Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q31: Computational Nanoscience: Nanotubes and Graphene |
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Sponsoring Units: DMP DCOMP Chair: David Prendergast, Molecular Foundary, Lawrence Berkeley National Laboratory Room: Morial Convention Center 223 |
Wednesday, March 12, 2008 11:15AM - 11:27AM |
Q31.00001: Possible Precursors for Boron Nanotubes: A Novel Bonding Picture in Boron Sheets and Nanotubes Hui Tang, Sohrab Ismail-Beigi Boron nanotubes (BNTs) have attracted a great deal of attention due to their unique properties: unlike carbon nanotubes (CNTs), all BNTs are predicted to be metallic regardless of chirality or radii. Based on density functional theory, we present a class of boron sheets, composed of mixtures of triangular and hexagonal motifs, that are more stable than any sheet-structures considered to date and thus are more likely to be the precursors of atomically thin BNTs [1]. We describe a picture of the nature of the bonding in these sheets which clarifies their stability. We further point out that our bonding picture, which focuses on the balance of two-center and three-center bonding, is crucial for the stability of other boron nanostructures. We also discuss BNTs made from our new boron sheets. \newline [1] H. Tang and S. Ismail-Beigi, Phys. Rev. Lett. 99, 115501 (2007). [Preview Abstract] |
Wednesday, March 12, 2008 11:27AM - 11:39AM |
Q31.00002: Boron Nanotubes: Characterization Through Theory Abhishek Singh, Arta Sadrzadeh, Boris Yakobson Boron nanotubes have been believed to be metallic irrespective of diameter and chirality, as apposed to carbon nanotubes (CNTs), which could be both metallic and semiconducting. However, the separation of metallic and semiconducting CNTs is still a challenging task, which eventually, plagues their applications. Using first principle calculations, we investigate mechanical and electronic properties of the BNTs and show that BNTs could also be semiconducting. We discus the origin of semiconductivity in BNTs. Prospect of having only metallic BNTs is a great advantage over CNTs, however, having semiconducting BNTs could make them applicable in electronics, sensing and optoelectronics. [Preview Abstract] |
Wednesday, March 12, 2008 11:39AM - 11:51AM |
Q31.00003: On the Electronic and Geometric Structures of Armchair GeC Nanotubes: A Hybrid Density Functional Study Somilkumar Rathi, Asok Ray \textit{Ab initio} calculations within the framework of hybrid density functional theory and finite cluster approximation have been performed for the electronic and geometric structures of three different types of armchair germanium carbide nanotubes from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. A detailed comparison of the structures and stabilities of the three types of nanotubes will be presented. The dependence of the electronic band gaps on the respective tube diameters, energy density of states, dipole moments as well as Mulliken charge distributions have been investigated. Radial buckling of tube along with bond length variations is also studied. All armchair GeC nanotubes investigated so far are semiconducting in nature. Applications in the field of nano-optoelectronic devices, molecular electronics and band gap engineering are envisioned for GeC nanotubes. [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q31.00004: Water in nanoscale confinement: Insights into structure, dynamics, and $^{1}$H-NMR chemical shifts from first-principles theory Patrick Huang, Eric Schwegler, Giulia Galli The properties of water confined to nanoscale dimensions can differ markedly from bulk water. Numerous studies of confined water focus on water in carbon nanotubes (CNTs), because CNTs provide a uniform environment with a well-defined geometry and chemical composition. However, the behavior of water in CNTs remains controversial. Here, we apply first-principles density functional theory (DFT) to study the structure and dynamics of water in CNTs, and relate our microscopic picture to experimentally-accessible observables. One such observable is $^{1}$H-NMR, a sensitive probe of atomic-scale structure and dynamics. While empirical procedures to relate chemical shifts to structure are known for organic molecules, analysis of NMR spectra of solids and liquids requires more sophisticated approaches. We evaluate chemical shifts of water in CNTs within periodic DFT, and relate our findings to experimental $^{1}$H-NMR measurements. [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q31.00005: First-Principles Studies of Metal-Graphene and Metal-Nanotube Heterostructures Alejandro Lugo-Solis, Igor Vasiliev Metal-nanotube heterostructures have attracted considerable interest due to their potential applications in catalysis, fuel cell technology, and hydrogen storage. We investigate the optical properties of alkali metal atoms and clusters adsorbed on graphene and single-walled carbon nanotubes. The geometries, binding energies, and optical absorption spectra of the modeled structures are calculated in the framework of {\it ab initio} density-functional and time-dependent density-functional methods combined with the local-density approximation for the exchange-correlation functional. Our calculations show significant differences between the structures and absorption spectra of isolated alkali metal clusters and those adsorbed on graphene and carbon nanotubes. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q31.00006: Linear plasmon dispersion in graphene and single-wall carbon nanotubes and the influence of interlayer interactions R. Hambach, C. Giorgetti, F. Sottile, L. Reining, C. Kramberger, M.H. R{\"u}mmeli, M. Knupfer, J. Fink, B. B{\"u}chner, T. Pichler, E. Einarsson, S. Maruyama, K. Hannewald, V. Olevano, A.G. Marinopoulos Using first principles calculations [1], we studied momentum resolved electron energy loss spectra (EELS) for isolated graphene in RPA. In particular, we investigated the influence of interlayer interactions on the plasmon dispersion and the importance of local field effects (or depolarization effects). The latter cause a mixing of electronic transitions resulting in a nearly linear dispersion of the $\pi$-plasmon in graphene for in-plane momentum transfer. Corresponding EELS measurements on isolated, vertically aligned single-wall carbon nanotubes (SWCNT) show a very similar dispersion relation along the tube axis. This validates the use of graphene to understand electronic excitations of carbon nanotubes and vice versa. [1] www.dp-code.org [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q31.00007: Tuning Field-Induced Energy Gap of Bilayer Graphene via Interlayer Spacing Yufeng Guo, Wanlin Guo, Changfeng Chen Using first-principles calculations, we demonstrate a sensitive dependence of the electric-field-induced energy gap of bilayer graphene on its interlayer spacing. The calculated results reveal surprisingly large ($\pm$50\%) changes in the energy gap by relatively small ($\pm$10\%) adjustments in the interlayer spacing near the equilibrium structure when the electric field is sufficiently high (above 3 V/nm). We elucidate the underlying mechanism by examining the response of the interlayer charge distribution to the interlayer spacing variation at different electric fields. The present results suggest an effective way for reversible tuning of the field- induced energy gap of bilayer-graphene-based nanoelectronic devices through nanomechanical control. [Preview Abstract] |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q31.00008: Role of Surface Defects in the Carboxylation of Carbon Nanotubes: An \textit{Ab Initio} Study Nabil Al Aqtash, Igor Vasiliev We investigate the mechanism of covalent sidewall functionalization of carbon nanotubes with carboxyl groups using first principles computational methods. The binding energies and equilibrium geometries of carboxylated nanotubes with no surface defects, Stone-Wales defects and vacancies are calculated in the framework of density functional theory combined with the generalized gradient approximation. Our calculations show that the binding of carboxyl groups with carbon nanotubes containing surface defects is stronger than that with defect-free nanotubes. Furthermore, the presence of carboxyl groups on the surface leads to a considerable change of the electronic and structural properties of defective nanotubes. Our results suggest that surface defects play an important role in the formation of chemical bonds between chemical groups and carbon nanotubes. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q31.00009: An ab initio description of cleaning of SWNT with UV light Abram Van Der Geest, Kathrine Hurst, Mark T. Lusk The photodesorption of molecules and its application to the cleaning of single walled carbon nanotubes (SWNTs) has been experimentally demonstrated using a 248 nm laser. The excitation of the carbon nanotube $\pi$-plasmon is thought to couple to vibrational modes of the molecule-nanotube bond. An \it{ab initio}\normalfont \ inquiry seeks to validate this hypothesis and optimize the process of nanotube cleaning. The response of SWNTs to an electric field, a description of the enhancement of surface plasmons, and the role of hot electrons are discussed. [Preview Abstract] |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q31.00010: Modeling and simulation of adhesion between carbon nanotubes and surfaces Alper Buldum, Naba Raj Paudel, Toshiyuki Ohashi, Liming Dai There have been also many experimental studies which were performed to compare the adhesion properties of carbon nanotubes with that of a gecko's foot on smooth surfaces. Yurdumakan et al. measured the adhesive force of multiwalled carbon nanotube hairs and found it to be 200 times higher than that observed for gecko foot-hairs.Here, we present theoretical investigations of CNTs interacting with surfaces. We study the deformation of CNTs and evaluate their adhesion similar to the experimental investigation of a gecko's foot. To study the deformation behavior and adhesion of CNTs, atomistic simulations of capped armchair (10, 10) nanotubes with two different lengths are performed on rigid and relaxed graphite surfaces.Simulations were also performed for different orientations of the nanotube with respect to the graphite surface to study the angular dependence of adhesion and deformation. [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q31.00011: Monte Carlo simulations of the effect of nanotube length distribution on the percolation resistivity in single-walled carbon nanotube films Jeremy Hicks, Ashkan Behnam, Ant Ural Employing Monte Carlo simulations, we generate and calculate the resistivity of multilayer films made up of single-walled carbon nanotubes with various nanotube length distributions. Each layer in the film acts as a charge-percolating 2D mesh with contacts to adjacent layers. First, we study the case when the tube-tube contact resistance dominates the resistivity. For randomly oriented nanotubes, we find that, the resistivity of the film, as well as its overall percolation probability correlate strongly with the root mean square (RMS) length of the nanotubes near the percolation threshold regardless of distribution. As the nanotubes in the film become increasingly aligned, the resistivity correlation shifts to higher order in length. On the other hand, if the nanotube resistance dominates the resistivity, the resistivity of the film correlates strongly with the average nanotube length. These results, which can be explained by physical and geometrical arguments, show how individual nanotube parameters contribute to the macroscopic characteristics of the film. They also show that computational studies are an essential tool for providing insight into the percolation transport in single-walled carbon nanotube films. [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q31.00012: Mechanism for Superelongation of Carbon Nanotubes at High Temperature Chun Tang, Wanlin Guo, Changfeng Chen Recent discovery of superelongation of carbon nanotubes (CNTs) at high temperature raises fundamental questions about the deformation mechanism of these normally brittle materials. Here we report extensive molecular dynamics simulations that identify two key factors for this intriguing phenomenon: (1) activation of defects all over the tube at the elastic limit and continued emergence of additional defects at increasing strain that impede the formation of localized predominant instability and facilitate homogeneous deformation; (2) large-scale defect evolution that produces multistage necking and kink motion. Intricate interplay between CNT sizes and temperature activated defect nucleation and motion plays a key role in determining the overall deformation pattern. [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 1:51PM |
Q31.00013: Mesoscopic model for CNT-based materials Alexey Volkov, Kiril Simov, Leonid Zhigilei A mesoscopic computational model is developed for simulation of the collective mechanical and thermal behavior of carbon nanotubes (CNTs) in CNT-based materials. The model is based on a coarse-grained representation of CNTs as ``breathing flexible cylinders'' consisting of a variable number of segments. A novel effective ``tubular'' potential is developed for the description of van der Waals inter-tube interactions. It accounts for the relative local orientation of the interacting CNT segments. Frictional forces and energy dissipation, as well as heat conduction along and between CNTs, are incorporated into the mesoscopic model and parameterized with the help of results from atomistic simulations. The developed model is used in calculations of the mechanical and thermal properties of CNT meshes and mats. The systems under consideration contain thousands of CNTs, allowing for investigation of the effective properties of CNT-based materials. The computational results are related to available experimental data. [Preview Abstract] |
Wednesday, March 12, 2008 1:51PM - 2:03PM |
Q31.00014: First-principles studies of the switching performance of [2]rotaxane molecules and monolayers Kinyip Phoa, J.B. Neaton, Vivek Subramanian Density functional theory calculations of [2]rotaxane, an organic molecule consisting of a linear (straight) backbone and an encircling ring, which was recently proposed as the basis of a molecular memory device$^{[1]}$, are presented. The energy landscape describing the shuttling of the ring along the backbone is calculated and carefully investigated. Furthermore, to estimate the potential RC delays associated with this molecular memory circuit, the long-wave dielectric response of [2]rotaxane monolayers is explored by applying an external field. Our calculations shed new light on the underlying working principle of this system and build on previous studies$^{[2]}$. \newline [1] Y. Luo, et. al., ChemPhysChem, 3, 519-525, 2002 \newline [2] Y. H. Jang, et. al., J. Phys. Chem. B 110, 7660-7665, 2006 [Preview Abstract] |
Wednesday, March 12, 2008 2:03PM - 2:15PM |
Q31.00015: Structure-property relations in electronic switches based on the rotaxane and catenane supramolecular family Yong-Hoon Kim Mechanically interlocked bistable supramolecular complexes are promising candidates of molecular electronics. Applying a multiscale computational approach combining force-fields molecular mechanics, density-functional theory, and matrix Green's function calculations, we study the structure-property correlations in nanoelectronic switches based on [2]rotaxane and [2]catenane supramolecules. Computational aspects that increase the efficiency of charge transport characteristics calculations while ensuring the numerical accuracy will be also discussed. (This work was supported by the Korea Research Foundation Grant KRF-2007-331-C00077) [Preview Abstract] |
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