS is the prototype $p$-type transparent conductor (TC) among oxide sulfides. Here, we perform a density functional study of $\sim 30$ oxide sulfides, based on transition metals and column II and III elements, to identify compounds in this set that meet the design metrics for $p$-type TCs. We screen these materials using band gaps and hole effective masses. The analysis of the VBM wavefunctions shows that these oxide sulfides can be classified into ``band-mixed,'' with a continuous distribution of the wavefunction on both anions, and ``band-segregated,'' with the VBM mostly originating from one of the anions. The correlation between the type of VBM wavefunction and the O and S arrangement in the material (anion mixed vs. anion segregated) provides a designing criterion for new mixed-anion $p$-type TCs. [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B31.00004: First-principles data-driven discovery of new low-band-gap oxides for solar energy capture and conversion Qimin Yan, Wei Chen, Anubhav Jain, Kristin Persson, Jeffery B. Neaton We develop first-principles data driven discovery approach to explore experimentally-known oxide compounds with low band gaps. Cr-based oxide compounds comprise a nice test bed for assessing high throughput discovery of light absorbers and photocatalysts. An interesting subclass with promising band gaps, this Cr oxide testbed spans a range of electronic and magnetic properties; predicting trends across such a range can challenge for standard density functional theory and many-body perturbation theory. We focus on this set and implement a broadly-applicable high-throughput workflow for calculation of band gaps, adsorption spectra, and band edges, initially using semi-local and hybrid functionals. We develop best practices for analysis of these data, and successfully identify several promising new compounds for solar energy capture and conversion applications, which we then apply more rigorous many-body perturbation theory including GW method and beyond to further study their optical and electronic properties. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B31.00005: Origin of the large $p$-type conductivity in the misfit layered La$_5$Cu$_6$O$_4$S$_7$ oxide sulfide: a first-principles study Arthur J. Freeman, Jino Im, Kanber Lam, Giancarlo Trimarchi, Kenneth R. Poeppelmier Large $p$-type, i.e., hole, conductivity has been achieved only in very few transparent conducting oxides. Oxide sulfides can potentially display higher hole conductivity than oxides, due to the favorable hybridization between metal and sulfur orbitals at the valence band maximum. The layered oxide sulfide LaCuOS has been identified and extensively investigated as a $p$-type transparent conductor, yet its layered misfit analogue La$_5$Cu$_6$O$_4$S$_7$ was found to have an intrinsically larger hole conductivity and an optical gap of $\sim 2.0$ eV. We find through first-principles density-functional calculations that the S atoms in the chains embedded in the La-O layer in La$_5$Cu$_6$O$_4$S$_7$ can form S$_2$ dimers. Absence of dimers in the S chain results in a metallic band structure. This dimerization controls the opening of an optical gap. A random distribution of S$_2$ dimers together with isolated atoms along these S chains is a possible mechanism for the concurrent opening of an optical gap and the presence of a significant hole concentration in this material. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B31.00006: Structurally unstable III-Bi-O$_3$ perovskites are predicted to be topological insulators but their stable structural forms are just band insulators: A first principles study Giancarlo Trimarchi, Arthur J. Freeman, Xiuwen Zhang, Alex Zunger Several Bi oxides in the assumed cubic $Pm\bar{3}m$ perovskite structure have recently been identified as topological insulators or semi-metals by first-principles calculations. In these perovskites, Bi is at the octahedral site and the $A$ atom at the interstitial site is a column III cation, i.e., Al, Ga, In, Sc, Y, La. We use density functional total-energy calculations and crystal structure prediction to determine the energetically stable phases for these oxides. We find that these $Pm\bar{3}m$ $A$BiO$_{3}$ perovskites are topological insulators, confirming recent results obtained by our and other groups. However, switching the position of Bi and $A$ in the $Pm\bar{3}m$ perovskite produces trivial insulators or semimetals, as opposed to topological insulators. Indeed, symmetry-lowering via concerted tilting and internal deformation of the octahedra, stabilizes these Bi oxides, irrespective of the position of Bi, producing the stable $Pnma$ perovskite structure that is not a topological insulator. This illustrates that a simultaneous application of ``first-principles thermodynamics'' with first-principles electronic structure ($Z_{2}$ evaluation) is needed to establish stable topological insulators. [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B31.00007: A new class of polar mott-insulators via heterostructruring Chanul Kim, Hyowon Park, Chris Marianetti We propose simple design rules based on charge transfer and ion size to design a new class of polar Mott insulators in perovskite-based transition metal oxides. Ab Initio DFT+U calculations are then used to selectively scan phase space in double perovskites which have strong potential to be polar and Mott insulating. We begin by exploring pairs of A-type ions (A, A') and pairs of B-type ions (B, B') in $AA^{\prime}BB^{\prime}O_{6}$ which will have nominal charge transfer consistent with valencies that are conducive to a Mott insulator. Additionally, the A-type ions are chosen to have a large size mismatch and are ordered to break symmetry, creating conditions favorable to a polar distortion. We uncover a number of materials which are strong candidates to be polar Mott insulators in experiment, including BaLaVNiO$_{6}$, BaLaVCoO$_{6}$, BaLaVCuO$_{6}$, BaLaCrNiO$_{6}$, BaBiVCoO$_{6}$, BaBiVNiO$_{6}$, and PbLaVNiO$_{6}$. Furthermore, we show that the magnetic state and the band gap are sensitive to the particular ordering of the transition metals. Finally, we discuss possible applications and the potential to grow these systems in experiment. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B31.00008: Room-temperature quantum spin Hall effect in HgTe honeycomb superlattices Cristiane Morais Smith, Wouter Beugeling, Efterpi Kalesaki, Y.-M. Niquet, Christophe Delerue, Daniel Vanmaekelbergh The recent experimental realization of self-assembled honeycomb superlattices of truncated semiconducting nanocrystals has opened a new path to engineer graphene-like structures. Atomistic band-structure calculations for honeycomb lattices of PbSe and CdSe have shown a rich band structure, with Dirac cones at the $s$- as well as at the $p$-bands, in addition to a flat $p$-band. By controlling the chemical composition of the nanocrystals, lattices with strong spin-orbit coupling can be artificially designed. We show that for HgTe a huge non-trivial gap, of order of 50 meV, opens at the K-points. We calculate the edge states using both, an atomistic calculation that takes into account $10^6$ atomic orbitals per unit cell, as well as an effective 16-bands tight-binding model, and find that the quantum spin Hall effect should be observable in this material at temperatures of the order of room temperature. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B31.00009: Development of (MnO)$_{\mathrm{1-x}}$(ZnO)$_{\mathrm{x}}$ Alloys for Water Splitting Applications Paul Ndione, Emily Warren, Haowei Peng, Stephan Lany, David Ginley, Andriy Zakutayev Using high throughput combinatorial synthesis, measurement and analysis methodologies, we rapidly investigate the composition related structural, optical, and electrical properties of (MnO)$_{\mathrm{1-x}}$(ZnO)$_{\mathrm{x}}$ alloys and identify candidates materials for a more detailed study in PEC applications. The (MnO)$_{\mathrm{1-x}}$(ZnO)$_{\mathrm{x}}$ thin films are synthesized using combinatorial pulsed laser deposition with continuous orthogonal gradients in both chemical composition and substrate temperature. The solubility limit of ZnO into MnO is determined using the disappearing phase method and found to decrease with increasing temperature. For example, (MnO)$_{\mathrm{1-x}}$(ZnO)$_{\mathrm{x}}$ deposited at 300 C exhibit only the tetrahedral wurzite (WZ) structure instead of the rocksalt (RS) one at x\textgreater 0.4. Optical measurements indicate the strong reduction of the optical band gap associated with the RS to WZ transition, and are consistent with the first-principles theory prediction of E$_{\mathrm{gap}}=$2.1 eV at a x$=$0.5 alloy composition. The values of the electrical conductivity for the Ga-doped (MnO)$_{\mathrm{1-x}}$(ZnO)$_{\mathrm{x}}$ samples deposited at 300 C from a 4{\%} Ga-doped ZnO target are determined to be \textless 2 S/cm and 100 S/cm for the RS and WZ structure respectively per atom of Ga. These results suggest that Ga-doped MnO-ZnO alloys present a promising materials system for water oxidation in a PEC cell. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B31.00010: Prediction of novel, Earth abundant Cu2O based alloys for PV applications Vladan Stevanovic, Stephan Lany Tuning the opto-electronic properties of semiconductors through alloying is essential for semiconductor industry. Currently, mostly isovalent and isostructural alloys are used (e.g. Si/Ge, GaN/InN or CdTe/ZnTe), but a vast and unexplored space of novel functional materials is conceivable when considering more complex alloys by mixing aliovalent and heterostructural constituents. The real challenge lies in the quantitative property prediction for such complex alloys to guide their experimental exploration. In our work we demonstrate how an Earth abundant p-type oxide Cu2O, can be engineered through alloying into a technologically useful absorber material. We use non-local external potentials (NLEP) fitted to GW calculations for correcting the DFT electronic structure and compute absorption coefficient of different alloy compositions and configurations. [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B31.00011: Identifying Solid Sorbents for CO$_{2}$ Capture Technology by \textit{ab initio} Thermodynamic Approach Yuhua Duan Since the current technologies for capturing CO$_{2}$ are still too energy intensive, to develop new materials that can capture CO$_{2}$ reversibly with acceptable energy costs are needed. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO$_{2}$ sorbent candidates from the vast array of possible solid materials have been proposed and validated. The calculated thermodynamic properties of different classes of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for the CO$_{2}$ adsorption/desorption cycles. According to the requirements imposed by the pre- and post- combustion technologies and based on our calculated thermodynamic properties for the CO$_{2}$ capture reactions by the solids of interest, we were able to identify only those solid materials for which lower capture energy costs are expected at the desired pressure and temperature conditions. At a given CO$_{2}$ pressure, the turnover temperature (T$_{\mathrm{t}})$ of an individual solid capture CO$_{2}$ reaction is fixed. Such T$_{\mathrm{t}}$ may be outside the operating temperature range ($\Delta $T$_{\mathrm{o}})$ for a particularly capture technology. In order to adjust T$_{\mathrm{t}}$ to fit the practical $\Delta $T$_{\mathrm{o}}$, in this study, we demonstrate that by mixing different types of solids it's possible to shift T$_{\mathrm{t}}$ to the a range of practical operating temperature conditions. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B31.00012: First-principles design of organo-Sn polymeric dielectrics Huan Tran, Arun Kumar, Chenchen Wang, Aaron Baldwin, Rui Ma, Gregory Sotzing, Rampi Ramprasad Following on from recent computation-based suggestions that Sn-containing polymers may be promising dielectrics, one of them, poly (dimethyltin glutarate) (pDMTG), has been synthesized. The measured dielectric constant of pDMTG is $\epsilon \simeq 7.4$, significantly higher than the current standard material used for high-energy-density applications, namely, polypropylene ($\epsilon \simeq 2.2$). By performing first-principles calculations at the level of density functional theory and using the minima-hopping method to predict the stable structures (given that just the composition is provided), we propose four structural models of pDMTG. Based on these models, various physical properties of pDMTG, e.g., dielectric constant, infrared spectra and refractive index, are determined to closely agree with experimental data. The calculated band gap of pDMTG is high ($E_{\rm g} \simeq 6.1$ eV), implying that pDMTG is a promising candidate for high-energy-density materials. The strategy that has lead to the synthesis and understanding of pDMTG shows that density functional theory is a powerful method to study and design new materials. Our work is supported by the Office of Naval Research through the Multidisciplinary University Research Initiative (MURI). [Preview Abstract] |
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