Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z60: Modeling and Simulation of 2D Materials and DevicesRecordings Available

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Sponsoring Units: DMP Chair: Michele Pizzochero, Harvard Room: Hyatt Regency Hotel DuSable C 
Friday, March 18, 2022 11:30AM  11:42AM 
Z60.00001: An ab initio investigation of groups IIIV monochalcogenides Mateus Bazan Peters Querne, Jean M Bracht, Juarez Lopes Ferreira Da Silva, Anderson Janotti, Matheus Paes Lima Twodimensional (2D) materials have attracted a great attention due to their unusual properties such as high degree of anisotropy and chemical functionality over relatively large areas. Since the graphene breakthrough, a variety of 2D materials have been predicted, synthesized, and characterized, the most prominent family being the transitionmetal dichalcogenides, e.g., MoS_{2}, WSe_{2}, etc, representing semiconductors and topological semimetals. Inspired by the chemical flexibility and possible crystal structure variety, we consider the family of 2D monochalcogenides of the type MQ, where M = Al, Ga, In, Si, Ge, Sn, P, As, Sb; Q = S, Se, Te. Using density functional theory within the generalized gradient approximation (PBEsol) and hybrid functional calculations, we explore the possible crystal structure and electronic properties of this family of 2D MQ. For each compound we consider 12 crystal structures differing on space group, chemical bonding, and coordination, analyzing their electronic structure, band gaps, work function, and structural stability in terms of phonon spectra. The properties of these 2D materials are then compared to their 3D bulk parent structures, and a classification in terms of metallic versus semiconducting character, bonding and coordination is provided. 
Friday, March 18, 2022 11:42AM  11:54AM 
Z60.00002: Stability of layered In_{2}Se_{3} phases from Diffusion Quantum Monte Carlo calculations Igor D Evangelista, Anderson Janotti, Anouar Benali In_{2}Se_{3} is a semiconductor material that can be found in different crystal structures, most of them forming twodimensional layers stacked via van der Waals interactions. These layered crystal structures, composed of quintuple SeInSeInSe layers, differing on the stacking within the strongly bonded quintuple layer and across the van der Waals spacing, display electronic and optical properties that can be leveraged in a variety of device applications, including solar cells, photodetectors, and phasechange memory devices. However, the phase ordering and the transition between them remains unclear. Density functional theory and hybrid functional calculations show large variations in total energy differences between the different phases of In_{2}Se_{3}, dependent of the functional and the van der Waals correction used. Here we use diffusion Monte Carlo (DMC) calculations to determine the total energies and chargedensity differences between the three most common layered structures of In_{2}Se_{3}, namely, α, α’, and β, which differ in bonding/coordination within the quintuple layer and stacking of quintuple layers. Effects of temperature were also included by calculating the Helmholtz free energy, where the temperature dependence is included through the vibrational entropy. 
Friday, March 18, 2022 11:54AM  12:06PM 
Z60.00003: Degenerate excitons in strongly spinorbit coupled heterolayers Jiawei Ruan, Zhenglu Li, Chin Shen Ong, Steven G Louie We study the optical response and exciton properties of twodimensional topological systems with strong spinorbit coupling, using abinitio GW and BetheSalpeter equation (BSE) calculations. We develop a new method to derive group representations of exciton states directly from ab initio calculations without any assumption on the character of the envelope functions. Our analyses show that, for appropriate systems, it is possible for the two lowestenergy optically active excitons from a single valley to be degenerate. By construction of a smooth gauge, the envelope functions of these degenerate excitons exhibit 1slike characters. Our finding suggests these material systems are very promising for many applications in optoelectronics. 
Friday, March 18, 2022 12:06PM  12:18PM 
Z60.00004: Ab initio calculations of excitonphonon coupling in semiconducting systems Jacopo Simoni, Liang Tan, Vsevolod M Ivanov One of the most important lossy mechanisms in solid state systems is the 
Friday, March 18, 2022 12:18PM  12:30PM 
Z60.00005: BiAs as a novel 2D material Muhammad Zubair, Shaoib Khalid, Anderson Janotti Finding twodimensional semiconductors with large Rashba splitting is the vital step in the development of upcoming next generation spintronic technology as it assists the generation, detection and manipulation of spin current without magnetic field. Using firstprinciples calculations we find that BiAs is a stable layered semiconductors that crystalizes in a hexagonal honeycomb lattice geometry, with a narrow and indirect band gap. The inclusion of spinorbit coupling in the calculations reveals the presence RashbaDresselhaus type spin splitting located around Lpoint of the Brillion zone, with an elliptical spin texture and Rashba energy E_{R}= 66 meV and coupling constant α_{R} = 4.32 eVÅ. We also studied BiAs in monolayer form, and find a direct band gap semiconductor with a circular spin texture around Γ point, and Rashba energy and coupling constant of E_{R} = 17 meV and α_{R} = 1.56 eVÅ, which are large spinsplittting parameter for a 2D material. The effects of strain on the electronic structure of of the monolayer is also explored, and our results indicate that BiAs/AlN can potentially be used for the development novel fieldeffect transistors and spintronic devices. 
Friday, March 18, 2022 12:30PM  12:42PM 
Z60.00006: Firstprinciples calculation of the nonequilibrium quasiFermi levels in defective WSe_{2} pn junctions Tae Hyung Kim, Juho Lee, YongHoon Kim While the twodimensional pn junctions have been extensively studied for electronic and optoelectronic devices, the semiclassical approaches without considering atomistic details are still insufficient to describe its electronic structures, such as long depletion width and the role of defects. To overcome such limitations, we combine the multispace constrainedsearch density functional theory (MSDFT) formalism [1] together with the simulated doping method [2] for describing the doped pn junction under finitebias conditions. By calculating the lateral WSe_{2} pn junctions, we find that the charge density profile in the depletion region calculated within the firstprinciples approach is more diffuse than the analytical assumption, leading to a longer depletion width than the analytical expression. We then introduce Se (W) vacancy in the depletion region and show that as the forward bias voltage increases, the depletion width of the pdoped (ndoped) WSe_{2} decreases faster than that of the ndoped (pdoped) WSe_{2}. Thanks to the MSDFT that uniquely allows plotting quasiFermi level (QFL) profiles within the firstprinciples calculation, we also extract the QFL profiles in the defective WSe_{2} pn junction. Careful analysis of the QFL profiles shows that the asymmetrically varying depletion width in defective WSe_{2} pn junction originates from the asymmetrically penetrated QFL profiles mediated by the defect. Our findings highlight the importance of the firstprinciples approaches for 2D pn junction devices in terms of the design of nextgeneration 2D pn junction devices. 
Friday, March 18, 2022 12:42PM  12:54PM 
Z60.00007: Hydrogen Evolution Reaction on BP Monolayer and MoS_{2}/BP van der Waals Heterostructure from Firstprinciples Arunima Singh, Saswata Bhattacharya Molecular hydrogen is a sustainable energy carrier. One of the methods for its production is water splitting, whereby electrochemical hydrogen evolution reaction (HER) is efficiently catalyzed by Pt. Owing to its high cost, this field is being actively explored for earthabundant lowcost electrocatalysts like MoS_{2}. MoS_{2} is a promising acidstable catalyst; however, its applicability is limited by poor electrical transport and inefficient charge transfer at the interface. Therefore, the present work examines its bilayer van der Waals heterostructure (vdW HTS), which incorporates spatial separation of e^{}h^{+} on two layers. As per existing literature, the second constituent monolayer BP is advantageous as an electrode material, owing to its chemical stability in both oxygen and water environments. We have performed firstprinciples based calculations under the framework of density functional theory (DFT) for hydrogen evolution reaction in an electrochemical double layer on the BP monolayer and MoS_{2}/BP vdW HTS. The climbing image nudged elastic band method have been employed to determine the minimum energy pathways. The comparative study has been undertaken by analyzing their electrostatic potential and work function in Heyrovsky and Tafel reaction intermediates. Finally, we observe the Heyrovsky reaction path to be favorable. 
Friday, March 18, 2022 12:54PM  1:06PM 
Z60.00008: Extraordinary thermal conductivity of gold sulfide monolayers Armin Taheri, Simone Pisana, Chandra Veer Singh Gold sulfide monolayers (α, βAu_{2}S and α, β, γAuS) have emerged as a new class of twodimensional (2D) materials with appealing properties such as high thermal and dynamical stability, oxidation resistibility, and excellent electron mobility. However, their thermal properties are still unexplored. In this study, based on firstprinciples calculations and the PeierlsBoltzmann transport equation, we report the thermal conductivity (κ) and related phonon thermal properties of all members of this family. Our results show that gold sulfide monolayers have ultralow thermal conductivity within the range of 0.04 W m^1K^1 to 10.62 W m^1K^1, with different levels of anisotropy. Particularly, our results demonstrate that βAu_{2}S, having κ_{aa}= 0.06 W m^1K^1 and κ_{bb}= 0.04 m^1K^1 along the principal inplane directions, has one of the lowest κ values that have been reported for a 2D material. This extremely low thermal conductivity can be attributed to its flattened phonon branches and low phonon group velocity, high anharmonicity, and short phonon lifetimes. Our results may provide insight into the application of gold sulfide monolayers as thermoelectric materials, and motivate future κ measurements of gold sulfide monolayers. 
Friday, March 18, 2022 1:06PM  1:18PM 
Z60.00009: Intervalley excitonic hybridization, optical selection rules, and imperfect circular dichroism in monolayer hBN Fang Zhang, Chinshen Ong, Jiawei Ruan, Meng Wu, Xingqiang Shi, Zikang Tang, Steven G Louie We perform firstprinciples GW plus BetheSalpeter equation calculations to investigate the photophysics of monolayer hexagonal boron nitride (hBN), revealing excitons with novel kspace characteristics. The excitonic states forming the first and third peaks in its absorption spectrum are slike, but those of the second peak is notably plike, a first finding of strong cooccurrence of bright slike and bright plike states in an intrinsic 2D material. Moreover, even though the kspace wavefunction of these excitonic states are centered at the K and K'valleys like in monolayer transition metal dichalcogenides, the envelope functions of the basis excitons at one valley have significant extents to the basin of the other valley. As a consequence, the optical response of monolayer hBN exhibits a lack of circular dichroism, as well as a coupling that induces an intervalley mixing between s and plike states. 
Friday, March 18, 2022 1:18PM  1:30PM 
Z60.00010: Intercalation of Lithium inside Bilayer Buckled Borophene: A FirstPrinciples Prospective Sheeza Aslam It is the keen wish of scientists to develop anode materials having low volume expansion and large capacity with high mobility. Therefore, lithium (Li) has been intercalated in bilayer buckled borophene to improve the adsorption energy, theoretical capacity, opencircuit voltage (OCV), diffusion barrier, and structural stability. Here, we investigated the bilayer bborophene as anode material for Liion batteries using firstprinciple calculations. The intercalation of Li preserved the metallic nature of borophene and no volume expansion was found for a fully lithiated structure. This theoretical capacity of 1859 mAh/g, diffusion barrier 80 eV, and OCV 0.08 V indicate that intercalation improves said parameters compared to commercially used Graphene and prove it as a potential candidate for anode material in Liion batteries. 
Friday, March 18, 2022 1:30PM  1:42PM 
Z60.00011: A new material for Lithium and Sodium ion batteries: monolayer BPt_{2} Yelda Kadioglu, Can Ataca Liion and Naion battery technologies have been one of the most important studies recently due to their high efficiency in energy storage field. But still, the battery life is far from satisfying the users because of intrinsic issues of materials especially on electrolyte decomposition at high voltage and capacity attenuation through cycling. This is also restricting the further developments of electric devices. Therefore more effective materials are needed. We discovered a new twodimensional (2D) material BPt_{2} with extremely high storage capacity for Liion and Naion battery applications. This robust metallic monolayer does not lose its metallic character ,which is desirable for battery applications, even under external conditions such as strain and charging. The calculated low diffusion barrier of Li and Na on BPt_{2} monolayer makes it a promising candidate for next generation battery electrode material. Calculated open circuit voltages for multilayer structures using cluster expansion formalism and density functional theory simulations indicate that upto 3 layers of Li/Na can be stored between BPt_{2} layers. Therefore BPt_{2} layers promise to be an effective material for Liion and Naion battery electrode applications. 
Friday, March 18, 2022 1:42PM  1:54PM 
Z60.00012: Quantum capacitance of vertical tunnel fieldeffect transistors: A firstprinciples study Ryong Gyu Lee, Juho Lee, Tae Hyung Kim, YongHoon Kim The vertical twodimensional (2D) van der Waals (vdW) heterostructure has been intensively studied for the application of tunnel fieldeffect transistor (TFET) devices. Despite the similarities between TFET and capacitor architectures, the correlations between quantum capacitance and quantum transport characteristics have been rarely discussed. Carrying out firstprinciples finitebias nonequilibrium TFET simulations within the multispace constrainedsearch density functional theory (MSDFT) formalism we have recently developed [1], we elucidate the quantum transport and quantum capacitance properties of the graphenebased TFET in atomistic details. We show that the total capacitance of graphenebased TFET significantly deviates from the classical geometric capacitance due to the low quantum capacitance of graphene electrodes. Under applying the gatebias, we extract electrodespecific quantum capacitances and find that electrodes exhibit negative quantum capacitances raising the total capacitance at the resonanttunneling regime. Finally, we extend the study for the defective channel case and study how a point defect introduced within the inner channel region affects the capacitance and transport properties. Our findings provide fundamental insight into the nonequilbrium device characteristics of lowdimensional quantum devices and point towards a future direction for the design of 2D vdW heterojunction devices. 
Friday, March 18, 2022 1:54PM  2:06PM 
Z60.00013: Spatial mapping of disordered 2D systems: the conductance Sudoku Shardul Mukim, Mauro S Ferreira Motivated by recent advances on local conductance measurement techniques at the nanoscale, timely questions are being raised about what possible information can be extracted from a disordered graphene sheet by selectively interrogating its transport properties. We demonstrate how an inversion technique originally developed to identify the number of scatterers in a quantum device can be adapted to a multiterminal set up in order to provide detailed information about the spatial distribution of impurities on the surface of graphene, as well as other 2D material systems. The methodology input is conductance readings (for instance, as a function of the chemical potential) between different electrode pairs, the output being the spatially resolved impurity density. We show that the obtained spatial resolution depends on the number of such readings. Furthermore, by separating the impurity locations into partitions arranged in a gridlike geometry, this inversion procedure resembles a Sudoku puzzle in which the compositions of different sectors of a device are found by imposing that they must add up to specific constrained values established for the grid rows and columns. We argue that this technique may be used with other quantities besides the conductance, paving the way to alternative new ways of extracting information from a disordered material through the selective probing of local quantities. 
Friday, March 18, 2022 2:06PM  2:18PM 
Z60.00014: Direct and converse flexoelectricity in twodimensional materials Massimiliano Stengel, Miquel Royo, Matteo Springolo Flexoelectricity, the generation of macroscopic polarization or voltage in response to a strain gradient, is expected to play a prominent role in twodimensional (2D) crystals due to their extreme flexibility. Several attempts have been carried out to calculate the flexoelectric response of a monolayer (or few layers) due to a flexural deformation, but generally with remarkable disagreement in reported values. Here, building on recent developments in electronicstructure methods, we define and calculate the flexoelectric response of twodimensional materials fully from first principles. In particular, we show that the opencircuit voltage response to a flexural deformation is a fundamental linearresponse property of the crystal that can be calculated within the primitive unit cell of the flat configuration. Applications to graphene, silicene, phosphorene, BN and transitionmetal dichalcogenide monolayers reveal that two distinct contributions exist, respectively of purely electronic and latticemediated nature. Within the former, we identify a key \emph{metric} term, consisting in the quadrupolar moment of the unperturbed charge density. We propose a simple continuum model to connect our findings with the available experimental measurements of the converse flexoelectric effect. 
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