Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V6: Hybrid Functionals Applied to Solids |
Hide Abstracts |
Sponsoring Units: DCOMP Chair: Chris Van de Walle, University of California, Santa Barbara Room: Ballroom C2 |
Thursday, March 24, 2011 8:00AM - 8:36AM |
V6.00001: The shortcomings and advantages of hybrid functionals in the description of solids Invited Speaker: For extended systems, density functional theory currently possesses the optimal balance between computational efficiency and accuracy. Hence its wide spread acceptance and application in quantum chemistry, materials science and computational catalysis is in no way astonishing. However, it is also well known that standard density functionals underestimate the band gap in particular for small gap systems, and resultantly structural properties related to the band gap are difficult to predict. In quantum chemistry this has long be realized, and hybrid functionals mixing Hartree-Fock and local density functionals are generally preferred over purely local functionals. Such functionals usually predict a much larger band gap than purely local density functionals. With the exception of the Crystal code, hybrid functionals were not available in popular periodic codes, and only recently successful implementations and applications using plane wave based codes, such as VASP, were reported. In this talk, I will survey the expertise we have acquired for hybrid functionals for extended systems. For simple prototypical materials, such as metals, semiconductors, and insulators many ground state properties are indeed found to be in much better agreement with experiment than using purely local functionals. This concerns lattice constants and bulk moduli, but phonon dispersion relations are also often significantly improved, in particular, for those semiconductors where DFT predicts no band gap. Some specific applications will be discussed in detail. This includes the description of (small) polarons in semiconductors, the properties of ferroelectric materials (specifically BaTiO$_3$ and SrTiO$_3$), phonon dispersion relations in the group IV elements, and magnetic impurities in semiconductors. [Preview Abstract] |
Thursday, March 24, 2011 8:36AM - 9:12AM |
V6.00002: The effects of long-range exact exchange in hybrid-functional methods Invited Speaker: Over the past several years, hybrid density functional theory, which mixes a fraction of exact exchange into conventional semilocal exchange-correlation functionals, has become the dominant method used in molecular electronic structure calculations. While hybrid functionals are responsible for many successes of modern Kohn-Sham theory, they suffer from several drawbacks as well. The rapid decay of semilocal exchange causes errors in describing many phenomena, including charge transfer and Rydberg excitations, polarizabilities of long chains, and several others. Further, different properties seem to require different amounts of exact exchange; calculations near equilibrium, for example, appear to require less exact exchange than do calculations far from equilibrium. Including long-range exact exchange in finite systems improves accuracy in quantities sensitive to the long-range potential and makes it possible to treat systems both near and away from equilibrium on a fairly even footing. This talk discusses the motivations for including long-range exact exchange, as well as some remarkable successes and notable failures caused by doing so. Alternatives which attempt to retain most of the successes while eliminating most of the failures are also discussed. [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:48AM |
V6.00003: Structure of oxygen vacancies and electron localization on CeO$_2$(111) Invited Speaker: In the many applications of ceria-based materials in heterogeneous catalysis, the reducibility of ceria is essential to the catalytic function. Thus, having a theoretical approach that is able to describe the changes in the oxidation state of the multivalent cerium atoms appears desirable. The use of density functional theory with hybrid functionals is shown to be adequate [1]. It has been generally accepted that the electrons left behind upon oxygen removal from CeO$_2$ surfaces, driving the Ce$^{4+}$$\rightarrow$Ce$^{3+}$ reduction, localize on cationic sites in next-neighbor distance to the defect. We apply density-functional theory (DFT) with the HSE06 hybrid functional as well as the DFT+U approach and predict that vacancies on CeO$_2$(111) are likely to be bound to Ce$^{4+}$ ions rather than to Ce$^{3+}$ as priorly suggested. This prediction has been recently confirmed by means of STM imaging and spectroscopy [3]. We further find that subsurface vacancies are energetically preferred when compared to surface vacancies by up to 0.5 eV, and thus provide support for the most recent experimental result [4]. Defect-induced lattice relaxations are crucial to the electron localization on more distant cation sites to the defect and to the subsurface preference.\\[4pt] [1] J. L. F. Da Silva, M. V. Ganduglia-Pirovano, J. Sauer, V. Bayer, G. Kresse, Phys. Rev. B 75, 045121 (2007)\\[0pt] [2] M. V. Ganduglia-Pirovano, J. L. F. Da Silva, J. Sauer, Phys. Rev. Lett. 102, 026101 (2009).\\[0pt] [3] J. F. Jerratsch, X. Shao, N. Nilius, H-J Freund, C. Popa, M. V. Ganduglia-Pirovano, J. Sauer, unpublished.\\[0pt] [4] S. Torbr\"ugge et al., Phys. Rev. Lett. 99, 056101 (2007). [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:24AM |
V6.00004: Orbital-dependent functionals in FLAPW: hybrid functionals and optimized effective potentials Invited Speaker: Orbital-dependent functionals are a new class of exchange-correlation (xc) functionals for density-functional theory. Hybrid functionals combine a local or semi-local xc functional with a nonlocal orbital-dependent exchange functional and improve the band gaps of semiconductors and insulators as well as the description of localized states. As an alternative to nonlocal hybrid potentials, one can also construct local optimized effective potentials (OEP) from the exact exchange (EXX) functional. So far, most implementations for periodic systems use a pseudopotential plane-wave approach. We present an efficient all-electron, full-potential implementation of the PBE0 [1] and HSE [2] hybrid functionals as well as the OEP-EXX functional [3] within the FLAPW method ({\tt Fleur} code: www.flapw.de). Results for prototype semiconductors and insulators are in very good agreement with other implementations. We will demonstrate the improvement over conventional local or semilocal functionals for oxide materials and focus in particular on systems where standard functionals yield qualitatively wrong results. In particular, we will discuss the geometric and magnetic structures of EuO and GdN. Additionally, we will address the possibility of using the hybrid-functional ground state as starting point for a $GW$ quasiparticle correction [4] and show results for complex perovskite systems. \\[4pt] [1] M. Betzinger, C. Friedrich, and S. Bl\"ugel, Phys. Rev. B 81, 195117 (2010). \\[0pt] [2] M. Schlipf, M. Betzinger, C. Friedrich, M. Lezaic, and S. Bl\"ugel, inpreparation. \\[0pt] [3] M. Betzinger, C. Friedrich, S. Bl\"ugel, and A. G\"orling, to be published in Phys. Rev. B. \\[0pt] [4] C. Friedrich, S. Bl\"ugel, and A. Schindlmayr, Phys. Rev. B 81, 125102 (2010). [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 11:00AM |
V6.00005: Hybrid functional studies of InGaN alloys and oxides for photochemical watersplitting Invited Speaker: Photochemical watersplitting can potentially be a future sustainable energy source, converting sunlight and water into hydrogen. However, in order to have highly efficient devices materials are needed that absorb a large proportion of the solar spectrum while at the same time having valence and conduction bands that straddle the hydrogen and oxygen evolution redox potentials. It is well known that DFT consistently underestimates the band gap (the so-called ``band-gap problem''). As a consequence, the positions of the valence and conduction bands (and hence the band offsets) also suffer from uncertainties. To address these deficiencies of the local density approximation (LDA) and generalized gradient approximation (GGA) we use the HSE exchange correlation functional in order to accurately calculate the electronic band structure [1]. We will discuss bowing effects in InGaN alloys based on accurate calculation of band gaps of InGaN alloys and on an analysis of experimental results using our calculated deformation potentials to disentangle the effect of strain and alloying on the band gap. We will also discuss calculations of the absolute position of the valence band maximum and the conduction band minimum. Including a discussion and comparison with generalized gradient and local density approximations results. Finally we show that HSE may be used to understand the nature of surface defects. \\[4pt] [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003) [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700