Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S32: Computational Discovery and Design of Novel Materials XFocus
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Sponsoring Units: DMP DCOMP Chair: Anton van der Ven, UCSB Room: 295 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S32.00001: Predicting giant caloric effects in selected magnetic and shape-memory alloys. Nikolai Zarkevich, Durga Paudyal, Duane Johnson We investigate giant caloric effect in selected classes of materials, detailing entropy contributions during phase transformations. Our target material is environmentally friendly and commercially viable with a reversible transformation having a small hysteresis and a large temperature change $\Delta $T at practical applied fields. Given that hysteresis widths increase with height of enthalpy barriers, and that large entropy change at a finite heat capacity yields a large $\Delta $T during the phase change, we may screen for promising candidates for caloric heating or cooling. FeRh is a showcase for caloric materials genome, transforming upon heating from type-2 antiferromagnet (AFM) to ferromagnet (FM). Its AFM (but not FM) B2 lattice has instabilities, which enlarge the entropy. Detailing caloric origin provides guidance to predict new materials and tune properties, as with doped Fe-Mn, LaFe$_{\mathrm{13}}$, and Ni-Ti, for optimal performance in practical applications. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S32.00002: Ab-Initio Insights into Novel Magnetic Behavior in the Mn$_{1-x}$Fe$_x$Ru$_2$Sn Pseudo-Binary Heusler Elizabeth Decolvenaere, Michael Gordon, Ram Seshadri, Anton Van der Ven Many Heusler compounds possess magnetic properties well-suited for applications as spintronic materials. The pseudo-binary Mn$_{0.}5$Fe$_{0.5}$Ru$_2$Sn, formed as a solid solution of two full Heuslers, has been recently shown to exhibit exchange-hardening suggestive of two \textit{magnetic} phases, despite only one observed \textit{chemical} phase[1]. We have performed ab-initio studies of over one hundred chemical and magnetic orderings of the Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn pseudo-binary to better understand the unique magnetic behavior developing in this system. Utilizing a mixed-basis chemical-and-magnetic cluster expansion, we find a transition from ferromagnetic (FM) to antiferromagnetic (AFM) behavior dependent on composition, with (111) AFM ordering on the Mn species at equiatomic composition, in agreement with the experimental study. By exploring and examining the ensemble-averaged magnetic and chemical configurations at multiple compositions and temperatures, we identify the mechanism behind the apparent magnetic hardening, driven by alternating planes of FM and AFM-ordered spins at equiatomic and iron-rich compositions. [1] J. Douglas, E. Levin, T. Pollock. J. Castillo, P. Adler, C. Felser, S. Kr{\"a}mer, K. L. Page, R. Seshadri. Phys. Rev. B 94, 094412 (2016) [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S32.00003: First-principles prediction of a stable hexagonal phase of CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ Arashdeep Thind, Xing Huang, Rohan Mishra Methylammonium lead iodide (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ or MAPbI$_{\mathrm{3}})$ is a promising photovoltaic material with high power conversion efficiency. However, its experimental perovskite phases show poor thermodynamic stability. Using first-principles density functional theory, we predict a hexagonal (\textit{2H}) phase with $P63mc$ space-group symmetry to be the thermodynamically most stable phase. The \textit{2H}-phase consists of infinite chains of face-shared PbI$_{\mathrm{6}}$ octahedra with organic MA cations taking up the space between the chains, which is in contrast to the corner-connected octahedra observed in the experimental orthorhombic, tetragonal, and cubic phases. It has a negative formation enthalpy, independent of the choice of exchange correlation functional used in the calculations. The absence of soft-phonon modes in the \textit{2H}-phase demonstrates its dynamical stability. The \textit{2H}-phase has an indirect band gap of 2.6 eV, which is \textasciitilde 1 eV larger than the direct band gap of orthorhombic phase. The change in octahedral connectivity favors strongly anisotropic charge transport. Overall, the \textit{2H}-phase presents a new route to overcome the stability issues in MAPbI$_{\mathrm{3}}$. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S32.00004: Electronic and Magnetic Properties of Ba, Ni and BaNiO$_{3}$: A First-Principles Study Rupesh Ghimire, Narayan Adhikari, Gopi Kaphle, Ramesh Mani The electronic and magnetic Properties of Ba, Ni and hexagonal crystal structure BaNiO$_{3\, }$have been studied under TB-LMTO ASA method. The space group of compound is P6$_{3}$/mmc and lattice parameters are a$=$b$=$5.62 A$^{^{\circ}\, }$and c$=$4.81 A$^{^{\circ}}$. From our calculation, the minimized lattice parameters of Ba, Ni and BaNiO$_{3\, }$were found to be 5.280 A$^{^{\circ}}$, 3.488 A$^{^{\circ}\, }$and 6.08 A$^{^{\circ}}$ which are at most 1{\%} deviation from the experimental values. Band Structures were determined using the minimized structures which showed the metallic nature of elements Ba and Ni. However, the compound BaNiO$_{3\, \, }$possessed a band gap of 0.95 eV under LDA calculation. Further, U correction was implemented to account for the orbital dependent potential arising largely from the strong correlation of d and f electrons, and the band gap increased to 1.59 eV which is close to the theoretically expected gap ( 1.612 eV ). Density of states showed the ferromagnetic nature of the element nickel with a magnetic moment of 0.59$\mu_{B}_{\, }$close to that of experimental 0.60$\mu_{B}_{,}$ whereas the compound BaNiO$_{3\, \, }$itself was non-magnetic. Finally, a brief study of the charge properties showed the presence of ionic and covalent bonds between the atoms. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S32.00005: Controlling Elastic Properties in Perovskites with Polyhedral Connectivity Nicholas Wagner, James Rondinelli Using density functional theory, we investigate the effect of $B$O$_6$ octahedral face-sharing on the macroscopic mechanical properties of $AB$O$_3$ compounds ($A$=Sr, Ba) ($B$= Ti, Mn, Ni, Zr). We consider four structure prototypes of which three are hexagonal perovskites, exhibiting different ratios of corner-connected octahedra to face-connected octahedra (33\%, 50\%, \& 100\%). The fourth structure, cubic perovskite, exclusively exhibits corner-connected octahedra. We find that increasing the proportion of face-sharing to corner-sharing results in a decrease in the elastic constants independent of the $d$ orbital filling or cation size. Next, we explore the role of local and crystal structure features on this trend with a random forest regression model to identify that the volume per atom and trigonal distortion amplitude may serve as useful descriptors to predict this decrease. Finally, we propose how changing this trigonal distortion can potentially be used to engineer electronic properties such as the bandgap in these materials. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:51PM |
S32.00006: Making machine learning interatomic potentials accurate, efficient, and reliable Invited Speaker: Alexander Shapeev Molecular modeling relies, typically, on two classes of models of interatomic interaction, namely (1) quantum-mechanical (QM) models that are very accurate but very computationally expensive, and (2) empirical interatomic potentials that typically offer only a qualitative accuracy but are very computationally efficient. There have been a number of successful applications of machine learning to constructing interatomic potentials that combine the efficiency of empirical potentials and the accuracy of QM models [Behler and Parrinello, PRL (2007), Bartok et al., PRL (2010)]. A harder challenge, however, is to make such potentials reliable - it requires fitting hundreds to thousands of parameters and making sure that they produce reasonable results in the entire region of interest in the phase space (which could be given only implicitly, e.g., all configurations with energy below a certain threshold).\\ \\In my talk I will give a mathematician's perspective on the field of machine learning interatomic potentials. I will then present an example of accurate and computationally efficient machine learning interatomic potentials, and finally I will show how active learning can ensure reliability of such potentials. I will illustrate applications of such potentials in molecular dynamics and crystal structure prediction. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S32.00007: Effective Hamiltonians to Describe Octahedral Tilt Instabilities in Halide Perovskites Jonathon Bechtel, John Thomas, Anton Van der Ven Configurational cluster expansions, based on discrete occupation variables, have proven invaluable for constructing finite-temperature phase diagrams. Here, we develop a cluster expansion method to include continuous degrees of freedom. In this way we capture the effects of anharmonic interactions and high-temperature dynamic instabilities which are needed to describe structural phase transitions as a function of temperature. As a polynomial parameterization of the quantum mechanical zero Kelvin energy surface, the described effective Hamiltonians link \textit{ab initio }calculations to finite-temperature thermodynamics through Monte Carlo simulations. We present the methodology and apply it in a study of phase transitions in perovskite systems where symmetry breaking occurs through octahedral tilts. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S32.00008: ABO3 perovskite topological insulators: the enabling electronic motif and its structural stability Xiuwen Zhang, Leonardo Abdalla, Qihang Liu, Alex Zunger Oxide topological insulators (TI's) that could bring together the traditional oxide functionalities with the band topology of TI's have been sought for years. Here, we identify the electronic and structural motif (`topological gene') that achieves a topological band inversion in oxide perovskite as being a lone-pair B atom at the octahedral site in the cubic ABO3. However, at ambient pressure, the crystal structures that harbor the topological gene tend to develop an energy lowering distortion that removes the topological band inversion. We use this understanding to identify the `window of opportunity' where TI-ness and stability can coexist: at moderate pressures the TI phases can be stabilized, bringing the `topological gene' into coincidence with the `stability gene'. This illustrates the fact that TI-ness and stability are sometimes contraindicated, and traces the approach that will be needed to establish their coexistence, tunable by external pressure. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S32.00009: First-principles predictions of perovskite-type alkali metal titanium oxyhydrides with two-dimensional electronic states Nobuya Sato, Ryosuke Akashi, Shinji Tsuneyuki The electric properties of perovskite-type oxides $AB\mathrm{O}_3$ can be controlled by substituting $A$ and $B$ cations, while their chemical compositions are limited by the charge neutrality, e.g., $A^{2+}B^{4+}\mathrm{O}^{2-}_3$. A way of realizing other compositions is substitution of oxygen atoms with monovalent anions, e.g., $A^+B^{4+}\mathrm{O}^{2-}_2X^-$. Such substitution has been recently realized in experiments with fluorine atoms\footnote{T. Katsumata et al., J. Appl. Phys. 104, 044101 (2008).}, and more recently, with hydrogen\footnote{Y. Kobayashi \textit{et al}., Nature Mater. \textbf{11}, 507 (2012)}. Since the valence orbital character of hydrogen atoms ($s$) is different from that of oxygen and fluorine atoms ($p$), oxyhydrides should exhibit interesting electronic properties. In this study, we explore the property of unsynthesized oxyhydrides $A\mathrm{TiO}_2\mathrm{H}$ for alkali metals $A$ by first-principles calculations\footnote{For $A = \mathrm{K}$, N. Sato and S. Tsuneyuki, Appl. Phys. Lett. \textbf{109}, 172903 (2016).}. For $A = \mathrm{K}$, $\mathrm{Rb}$, $\mathrm{Cs}$, two-dimensional electronic states emerge at the valence band maximum, which has $\mathrm{H}$ $1s$ characteristics. Their dielectric and piezoelectric properties are also discussed. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S32.00010: First-principles Study of Phonons in Structural Phase Change of Ge-Sb-Te Compounds Young-Sun Song, Jeongwoo Kim, Minjae Kim, Seung-Hoon Jhi Ge-Sb-Te (GST) compounds, exhibiting substantial electrical and optical contrast at extremely fast switching modes, have attracted great attention for application as non-volatile memory devices. Despite extensive studies of GST compounds, the underlying mechanism for fast transitions between amorphous and crystalline phases is yet to be revealed. We study the vibrational property of various GST compounds and the role of nitrogen doping on phase-change processes using first-principles calculations. We find that a certain vibrational mode (Eu) plays a crucial role to determine transition temperatures, and that its frequency depends on the amount of Ge in GST. We also find that the nitrogen doping drives crystalline-amorphous transition at low power consumption modes. In addition, we discuss the effect of the spin-orbit coupling on vibration modes, which is known essential for correct description of the electrical property of GST. Our understanding of phonon modes in GST compounds paves the way for the improving the device performance especially in terms of switching speed and operating voltage. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S32.00011: Tin sulfides and tin selenides at ambient and high pressure conditions Kien Nguyen Cong, Joseph Gonzalez, Brad Steele, Ivan Oleynik The application of high pressure promotes unusual chemical bonding in condensed phase resulting in the synthesis of novel materials, which may be recoverable in metastable states at ambient conditions. First-principles evolutionary crystal structure search is performed to explore novel tin sulfide (Sn$_{\mathrm{x}}$S$_{\mathrm{y}})$ and tin selenide (Sn$_{\mathrm{x}}$S$_{\mathrm{y}})$ crystals with the goal to discover novel photovoltaic and thermoelectric materials. Variable stoichiometry searches at various pressures are performed and the phase diagrams are constructed in the range of pressures 0-100 GPa, which include both the thermodynamically stable and lowest enthalpy metastable structures. Several new structures are identified and their dynamical stability is investigated. To help experimental synthesis of these novel compounds, Raman spectra and XRD patterns are also calculated. These new materials are also investigated to identify those with promising photovoltaic and thermoelectric properties. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S32.00012: High-pressure intermetallic compounds and their properties in ambient-immiscible systems Maximilian Amsler, Shahab Naghavi, Chris Wolverton High-pressure synthesis has recently proven to be a promising approach for the discovery of novel compounds with exciting properties that do not exist at ambient conditions. In the majority of high-pressure studies the precursors placed in a diamond anvil cell already contain constituent elements that are known to form compounds at some condition since this is the most promising approach to avoid elemental decomposition. This common practice however limits the combinations of starting elements considered, and hence a vast chemical space remains completely unexplored at high pressure. In contrast, studying alloy systems at high pressures with severe immiscibility at ambient conditions (i.e. not forming compounds or exhibiting mutual solubility over any composition-temperature-range) is a difficult endeavor. These ``ambient-immiscible'' systems pose a significant materials discovery challenge since no information is available if and when inter atomic bonds will form, and what crystal structures potential compounds might have once the constituent elements are exposed to pressure. We will present the discovery of high-pressure intermetallics in bismuth-containing, ambient-immiscible binary systems and their properties using structural search and ab initio calculations. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S32.00013: High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Perovskite Oxide Heterostructures. Kesong Yang, Safdar Nazir, Mazir Behtash, Jianli Cheng The perovskite-based oxide heterointerfaces between two wide-band-gap insulators such as LaAlO$_{\mathrm{3}}$ and SrTiO$_{\mathrm{3}}$ are attracting increasing interests because of their novel electronic properties such as the two-dimensional electron gas (2DEG) at the interface that have potential applications in the next-generation nanoelectronic devices. In this talk, we show that a group of combinatorial descriptors such as the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the SrTiO$_{\mathrm{3}}$ substrate, can be introduced to realize a high-throughput (HT) design of SrTiO$_{\mathrm{3}}$-based 2DEG systems using perovskite-oxide-oriented quantum materials database. By using these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. 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. [Preview Abstract] |
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