Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M31: Focus Session: Computational Discovery and Design of New Materials IV |
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Sponsoring Units: DMP DCOMP Chair: Manh Cuong Nguyen, Ames Laboratory Room: 607 |
Wednesday, March 5, 2014 11:15AM - 11:51AM |
M31.00001: Design of Metamaterials for control of electromagnetic waves Invited Speaker: Thomas Koschny Metamaterials are artificial effective media supporting propagating waves that derive their properties form the average response of deliberately designed and arranged, usually resonant scatterers with structural length-scales much smaller than the wavelength inside the material. Electromagnetic metamaterials are the most important implementation of metamaterials, which are made from deeply sub-wavelength electric, magnetic and chiral resonators and can be designed to work from radio frequencies all the way to visible light. Metamaterials have been major new development in physics and materials science over the last decade and are still attracting more interest as they enable us to create materials with unique properties like negative refraction, flat and super lenses, impedance matching eliminating reflection, perfect absorbers, deeply sub-wavelength sized wave guides and cavities, tunability, enhanced non-linearity and gain, chirality and huge optical activity, control of Casimir forces, and spontaneous emission, etc. In this talk, I will discuss the design, numerical simulation, and mathematical modeling of metamaterials. I will survey the current state of the art and discuss challenges, possible solutions and perspectives. In particular, the problem of dissipative loss and their possible compensation by incorporating spatially distributed gain in metamaterials. If the gain sub-system is strongly coupled to the sub-wavelength resonators of the metamaterial loss compensation and undamping of the resonant response of the metamaterials can occur. I will explore new, alternative dielectric low loss resonators for metamaterials as well as the potential of new conducting materials such as Graphene to replace metals as the conducting material in resonant metamaterials. Two dimensional metamaterials or metasurfaces, implementations of effective electromagnetic current sheets in which both electric and magnetic sheet conductivities are controlled by the average response of sub-wavelength local resonators, emerge as simpler implementation of many of the unique properties of metamaterials. I will discuss a few novel examples how these metamaterials can be used for dispersion engineering, and beam shaping. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M31.00002: Computational nano-materials design of high efficiency photovoltaic materials by spinodal nano-decomposition in Chalcopyrite-type semiconductors Hideo Asahina, Yoshimasa Tani, Kazunori Sato, Hiroshi Katayama-Yoshida Chalcopyrite-type semiconductor CuInSe2 (CIS) is one of the most promising materials for low cost photovoltaic solar-cells due to its self-regeneration mechanism. However, from the point of resource security, high concentration of In in CIS is serious disadvantage. Recently, Cu2ZnSnS4 (CZTS) attracts much attention to overcome this disadvantage of CIS. This material has already been investigated as a photovoltaic material but the efficiency is not high enough. Based on the first-principles calculations by the KKR-CPA method, we propose how we can enhance the efficiency of CZTS by utilizing the self-organization phenomena caused by spinodal nano-decomposition of Cu \& Cu-vacancy, S \& Se, and Se \& Oxygen [1]. We will compare our design with the available experimental data of STEM-EDX, EELS, Atom Probe Tomography and Raman Scattering data. In addition to the above materials design, we also discuss intermediate band type solar-cells caused by the spinodal nano-decomposition, and propose Fe-doped CuFeS2-CuAlS2 (CFS-CAS), CuFeS2-CuGaS2 (CFS-CGS) and CuFeS2-CuInS2 (CFS-CIS) as promising materials with enhanced conversion efficiency up to 50\%.\\[4pt] [1] Y. Tani et al., Appl. Phys. Express 3 (2010) 101201. Jpn. J. Appl. Phys. 51 (2012) 050202. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M31.00003: Understanding Electronic, Optical and Thermal Properties of Transition Metal Chalcogenides (TMCs) Can Ataca, Rajamani Raghunathan, Sefaattin Tongay, Junqiao Wu, Jeffrey C. Grossman The fundamental properties of a material depend on their atomic structure, nature of bonding and elemental/chemical composition. Confinement of electrons in 2 dimensional planar structures leads to realization of several intriguing properties that are not seen in the bulk 3-dimendional counterparts. In this work, we explore the properties of single and few layer MX (M:Transition metal, X: chalcogen atom) both theoretically and experimentally. Using state of art density functional theory (DFT) we carried out a stability analysis through phonon and electronic, magnetic and elastic structure calculations where M$=$Cu, and X$=$S, Se, Te. The stacking of transition metal chalcogenide (TMC) monolayers is of the type MX-M2X2 instead of the usual X-M-X stacking found in TMDs. The differences in geometric structure result in many different stable monolayer forms with different electronic and magnetic properties. Depending on the number of layers, MX structures can be found in 2, 3, 4 and 6 MX layer stable configurations. These dimensionality effects predicted by DFT such as energy band structures and Raman active modes are confirmed by~experiments. Various different monolayers of MX possess a number of properties that make them highly promising materials for future nanoscale applications. [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M31.00004: Inverse Design of Materials by Multi-Objective Differential Evolution($IM^2ODE$) Yue-Yu Zhang, Z.L. Li, H.J. Xiang, X.G. Gong Inverse design is a new approach in the realm of material science for finding the structure with desired property. We developed a novel algorithm for inverse design named as $IM^{2}ODE$ (Inverse Design of Materials by Multi-Objective Differential Evolution). The target properties of concern include optical and electrical properties of semiconductors, solar absorbers and hardness of materials. $IM^{2}ODE$ can easily predict the atomic configurations with desired properties for crystal structures, interfaces and clusters. This novel method has been applied successfully in predicting new titanium dioxide ($\textrm{TiO}_2$) polymorph with optimal band gap for solar cell application. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M31.00005: Design of molecular sidechains to enhance thermal conductivity Kieran Mullen, Daniel Glatzhofer Higher thermal conductivity polymer composites would provide lighter and cheaper materials for large scale industrial applications as well as improve heat dissipation on the microscopic scale in electronics. Carbon nanotubes and graphene have high intrinsic thermal conductivity, but their large interface thermal resistance prevents their use in polymer composites. We investigate the design of molecular sidechains built from selectively chlorinated and/or fluorinated carbons which have the advantage of a higher linear mass density than an alkane chain and are expected to be quite stiff. We present results of a search for an optimal configuration of a sidechain consisting of a number of chlorinated carbon, fluorinated carbon, and simple hydrogenated carbon units that maximizes heat flow. This search will involve concepts from electron transport generalized to the study of phonon transport. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M31.00006: Efficiency enhancement due to self-organization of nano-structures in Cd(S, Te) solar cell material Kazunori Sato, Hiroshi Katayama-Yoshida CdTe is one of the most important solar cell materials. Its energy gap is 1.44 eV, which is ideal for solar cell application. So far, conversion efficiency of 18.3 percent has been realized, but it is lower than the Shockley-Queisser limit. In this paper, we propose computational materials design for enhancing conversion efficiency by using self-organization in Cd(Te, S) alloy semiconductor. Firstly, we performed cluster expansion of total energy of the Cd(Te, S) system and simulated self-organization of nano-structures in Cd(Te, S) by using Monte Carlo method. It is found that layered structure becomes stable by applying strain during the crystal growth. The electronic structure of the self-organized layered structure was calculated by using the hybrid method (HSE06) implemented in the VASP code to derive optical absorption coefficient. By using the calculated absorption coefficient the efficiency limit was derived based on the Shockley-Queisser theory. It is shown that the efficiency limit does not change so much due to the nano-structure formation. However, our calculation shows spatial separation between photo-generated electrons and holes. This might enhance the efficiency due to the suppression of recombination. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M31.00007: Is Orthorhombic C32 Actually a New Metastable Allotropic Form of Carbon? Taylor Just, Michael Mehl, Daniel Finkenstadt, Steven Richardson Carbon hybridizes in different geometries ($sp$, $sp^2$, and $sp^3$) forming a number of well-known allotropic forms such as: cubic diamond, graphite, $C_{60}$, graphene, hexagonal diamond, and amorphous carbon. With the advent of novel computational optimization tools many other candidate allotropic forms for carbon (e.g. monoclinic M-carbon, body-centered tetragonal C4 carbon (bct-C4), orthorhombic W-carbon, and Z-carbon) have been proposed which might be metastable at high pressures. In fact, the M-carbon structure has been experimentally seen with Raman spectroscopy. Recently, Zhang {\it et al.}\footnote{M. Zhang, H. Liu, Y. Du, X. Zhang, Y. Wang, and Q. Li, {\it Phys. Chem. Chem. Phys. {\bf15,}} 14120 (2013).} have reported the theoretical existence of a new allotropic form of carbon which they named: orthorhombic C32. In this work we have discovered that orthorhombic C32 is actually {\bf not} a novel carbon allotropic form of carbon, but it is simply hexagonal diamond decorated with defect planes separated by arbitrary distances. We have used first-principles DFT calculations to compute the energies and phonon spectra for these structures and compared our results with an extensive library of other possible metastable allotropic forms of carbon from the literature. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M31.00008: Ab-initio study of the electronic structure and optical properties for carbon in the glitter phase Juan Andres Diaz-Celaya, Eduardo Cifuentes-Quintal, Jose Luis Cabellos, Romeo de Coss Experimental evidence has showed the existence of a new crystalline phase of carbon. Electron diffraction studies show that this new phase of carbon has the same reflections that diamond but showing additional reflections that are forbidden for diamond. This new carbon has been called n-diamond. Although the results suggest that n-diamond correspond to a cubic phase, the crystal structure remains unclear. Thus, based on theoretical computational studies have been proposed different cubic structures to explain the observed diffraction patterns in n-diamond. However, recently has been proposed that the n-diamond could be explained by a tetragonal structure, which is called glitter. More recently, based on ab-initio calculations has been shown that the glitter structure is vibrationally stable. In this work, we study the electronic structure and optical properties of carbon in the glitter structure by means of first principles calculations. The electronic density of states of that carbon in glitter structure corresponds to a metallic material which is corroborating by the optical conductivity. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M31.00009: Atomic structures of magic ZnSe clusters from first principles calculation Sachin P. Nanavati, Shailaja Mahamuni, S.V. Ghaisas, Vijay Kumar We report the atomic and electronic structures of {\it magic} (ZnSe)$_n$ ($n$ = 13, 33, and 34) clusters, employing first principles technique based on a pseudopotential approach. These sizes are important as laser ablated plumes of ZnSe have clusters with ($n$) = 6, 13, 19, 23, \& 33 ZnSe molecular units in high abundance suggesting their high stablity and magic behavior. Earlier we had predicted the atomic structures of these clusters to be filled cage structures with a Se centered 3-D structure for $n$ = 13 and a cage/core structure for $n$ = 33 \& 34. In the later two cases, a core of Zn$_5$Se$_5$ and Zn$_6$Se$_6$, respectively, is enclosed by a Zn$_{28}$Se$_{28}$ cage to form a 3-D structure. In contrast to ZnSe clusters, ZnO clusters in this size range have empty cage structures. Therefore, we have performed further calculations using both, GGA-PBE and hybrid HSE06 type of exchange-correlation functionals that suggest that our conclusion for the size $n$ = 13 remains unchanged, but for larger clusters of sizes $n$ = 33 \& 34, hollow cage stuctures made up of 4- and 6-membered rings of ZnSe, are energetically more favourable than the filled cage structures. We shall discuss the trends in the electronic structure, binding enery, and HOMO-LUMO gap, as we vary the ZnSe size. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M31.00010: Prediction of elastic and vibrational stability for Sc, Ti, Y, Zr, Tc, Ru, Hf, Re, and Os in the fcc structure Romeo de Coss, Eduardo Cifuentes-Quintal, Aaron Aguayo, Gabriel Murrieta The discovery of a metastable phase for a given material is interesting because corresponds to a new bonding and new properties are expected. The calculation of the total-energy along the Bain path is frequently used as a method to find tetragonal metastable states. However, a local minimum in the tetragonal distortion is not a definitive proof of a metastable state, and the elastic and vibrational stability needs to be evaluated. In a previous work, using the elastic stability criteria for a cubic structure, we have shown that the transition metals with hcp ground state; Ti, Zr, and Hf have a fcc metastable phase. That result is interesting since the fcc crystal structure does not appear in the current pressure-temperature phase diagram of these metals, and support the experimental observations of fcc Ti and Zr in thin films. In the present work, we extend the stability study of the fcc structure to the non-magnetic transition metals with hcp ground state; Sc, Ti, Y, Zr, Tc, Ru, Hf, Re, and Os. We find that all the metals involved in this study have a metastable fcc structure, since the phonon band structure shows only positive frequencies. Finally, substrates on which the fcc structure of these metals could be growth epitaxially are predicted. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M31.00011: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M31.00012: Generalized Kanzaki-Krivoglaz model of lattice relaxations in concentrated size-mismatched substitutional alloys applied to Cu-Au and Fe-Pt systems Ivan Zhuravlev, Joonhee An, Kirill Belashchenko A generalization of the Kanzaki-Krivoglaz model to concentrated alloys was developed and applied to Cu$_{1-x}$Au$_x$ and Fe$_{1-x}$Pt$_x$ alloys at x = 0.25, 0.5, and 0.75. This model is based on many-body cluster expansions of the configuration-dependent Kanzaki forces and force constants defined with respect to the ideal fcc lattice. The parameters of these expansions were directly fitted to the forces calculated from first-principles for a number of ordered structures at fixed concentration and volume. The Kanzaki forces are dominated by nearest-neighbor terms, which are strongly asymmetric between the atomic species. This asymmetry leads to a non-pairwise effective interaction with a long-range elastic singularity. The ability to capture this singular non-pairwise interaction accurately is a major advantage of the generalized Kanzaki-Krivoglaz model. The comparison of the predicted stable phases and ordering temperatures with experiment is generally favorable; while the prediction for Cu$_{0.25}$Au$_{0.75}$ is wrong due to a known failure of semi-local functionals, the remaining discrepancies for Cu$_{0.5}$Au$_{0.5}$ and Fe$_{0.25}$Pt$_{0.75}$ are attributed to the contributions from the strong tetragonal striction in the L1$_0$ phase and of magnetic disorder, respectively. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M31.00013: On relationship among composition, electronic structure and reactivity of catalytically active monolayers on metal substrates Sergey Stolbov, Sebastian Zuluaga Rational design of efficient electrocatalysts requires understanding of the relationship among the surface composition, its electronic structure, reactivity and catalytic activity. In this work by applying the first principle computational approach, we reveal the nature of the substrate effects on the electronic structure and reactivity of active monolayers (AM) deposited on a metal substrate (MS). In particular, we consider the Pt/MS structures (MS$=$Au, Ir, Ru, or Pt substrate). We reveal rationale for the interlayer hybridization to dominate over the strain effect in determining the AE/MS surface reactivity, in contrast to a widely accepted opinion that a strain is the main factor controlling the reactivity. We also find that, if AE is weakly bound to MS, the surface electronic structure does not suffice to characterize the surface reactivity, because of involvement of lattice response to adsorption of a reaction intermediate. We trace surface reactivity to a newly introduced hybridization parameter that reflects important features of the electronic structure of the AE/MS surface, which are not taken into account in the original $d-$band center model. [Preview Abstract] |
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