Computational Materials Discovery and Optimization – From Bulk to Materials Interfaces and 2D Materials: 2D Materials and Materials Epitaxy
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Richard Hennig, University of Florida; Arunima Singh, Lawrence Berkeley National Laboratory; Dallas Trinkle, University of Illinois, Urbana-Champaign; Eric Homer, Brigham Young University

Monday 2:00 PM
February 27, 2017
Room: 11A
Location: San Diego Convention Ctr

2:00 PM  Invited
Polyphony in B Flat -- Is the Two-dimensional Boron Truly Emerging?: Boris Yakobson1; Yuanyue Liu2; 1Rice University; 2Caltech
    Unlike well-studied growth and morphology of graphene,1 growth of binary compositions2 of h-BN or MX2, or at least well-defined phosphorene,3 pure mono-elemental boron so far remains elusive newcomer: which of so many possible polymorphs are actually forming in experiments remains debated.4 We will discuss how theory has accelerated experimental discoveries, and what challenges in determining the exact 2D-boron makeup are still on the way to testing its promising properties.5 References: [1] VArtyukhov et al. Phys. Rev. Lett. 114, 115502 (2015); YHao et al. Nature Nanotech. 11, 426 (2016); FXu et al. Nano Lett. 16, 34 (2016). [2] ZZhang et al. Nano Lett. 16, 1398 (2016); VArtyukhov, ZHu et al. Nano Lett. 16, 3696 (2016). [3] YLiu et al. Nano Lett. 14, 6782 (2014); LWang et al. Nanoscale, 7, 9746 (2015). [4] ZZhang et al. Nature Chem. 8, 525 (2016). [5] EPenev, AKutana et al. Nano Lett. 16, 2522 (2016).

2:30 PM  
Topology-Scaling Identification of Layered Compounds and Stable Exfoliated 2D Materials: Michael Ashton1; Joshua Paul1; Susan Sinnott2; Richard Hennig1; 1University of Florida; 2Pennsylvania State University
    We search the Materials Project crystal structure database for materials possessing layered motifs in their crystal structures using a topology-scaling algorithm. The algorithm identifies and measures the sizes of bonded atomic clusters in the structure's unit cell, and determines their scaling with cell size to identify two-dimensional structural motifs. The search yields 829 stable layered materials, which are considered as candidates for the formation of two-dimensional materials via exfoliation. Density-functional calculations for these candidate materials yield 609 monolayers with exfoliation energies below those of certain already-extant monolayers. In addition to being candidates for synthesis, the crystal structures of these monolayers can be used as templates for future theoretical searches for stable two-dimensional materials. The search identifies over 250 unique prototype two-dimensional materials. We provide the complete list of optimized structures and other data for all 829 two-dimensional materials in our open database at

2:50 PM  
Two-Dimensional Multiferroics for Novel Multifunctional Mechano-Opto-Electronic Devices: Hua Wang1; Xiaofeng Qian1; 1Texas A&M University
    Low-dimensional multiferroic materials with coupled ferroic orders, though highly valuable for miniaturized devices, are scarce due to the stringent symmetry and chemistry requirements for practical applications at room temperature. Using first-principles theory, we predict that two-dimensional monolayer Group IV monochalcogenides including GeS, GeSe, SnS, and SnSe are a class of 2D semiconducting multiferroics thermodynamically stable at room temperature with strongly coupled giant in-plane spontaneous ferroelectric polarization and ferroelastic strain. Their optical absorption spectra exhibit large in-plane anisotropy with visible-spectrum excitonic gaps and sizable binding energies. These unique electronic structures together with low domain wall energy and small migration barrier make them promising for tunable multiferroic functional devices by manipulating external electrical, mechanical, and optical field to control the internal responses. This may allow the realizations of 2D ferroelectric memory, 2D ferroelastic memory, 2D ferroelastoelectric nonvolatile photonic memory, and 2D ferroelectric excitonic photovoltaics. (Reference: arXiv:1605.03903 (2016))

3:10 PM  
Opening Electronic Band Gaps in 2D Materials by Deformation Twins: Dingyi Sun1; David Rojas2; Mauricio Ponga2; 1California Institute of Technology; 2University of British Columbia
    Twinning - a process by which the crystal lattice reorients itself symmetrically across a planar discontinuity - is an important mechanism by which many materials (particularly, hexagonal close-packed) accommodate deformation. As a follow-up to the previously-developed twinning genome, which predicted twinning for a variety of 3D materials, we apply its concepts to 2D materials. We first identify all possible twins. We then perform molecular dynamics simulations, with temperatures ranging from 0K to 1200K, as a means of analyzing the stability of each twin mode. The low-energy twins are selected for further calculation of electronic properties within density functional theory, using a plane wave basis and non-local pseudopotentials. In particular, the band structure and electron transport capabilities are computed. Focusing particularly on graphene, we show that twins can be systematically generated by applying deformations in preferred directions, allowing for manipulation of band gaps to advance the design of 2D materials.

3:30 PM Break

3:45 PM  Invited
Tailoring Properties of 2D Transition Metal Dichalcogenides: Looking Beyond Graphene: Talat Rahman1; 1University of Central Florida
    Single-layer of molybdenum disulfide (MoS2) and other transition metal dichalcogenides appear to be promising materials for next generation nanoscale applications (optoelectronic and catalysis), because of their low-dimensionality, intrinsic direct band-gap in the visible spectrum, and strikingly large binding energies for excitons and trions. MoS2 is also known to be a leading hydrodesulphurization catalyst. In this talk I will present results which provide a framework for manipulating the functionality of these materials and take us closer to the goal of rational material design. One emphasis will be on catalytic properties of pure and defect-laden single layer MoS2 with and without underlying support, and with adsorbed metallic nanoparticles. Another will be on the binding energies of multiple excitations (excitons, trions, biexcitons) in single and bilayer (hetero and homo) transition metal dichalcogenides. I will also discuss the characteristics of ultrafast charge dynamics in these systems, response to a short laser pulse. *Work supported by DOE grants DE-FG02-07ER15842 and DE-FG02-07ER46354.

4:15 PM  
Structural and Vibrational Properties of Transition Metal Dichalcogenide Polymorphs: Kamal Choudhary1; Arunima Singh1; Francesca Tavazza1; 1National Institute of Standards and Technology
    The polymorphs of the transition metal dichalcogenides (TMDCs) have attracted renewed research interest because of their rich as well as tunable physical and electrical properties. We compute the structural and vibrational properties of TMDCs (for example, bulk 2H, 1T’ and Td structures of MoTe2) with density functional theory using conventional LDA and PBE as well as van der Waals corrected optB88-vdW-DF functionals. The presented results show a strong functional dependent sensitivity in structural and vibrational properties for TMDCs. We compare the computed structural and vibrational properties with measurements in the literature and find that the dispersion corrected optB88-vdW-DF functional results in best agreement with measured values.

4:35 PM  Invited
Van der Waals Interactions in Nanoscale Materials: A Solved Problem ?: Alexandre Tkatchenko1; 1University of Luxembourg
    Van der Waals (vdW) interactions are ubiquitous in all materials. The influence of vdW forces extends beyond binding energies into the structural, mechanical, spectroscopic, and electronic signatures of condensed matter. Our conceptual understanding of these interactions is based on perturbative models, which are unable to capture the full extent of quantum-mechanical fluctuations which can extend up to tens of nanometers in real materials [1]. The origin of such many-body fluctuations will be discussed and their importance demonstrated for dimers, supramolecular complexes, semiconductors, to layered 2D heterostructures. The development of efficient many-body methods that explicitly address the collective nature of quantum fluctuations leads to significant improvements in the accuracy of calculations [2,3,4], and enables control of these fluctuations in the design of intricate materials. [1] Science 351, 1171 (2016). [2] Phys. Rev. Lett. 108, 236402 (2012). [3] Adv. Func. Mat. 25, 2054 (2015). [4] Chem. Sci. 6, 3289 (2015).

5:05 PM  
Two-Dimensional Materials-by-Design for Electronic and Energy Conversion Applications: Lan Li1; Izaak Williamson1; 1Boise State University
    To improve material properties, nanostructuring, doping or creating heterostruture are the common methods. Studies of those process influences offer an opportunity to explore new structure-property relationships and generate new materials. Two-dimensional transition metal dichalcogenides (2D-TMDs) are of interest due to novel electronic and thermoelectric properties. Having the chemical formula MX2, where M is a transition metal and X is a chalcogen, many combinations are possible. We applied economic and environmental criteria to narrow down from 62 to 18 potential compounds. We then implemented first-principles approach and Boltzmann transport theory, coupled with experiments, to screen electrical and thermal properties for 18 TMDs. Key factors were identified for desired performance. Substitutional doping and heterostructure effects were also explored. Atomic weight, radius, oxidation state and interfacial lattice mismatching control the properties. We will present a new and quick computational screening approach to identify new 2D materials for electronic and energy applications.

5:25 PM  
A Three-Dimensional Phase-Field Crystal Model for 2D Materials Using Multiple-Point Correlation Functions: David Montiel1; Guanglong Huang1; Matthew Seymour2; Nikolas Provatas2; Katsuyo Thornton1; 1University of Michigan; 2McGill University
    We introduce a Phase-Field Crystal (PFC) model that uses multiple-point correlation functions to simulate the growth of 2D materials in three dimensions. Our approach is based on the 2D model developed by Seymour and Provatas [Phys. Rev. E 93, 035447 (2016)], in which a three-point correlation term is used to energetically favor structures that feature specific bond angles. However, our PFC model also includes a four-point correlation term, which penalizes structural development in a direction perpendicular to a preferential plane, hence energetically favoring single-layer structures. We show how this model can be applied to study three-dimensional effects, such as buckling due to defect structures. This will allow us to examine how specific defects and grain boundaries affect growth and mechanical properties. Finally, we present examples of how our model can be adapted to study monolayers and multilayers, as well as the interaction of 2D materials with a substrate.