Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D12: Electronic Structure: Theory and SpectraRecordings Available
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Sponsoring Units: FIAP Chair: Ying Liu, Pennsylvania State University Room: McCormick Place W-181C |
Monday, March 14, 2022 3:00PM - 3:12PM |
D12.00001: Structure and Properties of Ab-initio Predicted BxAl1−xN Alloys Cody L Milne, Tathagata Biswas, Arunima K Singh Ultra-wide band gap (UWBG) materials offer a promising avenue for the future of power electronics. Devices made from UWBG materials can operate at much higher voltages, frequencies, and temperatures than the current silicon devices, and could miniaturize the current electrical power conversion systems. Device performance is strongly correlated with the band gap of the material. Thus UWBG materials with large band gaps such as aluminum nitride and boron nitride, in addition to their high thermal conductivity and mechanical strength, could revolutionize power electronics. This study investigates the structure of BAlN and its band gap energy over a range of boron molar fractions. Formation energies were used as a basis for fitting a cluster expansion for BxAl1−xN structures and used to predict ground state structures over a range of boron concentration. A novel high-throughput workflow was utilized to calculate band structures for the ground state structures using DFT and GW methods. Band gap energies, impact ionization rates, and effective masses were also calculated for the ground state structures. |
Monday, March 14, 2022 3:12PM - 3:24PM |
D12.00002: Electronic Structure of InAs and InSb Surfaces: Density Functional Theory (DFT) and Angle-Resolved Photoemission Spectroscopy (ARPES) Shuyang Yang, Niels B Schröter, Vladimir N Strocov, Sergej Schuwalow, Mohana Rajpalke, Keita Ohtani, Peter Krogstrup, Georg W Winkler, Jan Gukelberger, Dominik Gresch, Gabriel Aeppli, Roman M Lutchyn, Noa Marom The electronic structure of surfaces plays a key role in the properties of quantum devices. However, surfaces are also the most challenging to simulate and engineer. We study the electronic structure of InAs(001), InAs(111), and InSb(110) surfaces using a combination of DFT and ARPES. Large-scale DFT simulations are enabled by using a machine-learned Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. To facilitate direct comparison with ARPES, we implemented a "bulk unfolding" scheme for projecting the calculated band structure of a supercell surface slab model onto the bulk primitive cell. For all three surfaces, DFT is in good agreement with ARPES. For InAs(001), simulations clarify the effect of surface reconstruction. Different reconstructions produce distinctive surface states, which may be detected by ARPES with low photon energies. For InAs(111) and InSb(110), simulations help elucidate the effect of oxidation. Owing to larger charge transfer from As to O than from Sb to O, oxidation of InAs(111) leads to significant band bending and produces an electron pocket, whereas oxidation of InSb(110) does not. Our combined theoretical and experimental results may inform the design of quantum devices involving InAs and InSb, e.g., Majorana-based qubits. |
Monday, March 14, 2022 3:24PM - 3:36PM |
D12.00003: Ab-initio Self-Consistent Density Functional Theory Description of Rock-Salt Magnesium Selenide (MgSe) Yuriy Malozovsky, Blaise A Ayirizia, Uttam Bhandari, Lashounda Franklin, Diola Bagayoko We report comprehensive results from density functional theory (DFT) calculations of electronic, transport, and bulk properties of rock-salt magnesium selenide (MgSe). We utilized a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) method. We performed a generalized minimization of the energy using successive, self-consistent calculations with augmented basis sets. We verifiably attained the ground state of the material. Therefore, our results possess the full physical content of DFT. Our calculated, indirect bandgap is 2.49 eV for a room temperature lattice constant of 5.460Å. We present the ground-state band structure and the total and partial densities of states, DOS and PDOS, respectively. Electron and hole effective masses were calculated for the material. Results are discussed and shown to be in reasonable agreement with available experimental data. Our calculated bulk modulus of 63.1 GPa is in excellent agreement with the experimental value of 62.8 ± 1.6 GPa. Our predicted equilibrium lattice constant, at zero temperature, is 5.424Å with a corresponding indirect bandgap of 2.51 eV. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D12.00004: Property Exploration and Structure Prediction of Eu-including Defect-Resistant I2-Eu-IV-X4 (I = Li, Cu, Ag; IV = Si, Ge, Sn; X = S, Se) Chalcogenide Semiconductors Tianlin Wang, Yi Yao, Garrett Wessler, Volker Blum, David B Mitzi We present a first-principles investigation, using all-electron hybrid density functional theory, of the chalcogenide semiconductors I2-II-IV-X4 (I = Li, Cu, Ag; II = Ba, Sr, Eu, Pb; IV = Si, Ge, Sn; X = S, Se) with the rare-earth (RE) element Eu situated on the II site. Employing these computational approaches and the HSE06 hybrid functional, we examine the validity of a tolerance factor approach developed previously by our team to predict and rationalize the occurrence of different, potentially thermodynamically stable structures, and show agreement between the two approaches in terms of predicting preferred structures. The electronic, optical, and magnetic properties of target compounds were also analyzed using the spin-orbit coupled HSE06 hybrid functional. The description of the Eu 4f states matches benchmark ARPES experiments for Eu-including compounds reported in the literature. Based on the nature of their band structures, as well as band gap values, Cu2EuGeSe4, Cu2EuSnS4 and Cu2EuSnSe4 are identified as potential candidate materials for photovoltaic applications. The compounds are found to be paramagnetic, consistent with experimental results. |
Monday, March 14, 2022 3:48PM - 4:00PM |
D12.00005: Multi-code Benchmark on Ti K-edge X-ray Absorption Spectra of Ti-O Compounds John Vinson, Fanchen Meng, Senser Selcuk, Mark S Hybertsen, Benedikt Maurer, Christian W Vorwerk, Claudia Draxl, Xiaohui Qu, Deyu Lu X-ray absorption spectroscopy (XAS) is an element-specific characterization technique that is sensitive to a material's structure and electronic properties. First-principles XAS simulations have been widely used as to interpret spectra and draw physical insights. Recently, there has also been a growing interest in building computational XAS databases to enable machine learning applications. While several codes are widely used to calculate XAS, non-trivial differences exist both in their underlying formalism and implementation. A systematic comparison between these codes is crucial for assessing reliability and reproducibility of computational XAS data. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D12.00006: Excitonic States in an Ellipsoidal Quantum Dot with Kane's Dispersion Law Karen Dvoyan, Abdennaceur Karoui, Branislav Vlahovic Electronic and excitonic states in an InSb ellipsoidal quantum dot (QD) with complicated dispersion law are theoretically investigated within the framework of the geometric adiabatic approximation in the strong, intermediate, and weak quantum confinement regimes. For the lower levels of the spectrum, the square root dependence of energy on QD sizes is revealed in the case of Kane’s dispersion law. The obtained results are compared to the case of a parabolic (standard) dispersion law of charge carriers. The possibility of the accidental exciton instability is revealed for the intermediate quantum confinement regime. For the weak quantum confinement regime, the motion of the exciton's center-of-gravity is quantized, which leads to the appearance of additional Coulomb-like sub-levels. It is revealed that in the case of the Kane's dispersion law, the Coulomb levels shift into the depth of the forbidden band gap, moving away from the quantum confined level, whereas in the case of the parabolic dispersion law, the opposite picture is observed. The corresponding selection rules of quantum transitions for the interband absorption of light are obtained. New selection rules of quantum transitions between levels conditioned by 2D exciton center of mass vertical motion quantization in a QD is revealed. The absorption threshold behavior characteristics depending on the QD's geometrical sizes are also revealed. |
Monday, March 14, 2022 4:12PM - 4:24PM |
D12.00007: The Importance of Avoided Crossings in Understanding Band Convergence in Half-Heusler Thermoelectric Semiconductors Madison Brod, G. Jeffrey Snyder, Shashwat Anand When designing high-performance thermoelectric (TE) semiconductors, it is greatly beneficial to engineer electronic bands that have high valley degeneracy, NV, or multiple carrier pockets near the transport edge. High NV can be achieved by having band extrema at low symmetry points in the Brillouin zone (BZ) and by having multiple band extrema converged within a few kBT. Half-Heusler (hH) compounds comprise a promising class of TEs that benefit from low cost, low toxicity, and high stability. While there are dozens of known base compositions (XYZ) for hH TEs, they can be categorized into just three categories based on the location of the valence band maximum (VBM) in the BZ (at L, W or Γ). Thus, the performance of p-type hH TEs is improved when the lower-symmetry VBMs (L or W) are favored or when two or more of the competing VBMs are converged. While high-throughput density functional theory (DFT) calculations have helped identify chemical trends for predicting the VBM location, there has been no consistent explanation of their origins. In this work, we show that avoided crossings are key to understanding the origins of the three VBMs and their relative energies. We employ DFT, group theory, and tight binding to describe the interactions responsible for these avoided crossings. |
Monday, March 14, 2022 4:24PM - 4:36PM |
D12.00008: Ab-initio computations of electronic, transport, and structural properties of zinc-blende beryllium sulfide (zb-BeS) Yuriy Malozovsky, Blaise A Ayirizia, Janee Brumfield, Diola Bagayoko We have studied the electronic, structural, and transport properties of the zinc-blende beryllium sulfide (zb-BeS), using density functional theory (DFT). We employed a Local Density Approximation (LDA) potential and the Linear Combination of Atomic Orbitals (LCAO). Our computational method leads to the ground state of the materials without utilizing over-complete basis sets. Our calculated, indirect band gap is 5.44 eV, from Г to a conduction band minimum between Г and X, for a room temperature lattice constant of 4.863 Å, is in excellent agreement with experiment which indicates the lower limit of 5.5 eV for the indirect band gap. We also report the total (DOS) and partial densities of states (pDOS), electron and holes effective masses, the equilibrium lattice constant, and the bulk modulus. Our calculated bulk modulus of 107.7 GPa is in excellent agreement with experiment (105 GPa). Our predicted equilibrium lattice constant at zero temperature is 4.814 Å. |
Monday, March 14, 2022 4:36PM - 4:48PM |
D12.00009: Electronic structure and local vibrational modes of Ni doped CdS: Crystal field splitting, Jahn-Teller instability, and on-site Coulomb correlation effects Greis J. Cruz, Zhao Tang, Peihong Zhang Doping transition metals (TMs) such as Ni in CdS quantum dots (QDs) have been shown to improve their photocatalytic activities[1-4], but the underlying mechanism is still not understood. TMs are well-known for their rich chemistry due to their variable oxidation states, high degree of electronic degeneracy, and ability and flexibility to form complexes with reagents. We have carried out density functional theory (DFT) plus U studies of Ni-doped CdS. A T2 ⊗ (e+t2) Jahn-Teller (JT) model is developed to understand the ground state adiabatic potential energy surface (APES). We find that the interplay among crystal-field splitting, JT distortion, on-site Coulomb correlation, and magnetism results in the appearance of active states near the conduction band minimum. Therefore, introducing TM dopants in CdS QDs can not only provide reaction sites but also introduce near-edge electronic states that can enhance photo-absorption or fine-tune the band alignment for selective photocatalytic reactions. Our work also contributes to a deeper understanding of the interplay among various degrees of freedom in defect physics. |
Monday, March 14, 2022 4:48PM - 5:00PM |
D12.00010: Nonlinear Properties of Monolayer Transition Metal Dichalcogenide Systems Nicholas A Pike, Ruth Pachter The second-order nonlinear optical properties of monolayer transition metal dichalcogenides (TMDs) have been drawing increased interest for device applications, yet, challenges remain in the measurements of their nonlinear responses. In this work, we report a first-principles analysis of the second-order nonlinear optical response of monolayer TMDs (group V and VI) in their hexagonal form and as hexagonal Janus TMDs. These calculations are useful for benchmarking and understanding trends across different TMD compositions. We compare to experimental measurements when available and find that the nonlinear optical properties of these materials are comparable to other bulk materials currently used in electro-optical devices. Given the magnitude of the second-order nonlinear optical properties and the two-dimensional nature of these materials, avenues are opening for reducing the size of electro-optical devices by using monolayer TMDs. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D12.00011: Thickness dependence of the electronic and magnetic structure of a correlated van der Waals magnet, CrPS4. Alexandria R Alcantara, Christopher A Lane, Jason T Haraldsen, Roxanne M Tutchton In this study, we examine the electronic and magnetic structure of CrPS4, a 2D magnetic semiconductor, by employing the SCAN meta-GGA density functional yielding magnetic moments and band gaps in excellent agreement with experiment across 2D and correlated material classes. We find that the magnetic configurations considered, thus far, predict the experimentally observed A-type antiferromagnetic (A-AFM) ordered ground state, with a magnetic moment of 2.77??B per chromium atom. To gain insight into the evolution of the ground state with thickness, the total energy of each magnetic configuration is calculated for a variety of thicknesses, where a monolayer of CrPS4 is predicted to be a ferromagnetic (FM) insulator with a band gap of 1.379 eV, A-AFM bilayer with 1.367 eV band gap, and A-AFM trilayer with a 1.341 eV band gap. Using the theoretically determined classical energy for each magnetic configuration, we compare the total energies from DFT and estimate the exchange interactions as a function of thickness. |
Monday, March 14, 2022 5:12PM - 5:24PM |
D12.00012: Chain Model of Charge Transfer and Application to Contact Electrification Javier E Hasbun, L. C. Lew Yan Voon, Morten Willatzen Contact electrification refers to the motion of charges through friction or even the contact between two materials. Electron transfer models seem to be good candidates for understanding the charge transfer process. This topic is closely related to explanations of static electricity as well as lightning during thunderstorms, sandstorms, and volcanic plumes. A better understanding of contact electrification should help meet future population power needs. Here we work with a previously introduced quantum mechanical chain model of contact electrification and study the charge transfer on a single chain with analytical results. The model is amenable to study the charge dynamics for a chain of atoms with symmetric and asymmetric hopping. Analytic and numeric results are shown to give rise to similar dynamics in both the absence and presence of electron interactions. We extend the chain model to the case of two atoms per cell (a perfect alloy system) and further apply it to contact electrification between two materials. The effect of increasing the magnitude of the contact transfer matrix element is studied. |
Monday, March 14, 2022 5:24PM - 5:36PM |
D12.00013: Theoretical study on symmetries and properties of three-dimensional valleytronic systems Manabu Takeichi, Shuichi Murakami Materials with spin-split valleys showing direct bandgaps, such as transition metal dichalcogenides, have been attracting interest in the context of valleytronics. All such materials known so far are two-dimensional. In this talk, we show a list of space groups to realize three-dimensional materials with such a valley degree of freedom. For this purpose, we made some criteria for space groups allowing valleys with good properties for valleytronics, and we find that there are only a few space groups that satisfy all of these criteria. Moreover, we propose a model which possesses inequivalent six valleys, and reveal its properties in the context of valleytronics, such as spin-valley coupling, nonzero Berry curvature, and some ways of controlling these valleys. |
Monday, March 14, 2022 5:36PM - 5:48PM |
D12.00014: Anderson localization of electron states in Al-Pd-Re quasicrystal Sudipta Roy Barman, Shuvam Sarkar, Marian Krajci, Pampa Sadhukhan, Vipin K Singh, Andrei Gloskovskii, Prabhat Mandal, Vincent Fournee, Marie-Cecile de Weerd, Julian Ledieu, Ian R Fisher The influence of disorder on the critical electron states in a quasiperiodic lattice is a subject of intense research. In this work, we apply using hard x-ray photoelectron spectroscopy, density functional theory and resistivity to establish occurrence of Anderson localization in a so-called "semiconducting" icosahedral quasicrystal Al-Pd-Re due to site disorder. Anderson localization is observed in polygrain Al-Pd-Re, whose conductivity is an order of magnitude reduced compared to the single-grain monocrystalline Al-Pd-Re. Curiously however, the spectral intensity of the localized electron states is enhanced at the Fermi level in the former. These extra states originate primarily from Re 5d- Pd 4d hybridization, and are enhanced in polygrain i-Al-Pd-Re due to compositional difference, but are broadened because of disorder that brings about Anderson localization. This is established by the Mott variable range hopping behavior of conductivity, and the estimated localization length is 23 Å. In contrast, the spectral shape of sg-Al-Pd-Re portrays a well-formed pseudogap, and exhibits excellent agreement with the valence band calculated for ordered Al-Pd-Re, indicating absence of anderson localization. |
Monday, March 14, 2022 5:48PM - 6:00PM |
D12.00015: Density functional theory investigation of highly conductive Ti sub-oxides for nanoelectromechanical systems (NEMS) switches Mehmet G Sensoy Nanoelectromechanical (NEMS) switches are potential next-generation electronic computing devices due to their small scale, low power consumption, and (relatively) high speed. They consume 0.1 to 0.01 the power of conventional solid-state transistors. Their widespread adoption requires a new, fundamental understanding of the phenomena controlling interfacial adhesion and electrical contact resistance under in operating environments. This work focuses on conductive oxides as contact materials because of their wear resistance and resistance to a wide range of environmental degradation that plagues more traditional metallic contacts. Ti sub-oxides (TinO2n-1) are good candidates due to their metallic conductivity, environmental and low cost compared with other conductive oxides. In this work, we shed light into the questions of how amorphization and crystallization of the Ti sub-oxides occur using ab initio molecular dynamics simulations. From this, we determine the electrical conductivity of Ti sub-oxides with different phases. |
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