Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C5: Focus Session: Computational Discovery and Design of New Materials for Energy Applications |
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Sponsoring Units: DMP DCOMP Chair: Richard Hennig, Cornell University Room: 301 |
Monday, March 18, 2013 2:30PM - 3:06PM |
C5.00001: Computational materials design for energy applications Invited Speaker: Vidvuds Ozolins General adoption of sustainable energy technologies depends on the discovery and development of new high-performance materials. For instance, waste heat recovery and electricity generation via the solar thermal route require bulk thermoelectrics with a high figure of merit ($ZT$) and thermal stability at high-temperatures. Energy recovery applications (e.g., regenerative braking) call for the development of rapidly chargeable systems for electrical energy storage, such as electrochemical supercapacitors. Similarly, use of hydrogen as vehicular fuel depends on the ability to store hydrogen at high volumetric and gravimetric densities, as well as on the ability to extract it at ambient temperatures at sufficiently rapid rates. We will discuss how first-principles computational methods based on quantum mechanics and statistical physics can drive the understanding, improvement and prediction of new energy materials. We will cover prediction and experimental verification of new earth-abundant thermoelectrics, transition metal oxides for electrochemical supercapacitors, and kinetics of mass transport in complex metal hydrides. [Preview Abstract] |
Monday, March 18, 2013 3:06PM - 3:18PM |
C5.00002: Design and synthesis of a crystalline LiPON electrolyte N.A.W. Holzwarth, Keerthi Senevirathne, Cynthia S. Day, Abdessadek Lachgar, Michael D. Gross In the course of a computation study of the broad class of lithium phosphorus oxy-nitride materials of interest for solid electrolyte applications, Du and Holzwarth,{\footnote{Y. A. Du and N. A. W. Holzwarth, {\em{Phys. Rev. B}} {\bf{81}} 184106 (2010)}} recently predicted a stable crystalline material with the stoichiometry Li$_2$PO$_2$N. The present paper reports the experimental preparation of the material using high temperature solid state synthesis and reports the results of experimental and calculational characterization studies. The so-named $SD$-Li$_2$PO$_2$N crystal structure has the orthorhombic space group $Cmc2_1$ with lattice constants a=9.0692(4) \AA, b=5.3999(2) \AA, and c=4.6856(2) \AA. The structure is similar but not identical to the predicted structure, characterized by parallel arrangements of anionic phosphorus oxy-nitride chains having planar P$-$N$-$P$-$N backbones. Nitrogen 2p$\pi$ states contribute to the strong bonding and to the chemical and thermal stablility of the material in air up to 600$^{\circ}$ C and in vacuum up to 1050$^{\circ}$ C. The measured Arrhenius activation energy for ionic conductivity is 0.6 eV which is comparable to computed vacancy migration energies in the presence of a significant population of Li$^{+}$ ion vacancies. [Preview Abstract] |
Monday, March 18, 2013 3:18PM - 3:30PM |
C5.00003: Proton Diffusion Model for High-Throughput Calculations Pandu Wisesa, Tim Mueller Solid oxide fuel cells (SOFCs) have many advantages over other fuel cells with high efficiency, myriad fuel choices, and low cost. The main issue however is the high operating temperature of SOFCs, which can be lowered by using an electrolyte material with high ionic conductivity, such as proton conducting oxides. Our goal is to identify promising proton-conducting materials in a manner that is time and cost efficient through the utilization of high-throughput calculations. We present a model for proton diffusion developed using machine learning techniques with training data that consists of density functional theory (DFT) calculations on various metal oxides. The built model is tested against other DFT results to see how it performs. The results of the DFT calculations and how the model fares are discussed, with focus on hydrogen diffusion pathways inside the bulk material. [Preview Abstract] |
Monday, March 18, 2013 3:30PM - 3:42PM |
C5.00004: Atomistic level description of phase diagram of gas clathrate hydrates with complex gas compositions R. Belosludov, H. Mizuseki, Y. Kawazoe, O. Subbotin, V. Belosludov An approach has been realized that allows us to construct a p-T phase diagrams of various gas hydrates, three-dimensional hydrogen-bonded water structures in which water molecules arrange themselves in a cage-like (host) structure around gas (guest) molecules, with complex gas compositions [1-2]. In order to evaluate the parameters of weak interactions, a TDDFT formalism and LDA technique entirely in real space have been implemented for calculations of vdW dispersion coefficients for atoms within the all-electron mixed-basis approach. The combination of both methods enables one to calculate thermodynamic properties of clathrate hydrates without resorting to any empirical parameter fittings. Using the proposed method it is possible not only confirm the existing experimental data but also predict the unknown region of thermodynamic stability of clathrate hydrates, and also propose the gas storage ability as well as the gas composition for which high-stability region of clathrate hydrates can be achieved. The proposed method is quite general and can be applied to the various non-stoichiometric inclusion compounds with weak guest-host interactions.\\[4pt] [1] R. V. Belosludov et al. J. Chem Phys. 131 (2009) 244510\\[0pt] [2] R. V. Belosludov et al. Mol. Simul. 38 (2012) 773. [Preview Abstract] |
Monday, March 18, 2013 3:42PM - 4:18PM |
C5.00005: Materials for Alternative Energies: Computational Materials Discovery and Crystal Structure Prediction Invited Speaker: Chris Wolverton Many of the key technological problems associated with alternative energies may be traced back to the lack of suitable materials. The materials discovery process may be greatly aided by the use of computational methods, particular those atomistic methods based on density functional theory. In this talk, we present an overview of recent work on energy-related materials from density-functional based approaches. We have developed novel computational tools which enable accurate prediction of crystal structures for new materials (using both Monte Carlo and Genetic Algorithm based approaches), materials discovery via high-throughput, data mining techniques, and automated phase diagram calculations. We highlight applications in the area of Li battery materials and hydrogen storage materials. [Preview Abstract] |
Monday, March 18, 2013 4:18PM - 4:30PM |
C5.00006: Multigap Semiconducting ferroelectric perovskites Lai Jiang, Ilya Grinberg, Fenggong Wang, Peter Davies, Andrew Rappe The energy conversion efficiency of a solar cell is directly related to the band gap of the material. By doping ferroelectric perovskites with Bi$^{5+}$ on the $B$-site, we propose low band-gap materials suitable for bulk photovoltaic effect and related solar applications.Our DFT calculations indicate that the low-lying 6$s$ empty states of the electronegative Bi atom produce empty isolated bands in the gap of the parent materials, effectively lowering the band gap by 1$\sim$2eV in various perovskites. Ferroelectricity (and therefore inversion symmetry breaking) weakens but survives upon doping, which enables the ``shift current'' mechanism for photocurrent generation, while the decreased band gap helps absorb low energy photons in the visible range. Furthermore, the existence of multiple band gaps allows for solar conversion devices with efficiency beyond the traditional Shockly-Queisser limit, in which successive photon excitations result in carriers with higher energy than a single-step excitation would achieve. [Preview Abstract] |
Monday, March 18, 2013 4:30PM - 4:42PM |
C5.00007: Search for highly absorbing thin-film photovoltaic absorbers in the system Cu-V-VI from first principles calculations Liping Yu, Robert S. Kokenyesi, Douglas A. Keszler, Alex Zunger To enable high-efficiency solar conversion, thin-film absorbers need to have strong absorption of photons across the solar spectrum. While the CuInSe$_2$-like materials have strong absorption, their measured rise in absorption near the band gap necessitates the use of rather thick films. This thickness, coupled with the relatively low abundance of In, potentially limits the scalability of this technology to the terawatt scale. Here we screen and assess absorption properties of $\sim$40 earth-abundant Cu-V-VI (V = P,As,Sb,Bi) materials, based on the recently proposed selection metric of ``Spectroscopic Limited Maximum Efficiency'' (SLME) [PRL. 108, 068701 (2012)]. This metric depends explicitly on calculated absorption spectra and accounts for different types of optical transitions near the absorption threshold. According to the SLME values calculated from 1st-principles quasiparticle GW theory, we propose five Cu-V-VI candidate thin-film absorber materials that have optical absorption stronger than CuInSe$_2$, which can be ascribed to the enhancement of the density of states near the conduction band maximum. The finding leads to refined design principles in support of the continuing quest for optimal absorber materials. [Preview Abstract] |
Monday, March 18, 2013 4:42PM - 4:54PM |
C5.00008: Accurate surface ionization potentials and electron affinities of semiconductors and insulators, a step toward water splitting predictions Vladan Stevanovic, Stephan Lany, Alex Zunger Design of semiconductors for water splitting requires knowledge of the position of band edges relative to the water redox potential. This can be achieved by predicting materials' ionization potentials (IPs) and electron affinities (EAs). We recently developed a predictive method combining different electronic structure techniques, which is able, as will be demonstrated, to reproduce IPs and EAs of a broad range of materials including standard semiconductors (GaAs, ZnO, CdS,\dots) and transition metal compounds (TiO2, MnO,\dots). Achieved accuracy is within 0.1-0.2 eV from the measured photoemission data. We use GGA(+U) to calculate the electronic structure of bulk systems and their surfaces leading to the alignment of the bulk GGA(+U) band edges with the vacuum. The many-body, quasiparticle GW method is used to calculate shifts of the bulk band edges with respect to the underlying GGA(+U) formalism. Combining GGA(+U) and GW results in accurate IPs and EAs. In the case of transition metal compounds additional external d-potentials are included in the selfconsistent GW cycle to account for the inaccurate position of the transition metal d-orbitals relative to s and p-orbitals, leading to accurate IPs and EAs also in these, for the electronic structure methods problematic, cases. [Preview Abstract] |
Monday, March 18, 2013 4:54PM - 5:06PM |
C5.00009: First principle studies of doping effects on the electronic and geometric structures of graphitic C3N4 Sebastian Zuluaga, Sergey Stolbov Layered carbon nitride g-C3N4 is a promising material as a photo-anode for the H production from water. By doping, the band gap (2.7 eV) can be tuned to the value optimal for efficient absorption of visible light irradiation. We present here our first principle computational study of the effects of doping with B, P and S on the geometric and electronic structures of g-C3N4 and compare them to experimental results. We have evaluated within density functional theory the energetics of various doping scenarios in terms of both thermodynamics and kinetics, and selected the energetically most favorable structures. Our calculations reveal important details of valence charge density redistribution upon the doping. The doping effect on the electronic density of states (DOS), in particular on band gap width, has been evaluated using an accurate GW method. We find the DOS to strongly depend on the doping geometry. The detailed analysis of the projected DOS provides significant insight into the mechanism underlying modification of the electronic structure upon doping. [Preview Abstract] |
Monday, March 18, 2013 5:06PM - 5:18PM |
C5.00010: Stabilizing and enhancing activity of Ag as a catalyst for oxygen redaction reaction on hydrogen fuel cell cathodes Sergey Stolbov, Marisol Alcantara Ortigoza Progress in searching for cost-effective and highly active catalysts for the oxygen reduction reaction (ORR) on hydrogen fuel cell cathodes is hindered by the fact that only a few elements (expensive and scarce Pt, Ir, Au) do not dissolve in the reaction environment (acidic medium at the expected operating potential $+$0.8 to $+$1.0 V vs SHE). Yet, in this work, we explore silver as an active element for the ORR catalysts. Although the dissolution potential (DP) of elemental Ag is 0.8 V, we rely on our finding [1] that binding of a metal monolayer (ML) to a reactive substrate can significantly increase its DP. Using our approach [1], we select Ag/Ru/W, Ag/Nb, and Ag/Ta as promising candidates for the ORR catalysts (where Ag and Ru are MLs). Our evaluation of DP within density functional theory (DFT) shows that, indeed, in the selected structures, DP of Ag significantly increases as compared to that of Ag(111) and, in the case of Ag/Nb, even exceeds that of Pt. The ORR free-energy diagrams calculated within DFT suggest that the above systems are more active toward ORR than Pt. We thus predict here three highly active and truly cost-effective ORR catalysts. [1] S. Stolbov, M. Alcantara Ortigoza, J. Phys. Chem. Letts. 3, 463 (2012). [Preview Abstract] |
Monday, March 18, 2013 5:18PM - 5:30PM |
C5.00011: Two dimensional N-containing carbon materials for oxygen reduction reaction Yexin Feng, Zhenpeng Hu, Lixin Zhang Seeking Pt replacement catalysts for cathode oxygen reduction reaction (ORR) is very important for the application of some new energy technologies like fuel cells and lithium-air batteries. N-doped graphene and carbon nitride sheets are two kinds of promising materials. For the N-doped graphene, it is found that nitrogen clusters other than isolated substitutionals are the active sites for oxygen reduction. Clusters with three or four N atoms are found to be the most active. Codoping boron (or Fe, Co) can effectively stabilize these high energy clusters while keep the cluster's high activity. For the carbon nitride sheets, in the C:N ratio range of 2.0-3.0, they are stable enough and can potentially catalyze the oxygen reduction as efficiently as Pt. It is revealed that the concentration of nitrogen can tune the Fermi level of the material and thus the catalytic property. The catalytic sites are located at those carbon atoms with special configurations rather than the nitrogen atoms. These results are helpful in designing N-containing carbon materials for ORR. [Preview Abstract] |
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