Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P27: Focus Session: Computational Nanoscience V - Nanotubes |
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Sponsoring Units: DMP DCOMP Chair: Rajendra Zope, University of Texas at El Paso Room: Colorado Convention Center 301 |
Wednesday, March 7, 2007 11:15AM - 11:27AM |
P27.00001: Absorption Coefficient for Cylindrical Nanotubes Godfrey Gumbs, Antonios Balassis A self-consistent field theory is presented for calculating the absorption coefficient for a pair of coaxial tubules. The spatially nonlocal dynamic formalism is obtained in terms of the electrostatic potential produced by the charge density fluctuations and the external electric field. There are peaks in the absorption spectrum arising from plasma excitations corresponding either to plasmon or particle-hole modes. We calculate numerically the plasmon contribution to the absorption. The number of peaks depends on the radius of the inner as well as outer tubule. The height of each peak depends on the plasmon wavelength and energy. For a chosen wavenumber, the most energetic plasmon has the highest peak corresponding to the largest oscillator strength. Some of the less energetic plasmon modes have such weak coupling to an external electric field that they are not seen on the same scale. We plot the peak positions of the plasmon excitations on a pair of coaxial tubules. The coupled modes on the two tubules are split by the Coulomb interaction. The energies of the two highest plasmon branches increase with the radius of the outer tubule. On the contrary, the lowest modes decrease in energy as this radius is increased. [Preview Abstract] |
Wednesday, March 7, 2007 11:27AM - 11:39AM |
P27.00002: Nanocables made of a transition metal wire and boron nitride Chih-Kai Yang, Jijun Zhao, Jianping Lu The boron nitride (BN) nanotube has a very wide band gap and can shield the nanowire encapsulated inside its cavity from outside interference. Our calculations indicate that transition metal wires can be inserted inside a variety of zigzag BN nanotubes exothermically. In particular a cobalt wire and the BN tube interact just like two giant molecules. The weak interaction between the BN tube and the wire ensures a low binding energy and a high magnetic moment that comes solely from the transition metals. High spin polarization at the Fermi level also indicates that the hybrid structure can be used as a nanocable for spintronic applications [Preview Abstract] |
Wednesday, March 7, 2007 11:39AM - 11:51AM |
P27.00003: {\it First principles} study of Crystalline Bundles of Single-Walled Boron Nanotubes Kah Chun Lau, Roberto Orlando, Ravindra Pandey {\it First principles} calculations based on density functional theory are performed to study the structural and electronic properties of the crystalline bundles of (n,0) zigzag-type single-walled boron nanotubes (SWBNT). The results predict a substantial modification in the properties of SWBNT bundles relative to those of the isolated nanotubes. The predicted modification can be attributed to a significant interplay between intra- and inter-tubular bonds in determining the stability of SWBNT bundles, analogous to the role played by intra- and inter-icosahedral bonds in the boron crystalline solids. The result shows the SWBNTs exhibit polymorphism, which is likely to be the cause of the difficulty in growing SWBNTs experimentally. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P27.00004: Dielectric Response and Born Dynamic Charge of BN Nanotubes from \textit{Ab Initio} Finite Electric Field Calculations Guang-Yu Guo, Shoji Ishibashi, Tomoyuki Tamura, Kiyoyuki Terakura Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima, carbon and other nanotubes have attracted considerable interest worldwide because of their unusual properties and also great potentials for technological applications. Though CNTs continue to attract great interest, other nanotubes such as BN nanotubes (BN-NTs) may offer different opportunities that CNTs cannot provide. In this contribution, we present the results of our recent systematic \textit{ab initio} calculations of the static dielectric constant, electric polarizability, Born dynamical charge, electrostriction coefficient and piezoelectric constant of BN-NTs using the latest crystalline finite electric field theory [1]. [1] I. Souza, J. Iniguez, and D. Vanderbilt, Phys. Rev. Lett. 89, 117602 (2002); P. Umari and A. Pasquarello, Phys. Rev. Lett. 89, 157602 (2002). [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P27.00005: First-Principles Study of Nucleic Acid Bases Physisorbed on Graphene S. Gowtham, R. H. Scheicher, Rajeev Ahuja, Ravindra Pandey, Shashi P. Karna We report the results of our investigation on the interaction of nucleic acid bases bases with graphene, carried out within the density functional theory framework, with additional calculations utilizing Hartree--Fock plus second--order M{\o}ller--Plesset perturbation theory. The calculated binding energy of the five nucleobases shows the following hierarchy: G $>$ T $\approx$ C $\approx$ A $>$ U, though the equilibrium configuration consists of nearly the same separation between the sheet and the bases considered. The stabilizing factor in the interaction between the nucleobases and the graphene sheet appears to be dominated by the molecular polarizability that induces a weakly attractive dispersion force between them. The present study is a first step toward understanding why different DNA sequences interact differently with CNTs, as observed experimentally. [Preview Abstract] |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P27.00006: The work function of small radius carbon nanotubes. Wan-Sheng Su, Tsan-Chuen Leung Carbon nanotubes workfunctions can deviate from that of graphene due to geometric and structural factors. We have systematically investigated the work functions of various forms of small radius carbon nanotubes and their derivatives by density functional calculations. We considered and compared the workfunctions of tubes and tube-bundles in order to understand the effects of chirality, tube-length and capping condition. Systematic trends are unraveled and discussed. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 12:39PM |
P27.00007: Work function of functionalized single-wall carbon nanotubes Nicholas Singh-Miller, Nicola Marzari Engineering the properties of carbon nanotubes is of fundamental importance for many of their practical applications; we focus here on the work function of metallic nanotubes, and on the changes that can be induced by electropositive or electronegative functionalizations. We study with density functional theory pristine, hydrogenated, and fluorinated (5,5) and (5,0) nanotubes along with more complex organic ligands as functional moieties, paying particular attention to the additional dipole interactions that can arise in periodic boundary conditions. Control of the Fermi level alignment is especially relevant for field-effect devices and for the Schottky barrier at carbon nanotube interfaces. [Preview Abstract] |
Wednesday, March 7, 2007 12:39PM - 12:51PM |
P27.00008: Continuum description of defects in carbon nanotubes Elif Ertekin, Daryl Chrzan Recently, indications of plastic deformation have been observed in carbon nanotubes: strain stiffening in nanotube torsional shafts and direct observations of kink motion to assist with elongation. These observations suggest the importance of defects, both their formation and dynamics, to nanotube mechanical properties. Remarkably, defect formation energies are not well--understood: formation energies of Stone--Wales defects (dislocation--like defects) vary by $\approx$ 3 eV, depending on the environment. Further, no attempt has been made to compute the total energies of dissociated Stone--Wales defects. To address these issues, we develop a continuum theory of defect formation in nanotubes based on the idea that the distortion field associated with the presence of a defect distribution is that which minimizes the elastic and curvature energies but is consistent with the topological constraints imposed by the defects. It makes no a priori assumptions about the defect strain fields, accounts for defect--defect interactions, and accomodates changes to the curvature and out--of--plane buckling. Formation energies of Stone--Wales defects in a wide variety of configurations are computed using total energy electronic structure methods and compared with the results of the continuum theory; the agreement is excellent, irrespective of defect arrangement. The result is an accurate and transferable continuum description of defect formation energies in carbon nanotubes. [Preview Abstract] |
Wednesday, March 7, 2007 12:51PM - 1:03PM |
P27.00009: Anharmonic phonon lifetimes in graphene, graphite and carbon nanotubes Nicola Bonini, Nicola Marzari, Michele Lazzeri, Francesco Mauri We present a density-functional study of anharmonic phonon lifetimes in low-dimensional graphitic structures. Phonon lifetimes are evaluated from the cubic terms in the interatomic potential, using density-functional perturbation theory and the 2n+1 theorem. We show that in graphene and graphite the phonon lifetimes of the $E_{2g}$ LO mode at {\bf $\Gamma$} and the ${A'}_1$ mode at {\bf K} due to phonon-phonon scattering are larger than those due to the electron-phonon interaction. We discuss the relevance of this finding for the transport properties and the implications for carbon nanotubes. We also present the results for the temperature-dependent frequency shift of the Raman G mode, in which third- and fourth-order anharmonic terms contribute equally. [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P27.00010: Electronic structures of MoS2 nanotubes. Lingyun Xu, Murray Daw, Xing Gao, Erdi Bleda The electronic structure of MoS2 nanotubes has been studied using first principles. We investigated MoS2 zigzag (n, 0) nanotubes as well as armchair (n, n) structure. We constructed MoS2 nanotube with ABA and ABC stacking. The structures have been completely optimized. We compare to previous tight-binding calculations by Seifert et al.(Phys. Rev. Lett. 85, 146 (2000)). [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P27.00011: The role of electron-phonon interactions and external strain on the~ electronic properties of semiconducting carbon nanotubes Denis Karaiskaj, Angelo Mascarenhas The electron-phonon interactions play an important role in the temperature dependent photoluminescence of semiconducting carbon nanotubes. The energy shifts and spectral narrowing of the excitonic transitions can both be attributed to the electron-phonon interaction. The thermal broadening was fitted by a theoretical expression previously used to model the thermal broadening of critical points in conventional semiconductors. Moreover, careful studies of the energy shifts induced by the external strain had revealed a (n-m) family behavior. We further conclude that using a mathematical expression that combines the theory of semiconducting carbon nanotubes under hydrostatic pressure and strain, this family behavior observed experimentally could be theoretically reproduced, providing new tools to model and predict the effect of strain on the electronic properties of carbon nanotubes. The temperature dependence of the photoluminescence decay of excitons in single walled carbon nanotubes was measured for two nanotube species, (7,6) and (7,5), representative of the two nanotube (n-m)mod3 families. The effect of temperature and external strain on the photoluminescence lifetime will be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P27.00012: Pi electron plasmon modes by the method of tight binding in an array of armchair single-walled carbon nanotubes. M. E. Markes, P. F. Williams P. R. Wallace introduced the method of tight binding in the study of graphene sheets about 50 years ago [1]. More recently, it has been possible to explain the relationship between the semiconductor/metallic behavior and carbon nanotube chirality by applying periodic axial boundary conditions to Wallace's band model [2]. Several years ago one of us (P. F. Williams [3]) developed a self-consistent dielectric response model for arrays of one-dimensional metal filaments using a tight-binding approximation. At the time this model was found useful in a study of the single-particle excitations and plasmon dispersion curves of tetrathiofulvalene-tetracyano-quinodimethane (TTF-TCNQ). This paper is a report of work in progress to extend the Williams-Bloch model to arrays of single-walled carbon nanotubes modeled using the Wallace tight-binding model and axial periodic boundary conditions. The collective excitations are characterized by a frequency and wavelength dependent dielectric function obtained using a self-consistent field in the random phase approximation. The zeros of this function yield the plasmon modes. [1] P. R. Wallace, Phys. Rev., vol. 71, 1947. [2] R. Saito et. al., Appl. Phys. Lett., vol. 60, 1992. [3] P. F. Williams and A. N. Bloch, Phys. Rev. B, vol. 10, 1974. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P27.00013: Electronic structure of Defective and Deformed Single Wall Carbon Nanotubes L.M. Woods, Ya. Shtogun, T.L. Reinecke Carbon nanotube properties can be modified by the introduction of defects on their surface or by mechanical deformations. Here we present an alternative way to modify carbon nanotube characteristics by considering both types of mechanical alterations, defects and deformations, on the nanotube surface. Electronic structure calculations from first principle density functuional theory using the VASP code (Viena Ab initio Simulations Package) for metallic and semiconducting single walled carbon nanotubes with Stone-Wales defect and radial deformation are presented. The difrferent degrees of deformation and various defect locations are analyzed in terms of the density of states and bandstructures of these systems. We compare the defective and deformed nanotube electronic structure to the electronic structure of only defective or only deformed nanotubes. In this way we determine the relative importance of the two types of mechanical alterations on the defective and deformed nanotubes. [Preview Abstract] |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P27.00014: Electron-phonon coupling mechanism, Kohn anomalies and Peierls instabilities in two-dimensional graphite and single-wall carbon nanotubes Georgy Samsonidze, Eduardo Barros, Riichiro Saito, Hyungbin Son, Gene Dresselhaus, Mildred Dresselhaus The electron-phonon coupling in two-dimensional graphite and metallic single-wall carbon nanotubes (SWNTs) is analyzed. The $G'$-band phonon mode opens a dynamical band gap that induces a Kohn anomaly in two-dimensional graphite, while truly metallic armchair SWNTs undergo Peierls transitions driven by the $G$- and $G'$-band phonon modes. The dynamical band gap induces a non-linear dependence of the phonon frequencies on the doping level and gives rise to strong anharmonic effects. [Preview Abstract] |
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