Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P7: FirstPrinciples Modeling of Excited State Phenomena VI: Semiconductors and OxidesFocus

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Sponsoring Units: DCOMP DMP DCP Chair: Emmanouil Kioupakis, University of Michigan Room: 266 
Wednesday, March 15, 2017 2:30PM  3:06PM 
P7.00001: Implementation of highly parallel and large scale GW calculations within the OpenAtom software Invited Speaker: Sohrab IsmailBeigi The need to describe electronic excitations with better accuracy than provided by band structures produced by Density Functional Theory (DFT) has been a longterm enterprise for the computational condensed matter and materials theory communities. In some cases, appropriate theoretical frameworks have existed for some time but have been difficult to apply widely due to computational cost. For example, the GW approximation (L. Hedin, \textit{Phys. Rev. }\textbf{139}, 1965) incorporates a great deal of important nonlocal and dynamical electronic interaction effects but has been too computationally expensive for routine use in large materials simulations.\\ \\OpenAtom is an open source massively parallel \textit{ab initio }density functional software package based on plane waves and pseudopotentials (\underline {http://charm.cs.uiuc.edu/OpenAtom/)} that takes advantage of the Charm$++$ parallel framework. At present, it is developed via a threeway collaboration, funded by an NSF SI2SSI grant (ACI1339804), between Yale (IsmailBeigi), IBM T. J. Watson (Glenn Martyna) and the University of Illinois at Urbana Champaign (Laxmikant Kale). We will describe the project and our current approach towards implementing large scale GW calculations with OpenAtom. Potential applications of large scale parallel GW software for problems involving electronic excitations in semiconductor and/or metal oxide systems will be also be pointed out. [Preview Abstract] 
Wednesday, March 15, 2017 3:06PM  3:18PM 
P7.00002: Band alignment at solidliquid interfaces from GW theory combined with continuum solvation models Johannes Lischner, Lars Blumenthal, Matthias Kahk, Paul Tangney Identifying efficient photocatalysts for the conversion of solar energy into fuels, such as hydrogen, constitutes a major challenge in the transition to a sustainable and renewable energy technology. A detailed understanding of the electronic structure of photoelectrodes, in particular the alignment of the electrode's electronic band edge positions with the relevant redox potentials of water, is required to guide experimental progress towards increased efficiencies. To address this problem, we introduce a new approach based on the combination of manybody perturbation theory within the GW approach for the electronic structure of the photoelectrode and joint densityfunctional theory for the description of solidliquid interfaces. We present results for several oxidebased photoelectrodes and find good agreement with experimental band edge positions. [Preview Abstract] 
Wednesday, March 15, 2017 3:18PM  3:30PM 
P7.00003: Firstprinciple study of phosphors for whiteLED applications : absorption and emission energies for Ce and Eudoped hosts. Xavier Gonze, Yongchao Jia, Anna Miglio, Matteo Giantomassi, Samuel Ponce, Masayoshi Mikami After the invasion of compact fluorescent lamps, white LED lighting is becoming a major contender in ecofriendly light sources, with a combination of yellow, green and/or redemitting phosphors partly absorbing the blue light emitted by an InGaN LED. After introducing the semiempirical Dorenbos model for 4f → 5d transition energies of rare earth ions, I present a firstprinciple study of two dozen compounds, pristine as well as doped with Ce3+ or Eu2+ ions, in view of explaining their different emission color. The neutral excitation of the ions is simulated through a constrained density functional theory method coupled with a delta SCF analysis of total energies, yielding absorption energies. Then, atomic positions in the excited state are relaxed, yielding emission energies and Stokes shifts, and identification of luminescent centers. In case of the Ce doped materials, the firstprinciple approach matches experimental data within 0.3 eV for both absorption and emission energies, covering a range of values between 2.0 eV and 5.0 eV, and provides Stokes shifts within 30\%, with two exceptions. This is significantly better than the semiempirical Dorenbos model. A similar analysis is performed for Eudoped materials, also examining the thermal quenching of two oxynitride hosts. [Preview Abstract] 
Wednesday, March 15, 2017 3:30PM  3:42PM 
P7.00004: CarrierInduced Transient Defect Formation and Nonradiative Recombination in InGaN LightEmitting Devices: A FirstPrinciples Study Junhyeok Bang, Yiyang Sun, J.H. Song, S. B. Zhang Nonradiative recombination (NNR) of excited carriers is not only one of the fundamental physical processes in materials, but is also crucial to optoelectronics device efficiency. Until now, ShockelyReadHall and Auger recombination are the two main nonradiative recombination mechanisms widely discussed. Here, by using firstprinciples calculations, we propose a new NRR mechanism, where excited carriers recombine via a Frenkelpair (FP) defect formation and the carrier energy is dissipated to phonon through defect generation and annihilation processes. While in the ground state the FP is high in energy and is unlikely to form, its formation is enabled in the electronic excited states by a strong electronphonon coupling of the excited carriers. This NRR mechanism is expected to be generally observed in widegap semiconductors, rather than being limited to InGaNbased light emitting devices. [Preview Abstract] 
Wednesday, March 15, 2017 3:42PM  3:54PM 
P7.00005: Optical response of semiconductors in a dcelectric field Lucie Prussel, Valerie Veniard A deep understanding of the optical properties of solids is crucial for the improvement of nonlinear materials and devices. It offers the opportunity to search for new materials with specific properties. One way to tune some of those properties is to apply an electrostatic field. This gives rise to electrooptic effects. The most known among those is the Pockel or linear electrooptic effect (LEO), which is a second order response property described by the susceptibility $\chi^{(2)}(\omega;\omega,0)$. An important nonlinear process is the second harmonic generation (SHG), where two photons are absorbed by the material. While this process is sensitive to the symmetry of the material, adding a static field would enable a nonlinear response from every material, including centrosymmetric ones. This happens through a third order process, named EFISH (Electric Field Induced Second Harmonic) for which the susceptibility of interest is $\chi^{(3)}(2\omega;\omega,\omega,0)$. We have developed a theoretical approach and a numerical tool to study these two nonlinear properties (LEO and EFISH) in the context of Timedependent Density Functional Theory (TDDFT), and we have applied it to the case of bulk SiC and GaAs as well as layered systems such as Ge/SiGe. [Preview Abstract] 
Wednesday, March 15, 2017 3:54PM  4:06PM 
P7.00006: RealSpace Analysis of the Optical Absorption in Alternative Phases of Silicon Chin Shen Ong, Sinisa Coh, Marvin L. Cohen, Steven G. Louie We introduce a realspace approach to understand the relationship between optical absorption and crystal structure. This approach is applied to some alternative phases of silicon in addition to the diamond structure, with a focus on the Si$_{20}$ crystal phase as a case study. We find that about 83{\%} of the enhancement in the calculated lowenergy absorption in Si$_{20}$ can be attributed to reducing the differences between the onsite energies of the bonding and antibonding orbitals as well as to increasing the magnitude of the hopping integrals for specific SiSi bonds. This work was supported by NSF grant No. DMR1508412 and the DOE under Contract No. DEAC0205CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility. [Preview Abstract] 
Wednesday, March 15, 2017 4:06PM  4:18PM 
P7.00007: Nearedge optical properties of $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ determined through firstprinciples calculations Kelsey Mengle, Guangsha Shi, Dylan Bayerl, Emmanouil Kioupakis $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ is a wide bandgap material of interest for many applications, including highpower electronics and optoelectronics. The electronic and optical properties are especially interesting due to its wide band gap, reported in the literature between 4.45.0 eV. We use firstprinciples calculations including density functional theory (DFT) and manybody perturbation theory (GW) to investigate the discrepancy in the reported values of the fundamental band gap and whether the nature is direct or indirect. We find that the band gap is indirect but only 29 meV lower in energy than the direct gap. By comparing the imaginary part of the dielectric function to the calculated optical matrix elements for $\Gamma $$\Gamma $ electronic transitions, we verify the directionaldependence of the absorption onsets for the material. This anisotropy can explain the broad range of reported band gaps. The calculated radiative recombination coefficients demonstrate that despite being an indirectgap material, intrinsic deepUV light emission is possible with $\beta $Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ at high excitation. [Preview Abstract] 
Wednesday, March 15, 2017 4:18PM  4:30PM 
P7.00008: Schottky junctions studied using KorringaKohn–Rostoker nonequilibrium Green’s function method Hisazumi Akai, Masako Ogura A scheme that combines the nonequilibrium Green’s function method with the KorringaKohnRostoker (KKR) Green’s function method is proposed. The method is different from many previous attempts in that it uses the exact Green’s function whose spectrum is not bound within a finite energy range, and hence, provides sound basis for quantitative discussions. The scheme is applied to the Schottky junctions composed of an Al/GaN/Al trilayer. Schottky contacts formed in metal/semiconductor junctions play an important role in semiconductor devices and integrated circuits. They have been intensively investigated for several decades not only for possible application to electronic devices but also for gaining a fundamental understanding of the Schottky barrier formation. Our results show that the Schottly barrier is formed between an undoped GaN and Al interface. The transport property of this system under various finite bias voltages is calculated. It is shown that the asymmetric behavior of electron transport against the direction of bias voltage occurs in this system, confirming the feature of rectification. [Preview Abstract] 
Wednesday, March 15, 2017 4:30PM  4:42PM 
P7.00009: Electronic correlations in FeSb$_2$: a QSGW+DMFT investigation Walber Hugo De Brito, Sangkook Choi, Gabriel Kotliar Optical conductivity measurements of iron antimonide (FeSb$_2$) have shown that a large spectral weight redistribution takes place when the material is cooled down to 10 K [1]. On the theoretical side, density functional theory and GW calculations are known to predict metallic and insulating phases with a too large band gap, respectively. These findings suggest that electron correlations are relevant for the gap formation in FeSb$_2$ and that a theoretical description beyond a manybody perturbation theory is required. In this study we investigate from an \textit{ab initio} perspective the role played by electron correlations on the electronic properties of FeSb$_2$. With our combined quasiparticle selfconsistent GW (QSGW) and dynamical mean field theory (DMFT) calculations we reveal that manybody correlation effects lead to a temperature dependent gap renormalization. In particular, our calculations indicate that the dynamical behavior of the real parts of valence and conduction selfenergies is of great importance to the gap formation in FeSb$_2$. [1] Phys. Rev. B {\bf 82}, 245205 (2010). [Preview Abstract] 
Wednesday, March 15, 2017 4:42PM  4:54PM 
P7.00010: Quasiparticle selfconsistent GW calculation of the band structure of $\beta$Ga$_2$O$_3$ Amol Ratnaparkhe, Walter Lambrecht $\beta$Ga$_2$O$_3$ has recently received attention as an ultra wide band gap oxide. There are still uncertainties over its basic electronic structure. Here we present QSGW calculations of the band structure implemented in the linearized muffintin orbital approach. The QSGW approach usually overestimates the band gap, due to the underestimated screening in the random phase approximation (RPA) used to calculate $W$. Even after taking into account a universal 0.8 correction factor for this effect, we find a gap of order 5.4 eV, significantly higher than experimental values for the absorption onset. After inclusion of a lattice polarization effect on the screening, we find a minimum direct gap at $\Gamma$ of 4.9 eV. The zeropoint motion correction is estimated to be another 0.2 eV, leading to a final gap of 4.7 eV in good agreement with experiment. The indirect gap is found to be about 0.1 eV smaller. Symmetry labeling the states near the VBM and CBM at $\Gamma$ shows that the lowest gap at $\Gamma$ is allowed for ${\bf E}\perp{\bf b}$, and the first transition allowed for ${\bf E}\parallel{\bf b}$ occurs 0.6 eV higher. This predicted shift of the absorption onset for different directions is larger than found in experiment. Calculated absorption curves will be presented. [Preview Abstract] 
Wednesday, March 15, 2017 4:54PM  5:06PM 
P7.00011: Surfaces and interfaces of topological insulators from relativistic manybody calculations Irene Aguilera, Christoph Friedrich, Stefan Blugel We introduce the $GW$ and QS$GW$ methods where the spinorbit coupling is incorporated directly into the selfenergy. This is critical to obtain reliable results for topological insulators (TIs) [1]. Within the allelectron FLAPW formalism, we show calculations for Bi [2] and TIs of the Bi$_2$Se$_3$ family [3]. Comparison to photoemission spectroscopies [4,5] shows that the manybody bulk and surface electronic structures agree much better to experiments than the ones from density functional theory (DFT). For example, we show that Bi$_2$Se$_3$ is a direct gap semiconductor [5], in contrast to predictions by DFT. For the description of surfaces of TIs as well as interfaces between TIs and between a TI and a trivial material, we use a basis of Wannier functions to construct slab Hamiltonians. This approach allows us to study very large systems with a high accuracy. [1] Aguilera \textit{et al.}, Phys. Rev. B \textbf{88}, 165136 (2013). [2] Aguilera \textit{et al.}, Phys. Rev. B \textbf{91}, 125129 (2015). [3] Aguilera \textit{et al.}, Phys. Rev. B \textbf{88}, 045206 (2013). [4] Michiardi \textit{et al.}, Phys. Rev. B \textbf{90}, 075105 (2014). [5] Nechaev \textit{et al.}, Phys. Rev. B \textbf{87}, 121111(R) (2013). Correspondence: i.aguilera@fzjuelich.de [Preview Abstract] 
Wednesday, March 15, 2017 5:06PM  5:18PM 
P7.00012: A new DFT approach to model small polarons in oxides with proper account for longrange polarization Sebastian Kokott, Sergey V. Levchenko, Matthias Scheffler In this work, we address two important challenges in the DFT description of small polarons (excess charges localized within one unit cell): sensitivity to the errors in exchangecorrelation (XC) treatment and finitesize effects in supercell calculations. The polaron properties are obtained using a modified neutral potentialenergy surface (PES) [1]. Using the hybrid HSE functional and considering the whole range $0\leq\alpha\leq 1$, we show that the modified PES model significantly reduces the dependence of the polaron level and binding energy in MgO and TiO$_2$ on the XC functional. It does not eliminate the dependence on supercell size. Based on Pekar's model [2], we derive the proper longrange behavior of the polaron and a finitesize correction that allows to obtain the polaron properties in the dilute limit (tested for supercells containing up to 1,000 atoms). The developed approach reduces drastically the computational time for exploring the polaron PES, and gives a consistent description of polarons for the whole range of $\alpha$. It allowed us to find a selftrapped hole in MgO that is noticeably more stable than reported previously.[1] B. Sadigh \textit{et al.}, Phys. Rev. B \textbf{92}, 075202 (2015); [2] S.I. Pekar, Zh. Eksp. Teor. Fiz. \textbf{16}, 335 (1946). [Preview Abstract] 
Wednesday, March 15, 2017 5:18PM  5:30PM 
P7.00013: GW Calculations of Bulk and Fewlayer SnO Yabei Wu, Weiwei Gao, Weiyi Xia, Wei Ren, Peihong Zhang Layered structure tin monoxide (SnO) has emerged as a promising materials for a variety of applications ranging from batteries to optoelectronics. Recently, fewlayer field effect transistors (FETs) using the tetrahedral (layerstructure) SnO material have been fabricated successfully recently [1]. The carrier mobility is shown to be as good as that of other 2D FETs [1]. We have carried out quasiparticle (QP) calculations within the GW approximation to understand the electronic properties of bulk and fewlayer SnO. Density functional theory within the local density approximation (LDA) or generalized gradient approximation (GGA) predicts a semimetallic band structure. Upon including the selfenergy effects, the QP band gap is 0.75 eV, in good agreement with experiment. We will also discuss the layerdependence of the QP properties of SnO. [1] Saji, Kachirayil J., et al. Advanced Electronic Materials (2016). [Preview Abstract] 
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