Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L31: Focus Session: Computational Discovery and Design of New Materials III |
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Sponsoring Units: DMP DCOMP Chair: Hongjun Xiang, Fudan University Room: 607 |
Wednesday, March 5, 2014 8:00AM - 8:12AM |
L31.00001: Mechanical and electronic properties of pristine and Ni-doped Si, Ge, and Sn sheets Aaditya Manjanath, Vijay Kumar, Abhishek Singh Silicene, a graphene analogue of silicon, has been generating immense interest due to its potential for applications in miniaturized devices. Unlike planar graphene, silicene prefers a buckled structure. Here we explore the possibility of stabilizing a planar form of silicene by Ni doping using first principles density functional theory based calculations. It is found that planar as well as buckled structure is stable for the Ni doped silicene, but the buckled sheet has slightly lower total energy. The planar silicene sheet has unstable phonon modes. A comparative study of the mechanical properties reveals that the in-plane stiffness of both the pristine and the doped planar silicene is higher compared to that of the buckled silicene. This suggests that planar silicene is mechanically more robust. Electronic structure calculations of the planar and buckled Ni-doped silicene show that the energy bands at the Dirac point transform from linear behavior to parabolic dispersion. Furthermore, we extend our study to Ge and Sn sheets that are also stable and the trends of comparable mechanical stability of the planar and buckled phases remain the same. [Preview Abstract] |
Wednesday, March 5, 2014 8:12AM - 8:24AM |
L31.00002: Single-layer honeycomb like structure of silica Seymur Cahangirov, V. Ongun Ozcelik, Salim Ciraci Silica or SiO$_2$, the main constituent of earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphite like layered structure in 3D. Our theoretical analysis and numerical calculations from the first-principles predict that silica can have stable, suspended, single-layer honeycomb like allotrope, h$\alpha$-silica (silicatene), which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with re-entrant angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under external electric field. In particular, it is an auxetic nanomaterial with negative Poisson's ratio and has high piezoelectric coefficient. Coverage of foreign adatoms can attribute new functionalities to h$\alpha$-silica such that by oxidation it turns into to a wide band gap insulator like the parent quartz. [Preview Abstract] |
Wednesday, March 5, 2014 8:24AM - 8:36AM |
L31.00003: First-principles prediction of the structural, electronic and vibrational properties for t-silicene Eduardo Cifuentes-Quintal, Romeo de Coss With the synthesis of graphene and the discovery of its amazing properties, the research and the design for new 2D-materials began. In this line, silicene (silicon analogous to graphene) becomes very attractive because most of the current technology is already based on silicon. Therefore, the discovery of new silicon based 2D-materials with different properties could be helpful. In this work we have studied the vibrational stability for a new two-dimensional silicon allotrope based on buckled tetrarings (T-silicene). Our results were obtained within the framework of the density functional perturbation theory, using the plane-wave pseudopotential method, and the GGA-PBE96 exchange-correlation functional. We found that, in analogy to hexagonal Silicene, plane and buckled T-silicene are energetically stables. However, plane T-silicene shows imaginary phonon frequencies, and therefore is vibrationally unstable. Thus, buckled T-silicene is vibrationally stable and presents metallic character. More interestingly, the electronic structure shows that the energy bands crossing the Fermi level have a linear behavior with the wave vector. We will present a detailed analysis of this feature. [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 9:12AM |
L31.00004: Computational discovery of new structures using the minima hopping method Invited Speaker: Stefan Goedecker Theoretical structure prediction methods can find a huge number of possible low energy structures of materials. I will present some basic principles for locating them efficiently and show how these principles are exploited in the minima hopping method. I will next survey some of our applications to various materials. I will present our studies of several hydrogen storage materials for which we found numerous hitherto unknown structures, computer generated silicon allotropes that have promising applications for photovoltaic applications and summarize our search for stable fullerene like structures beyond carbon. I will also address the question of whether theoretically found materials can be synthesized in practice and single out features of the potential energy landscape that facilitate the synthesis. [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L31.00005: Novel Be-intercalated Hexagonal Boron Layers Structure of BeB2 Kai-Ming Ho, Manh Cuong Nguyen, Xin Zhao, Cai-Zhuang Wang Using genetic algorithm method and first-principle calculations, we performed searches for low-energy crystal structures of BeB2. We found a new family of structures, where the B atoms form hexagonal layers intercalated by Be atoms. The lowest-energy structure has formation energy of -99.47 meV/atom with 4 formula units in the unit cell, which is much more stable than the models proposed before. The formation energies of structures in the new structure family can be well described by a Ising-like model with ``anti-ferromagnetic'' coupling between the displacements of Be atoms from the mid-plane between two B layers. We also performed phonon calculation as well as electronic band structure calculation to verify the stability and investigate the electronic properties of the newly found ground-state structure. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L31.00006: Prediction of a reconstructed $\alpha$-boron (111) surface by the minima hopping method Maximilian Amsler, Stefan Goedecker, Silvana Botti, Miguel A.L. Marques Boron exhibits an impressive structural variety and immense efforts have recently been made to explore boron structures of low dimensionality, such as boron fullerenes, two-dimensional boron sheets or boron nanotubes which are theoretically predicted to exhibit superior electronic properties compared to their carbon analogues. By performing an extensive and systematic \textit{ab initio} structural search for the (111) surface of $\alpha$-boron (111) using the minima hopping structure prediction method we found very strong reconstructions that lead to two-dimensional surface layers. The topmost layer of these low energy reconstructions is a conductive, nearly perfectly planar boron sheet. If exfoliation was experimentally possible, promising precursors for a large variety of boron nano-structures such as single walled boron nanotubes and boron fullerenes could be obtained. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L31.00007: The ferromagnetic properties of MnX2 Monolayers Qiang Sun Since the successful synthesis of graphene, tremendous efforts have been devoted to two-dimensional monolayers such as boron nitride (BN), silicene and MoS2. These 2D materials exhibit a large variety of physical and chemical properties, but they are intrinsically nonmagnetic in their pristine forms. In order to explore the applications in spin-related devices, considerable efforts have been made to study ferromagnetic monolayers. We have systematically studied the electronic and magnetic properties of the MnX2 (X$=$O, S, Se) monolayers, and found that they display intrinsic ferromagnetism with high Curie temperatures.. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L31.00008: Aligning the band edges of Si surfaces with water redox potentials: a first-principles study Eric Schwegler, Tuan Anh Pham, Donghwa Lee, Giulia Galli We present first-principles calculations of the alignment between the band edges of several Si surfaces with water redox potentials using many-body perturbation theory, coupled with \textit{ab initio} molecular dynamics simulations. Our results show that surface functionalization strongly influences the electronic properties of the interface, and indicate that a favourable alignment of band edges and water redox potentials for water splitting applications may be achieved by engineering the surface termination of the Si-based photo-electrodes. In addition, we found that in the case of hydrophilic Si surfaces, the use of simple computational schemes that neglect the detailed microscopic structure of the interfacial water layer may lead to substantial errors in predicting the alignment between the solid band edges and water redox potentials. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L31.00009: Stability and Electronic Properties of Two-Dimensional Silicene and Germanene on Graphene Chih-Piao Chuu, Yongmao Cai, C.-M. Wei, M.-Y. Chou Recently, there have been experimental attempts to synthesize silicene, a two-dimensional (2D) graphene-like form of silicon on metal surfaces such as Ag(111) and Ir(0001). The possibility of preparing silicene on ZrB2 thin films grown on silicon wafers has also been reported. This suggests new perspectives for the applications of massless fermions in materials that are compatible with Si-based electronics. It is expected that many of the unique electronic properties of graphene can also be realized in this new 2D system. However, the interaction between the 2D silicon structure and the metal substrate is found to be quite strong, leading to distortion in the adlayer and consequently the disappearance of the Dirac cone. Therefore, finding a suitable substrate that interacts with silicene weakly and preserves the sublattice symmetry is of ultimate importance. We have performed first-principles calculations of silicene and germanene on graphene in order to understand the effect of substrate interaction on the physical properties of these systems. Of particular interest is the induced change in the electronic structure, the modification of the Fermi velocity, the gap opening, the charge doping from the substrate, and the stability of the combined system. The energetics of forming the 2D silicone structure on a substrate is carefully evaluated in comparison with possible three-dimensional cluster structures. [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L31.00010: Prediction of novel single-layer materials for device applications Benjamin C. Revard, William W. Tipton, Richard G. Hennig Single-layer materials represent a new materials class with potentially transformative properties for applications in nanoelectronics and solar energy harvesting. With the goal to discover novel 2D materials with unusual compositions and structures, we have developed a grand-canonical evolutionary algorithm for two-dimensional materials. Here we present the details of the algorithm and our initial results. Using both empirical and first principles total energy methods in the evolutionary algorithm, we show that the method can successfully identify known structures of 2D materials such as graphene and graphane. We currently apply the approach to a number of other promising candidate systems and will report the findings. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L31.00011: A molecular dynamics study on the structural and electronic properties of two-dimensional icosahedral B12 cluster based structures Cherno Baba Kah, M. Yu, C.S. Jayanthi, S.Y. Wu Our previous study on one-dimensional icosahedral B12 cluster ($\alpha $-B12) based chain [Bulletin of APS Annual Meeting, p265 (2013)] and ring structures has prompted us to study the two-dimensional (2D) $\alpha $-B12 based structures. Recently, we have carried out a systematic molecular dynamics study on the structural stabilities and electronic properties of the 2D $\alpha $-B12 based structures using the SCED-LCAO method [PRB 74, 15540 (2006)]. We have considered several types of symmetry for these 2D structures such as $\delta $3, $\delta $4, $\delta $6 (flat triangular), and $\alpha $' types. We have found that the optimized structures are energetically in the order of $\delta $6 \textless $\alpha $' \textless $\delta $3 \textless $\delta$4 which is different from the energy order of $\alpha $'\textless $\delta $6 \textless $\delta $4 \textless $\delta $3 found in the 2D boron monolayer sheets [ACS Nano 6, 7443 (2012)]. A detailed discussion of this study will be presented. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L31.00012: Temperature Effects on Optical Spectra of Monolayer MoS2 Li Yang We present the effects of temperature on the electronic structure and optical spectra of monolayer MoS2. Newly measured optical absorption and photoluminescence spectra reveal substantial frequency shifts of exciton peaks as monolayer MoS2 is cooled from 300 K to 4 K. First-principles simulations using the GW-Bethe Salpeter Equation approach satisfactorily reproduce these frequency shifts by incorporating the thermal expansion. Studying these temperature effects in monolayer MoS2 is crucial for rectifying the results of room-temperature experiments with the previous predictions of zero-temperature-limit simulations. Additionally, we show that tracking the frequency shifts in the exciton peak of optical spectra may serve as a convenient way of estimating thermal expansion coefficients in two-dimensional chalcogenides. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L31.00013: Magnetization and magnetic anisotropy of 3d adatoms on a MoS$_{2}$ monolayer Marcio Costa, Jun Hu, Ruqian Wu MoS$_{2}$ is layered semiconductor that goes under a transition from indirect (bulk - 1.2 eV) to a direct (monolayer - 1.8 eV) gap. MoS$_{2}$ monolayer has been drawing attention due to its peculiar transport properties, with mobilities of 200 cm$^{2}$ V$^{-1}$ s$^{-1}$ at room temperature. Using Density Functional Calculations, we studied the adsorption of transition metal adatoms on the MoS$_{2}$ monolayer. The adsorption energies of Mn, Fe, Co and Ni on MoS2 monolayer were calculated over different sites. We also determined their magneto crystalline anisotropy (MCA) energies, for the purpose of using these systems in spintronic devices. To manipulate the magnetic properties, the effect of coadsorption of Bi and other elements were also investigated. [Preview Abstract] |
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