Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q16: Focus Session: van der Waals Bonding in Advanced Materials: Nano-Materials |
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Sponsoring Units: DMP Chair: Alexandre Tkatchenko, Fritz Haber Institute of the Max Planck Society Room: 101AB |
Wednesday, March 4, 2015 2:30PM - 3:06PM |
Q16.00001: Beller Lectureship: Van der Waals interactions in adhesion, adsorption and friction experiments Invited Speaker: Karin Jacobs Van der Waals (vdW) forces are commonly regarded as being weak and of short range and are thus often neglected. However, our experiments give clear evidence that vdW forces significantly contribute to a range of phenomena at interfaces, like thin film stability, protein adsorption, bacterial and gecko adhesion as well as single asperity friction [1-5] and that vdW forces can be of long range. The key for an apt description of vdW and further relevant forces present in these diverse system is a precise knowledge about the interacting objects, for instance their chemical composition from the surface up to roughly 100 nm into the bulk. The effective interface potentials used to describe and understand the different experimental situations can additionally serve as useful descriptions for future simulations of similar systems, which will gain in precision and predictive power when taking vdW interactions into account.\\[4pt] [1] P. Loskill et al., Adv. Coll. Interf. Sci. 107 (2012) 179182;\\[0pt] [2] H. H\"ahl et al., Langmuir 28 (2012)~7747;\\[0pt] [3] P. Loskill et al., Langmuir 28 (2012) 7242;\\[0pt] [4] P. Loskill, J. R. Soc. Interface 10 (2013) 20120587;\\[0pt] [5] M. Lessel et al., Phys. Rev. Lett. 111 (2013) 035502. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q16.00002: Van derWaals-coupled electronic states in incommensurate double-walled carbon nanotubes Chenhao Jin, Kaihui Liu, Xiaoping Hong, Jihoon Kim, Alex Zettle, Enge Wang, Feng Wang In two-dimensional materials consisting of elements without finite unit cell, such as twisted graphene bilayer or graphene on boron nitride, the incommensurate van der Waals coupling can give rise to emerging physics like Van Hove singularities, pseudospin-mixing potential and Hofstadter butterflies. However, their 1D counterpart, incommensurate double-walled carbon nanotube (DWNT), is conventionally believed to have negligible electron hybridization due to destructive interference. Here we for the first time demonstrate strong and chirality-dependent intertube electronic coupling in DWNTs, which can be well described by a zone folding model of twisted and ``stretched'' graphene bilayers. Our results demonstrate that incommensurate van der Waals interactions can be important for engineering the electronic structure and optical properties of one-dimensional materials. [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q16.00003: Double-walled carbon nanotubes as one-dimensional moir\'{e} crystals Pilkyung Moon, Mikito Koshino, Young-Woo Son Being multi-shell structure, the well-defined atomic periodicity is hardly realizable in double-walled nanotubes because the periodic units of individual tubes therein cannot match well except very few cases, posing a challenge to understand its physical properties. Here we show that moir\'{e} patterns generated by superimposing atomic lattices of individual tubes are decisive in determining its electronic structures [1]. By using double-walled carbon nanotubes as an example, we demonstrate that even the combination of semiconducting nanotubes with almost the same physical properties such as diameter and energy gap can end up with very different double-walled nanotubes, of which electronic properties vary from metallic to semiconducting and further to insulating states, depending on the interlayer moir\'{e} interference. Our study puts forth a new classification of nanotubes as the first example of one-dimensional moir\'{e} crystals and paves a firm ground to utilize superb technological merits of double-walled carbon nanotubes. [1] Mikito Koshino, Pilkyung Moon, and Young-Woo Son, arXiv:1410.7544 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q16.00004: Dynamical Screening of van der Waals interactions in nanostructures: Sublimation of fullerenes Andrew M. Rappe, Jianmin Tao, Jing Yang Sublimation energy is one of the most important properties of molecular crystals, but it is difficulty to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. In this talk, I will discuss our recent work on the calculation of the sublimation of fullerenes, using efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT+vdW), the Langreth-Lundqvist nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction. On the other hand, higher-order contributions can be as important as the leading-order term. However, these two effects make opposite contributions, leading to significant error cancellation. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT+vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for better understanding of the long-range nature [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q16.00005: van der Waals density functional comparison for water monomers, dimers and clusters and the implications on the dynamics of liquid water Adrian Soto, Marivi Fernandez-Serra, Deyu Lu The appearance of van der Waals (vdW) density functionals has allowed the efficient ab initio molecular dynamics (AIMD) study of systems for which dispersion forces are critical. Despite the great improvement over GGA functionals, the errors in the simulations are still too large for some applications of interest. Furthermore, different vdW functionals can produce qualitatively different results. In particular, for liquid water at ambient conditions there is a discrepancy of approximately $20\%$ in the yielded $P(\rho)$ ``equations of state"; the radial distribution functions (RDF) disagree substantially with experiment, giving an overstructured liquid mainly due to an overbinding of the hydrogen bond; the self-diffusion coefficients can vary over $75\%$ [J. Chem Phys. 139, 194502(2013)]. In this study we focus on the role of the electronic polarizabilities, responsible for the vdW dispersion forces using two very different vdW functionals. In particular we study how 1-body, 2-body and 3-body terms modify the molecular polarizabilities and how these effects are linked to the many-body decomposition of the total energy of the systems. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q16.00006: Van der Waals Coefficients between Clusters or Fullerenes: A Simple but Accurate Model beyond the Atom-Pair Interaction Picture John P. Perdew, Adrienn Ruzsinszky, Jianmin Tao The van der Waals coefficients of all orders between two spherical objects may be computed from the dynamical multipole polarizabilities of the two objects via the Casimir-Polder formula. We present an analytic model [1] for the dynamical polarizabilities that is exact for a classical conducting sphere or spherical shell, exact in the zero- and nearly-exact in the high-frequency limits, and generally accurate. From this model, we compute the low-order van der Waals coefficients for a variety of atom pairs and pairs of clusters or carbon-based fullerenes. We find that the lowest-order coefficient C6 per atom pair may increase or decrease strongly with cluster size, signaling a failure of the simplest version of the atom-pair interaction picture. [1] J. Tao and J.P. Perdew, J. Chem. Phys. 141, 141101 (Commun.) (2014). [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q16.00007: Van der Waal's corrected linear-scaling Density Functional Theory investigation of inner-surface functionalized inorganic nanotubes Joshua Elliott, Gilberto Teobaldi We report a linear-scaling Density Functional Theory investigation of single-walled open-ended aluminosilicate nanotubes with inner methyl functionalization (AlSiMe NTs). In line with the experimental pore-size distributions,\footnote{\textbf{Phys. Chem. Chem. Phys.}, 13, 744(2011)} optimization of the AlSiMe NT structure with six different semi-local and non-local van der Waals DFT functionals suggests the presence of a shallow energy-minimum for NTs with 28 to 32 Al-atoms in the NT circumference, resulting in larger diameter than for aluminosilicate (AlSi) NTs. Analysis of the AlSiMe NTs electronic structure reveals the wall-polarization and real-space separation between Valence Band and Conduction Band, characteristic of AlSi NTs.\footnote{\textbf{J. Phys. Condens. Mat.}, 21, 195301(2009)} Regardless of the functional, the wall of the AlSiMe NTs are however found to be less polarized than AlSi NTs, with NTs of larger diameter being more polarized. We quantify the effect of the AlSiMe NTs wall-polarization and polarizability on the absolute alignment of the states for adsorbed H$_2$O molecules inside and outside the tube-cavity. The simulations indicate shifts as large as 2 eV between the H$_2$O-states for molecules adsorbed inside and outside the NT-cavity. [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q16.00008: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q16.00009: Water Dissociation Mechanism in MOF-74 Sebastian Zuluaga, Kui Tan, Pieremanuele Canepa, Yves Chabal, Timo Thonhauser Water dissociation represents one of the most important reactions in catalysis, essential to surface and nano sciences. Combining in-situ IR spectroscopy and first-principles calculations, we demonstrate, for the first time, that water starts to dissociate at the metal centers of MOF-74 at temperatures as low as 150~$^{\circ}$C. The fingerprint of this reaction is a sharp band in the IR spectrum at 970~cm$^{-1}$ when D$_2$O is introduced into the MOF. Surprisingly, this fingerprint is not detected by experiments with H$_2$O. To explain this peculiar finding, we perform DFT simulations of the reaction, utilizing vdW-DF to capture the important van der Waals interactions. Our calculations show that, once the D$_2$O molecule is adsorbed at the metal center, the D atom is transferred to the oxygens of the linker (phenolate group), producing the notable O-D absorption band at 970~cm$^{-1}$, while the OD remains at the open metal sites. Even though we find that H$_2$O undergoes an analogous dissociation reaction, the corresponding O-H mode is strongly coupled to MOF vibrations and cannot easily be detected by experiments. Overall, this work elucidates water interactions with cation-exposed surfaces and aids in the development of more efficient catalysts for water dissociation. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q16.00010: Distortion of a liquid crystal bulk by the Casimir torque David Somers, Jeremy Munday We present an experimental method for measuring the Casimir torque acting on liquid crystals from a birefringent crystal. A liquid crystal bulk that is uniformly aligned at one surface is twisted at the other surface by a crystal such as barium titanate. The liquid crystal is separated from the solid crystal by an isotropic, transparent material such as SiO$_{2}$. By varying the thickness of the deposited layer, we can observe the effect of retardation on the torque (which differentiates it from the close-range van der Waals torque) and compare experimental results to dispersion data of the materials. We find that a barium titanate slab could cause 5CB liquid crystal to rotate by 10 degrees through its bulk, even when separated by 35 nm of SiO$_{2}$. The optical technique for measuring this distortion is also outlined. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q16.00011: Casimir-like Forces via Charge Fluctuations David Drosdoff, Igor Bondarev, Lilia Woods Fluctuations of observables give rise to different forces. Dipolar fluctuations have been studied extensively for a variety of systems as they give rise to Casimir (finite speed of light) and van der Waals (infinite speed of light) interactions. Charge fluctuations can also be responsible for Casimir-like forces with particular importance in biological systems. We show that such phenomena are also of relevance to capacitor systems especially when nanostructured materials are involved. We present a theory with a novel view of charge fluctuations induced interactions via the quantum capacitance concept. It is demonstrated that such Casimir-like forces can be important, especially in nanostructures. The theory is applied to nanoscale capacitors involving graphene and other characteristic materials. [Preview Abstract] |
Wednesday, March 4, 2015 5:06PM - 5:18PM |
Q16.00012: Measurement of Casimir forces with nonmonotonic distance dependence between silicon structures with non-conventional shapes Lu Tang, Jie Zou, Ho Bun Chan, Milos Nikolic, Alejandro Rodriguez We measure the Casimir force between silicon components of non-conventional shapes on a silicon-on-insulator wafer. The device consists of a force-sensing micromechanical beam and a comb-drive actuator for controlling the distance. The magneto-motive technique is used to measure the shift in the resonance frequency of the force sensing beam. Each of the interacting surfaces contains an array of T-shaped protusions. Since the protusions on both sides are created by lithography and reactive ion etching, both their shapes and relative positions can be accurately defined. Here, the protusions on the two surfaces are offset by half the period. As the movable electrode is pushed towards the silicon beam by the comb drives, the two sets of protusions inter-penetrate. The lateral Casimir force between the top parts of the T-shaped structures produces in an overall interaction that is either apparently attractive or repulsive depending on the displacement of the comb actuators. The measured non-monotonic dependence of the Casimir force on distance is in qualitative agreement with preliminary calculations using the boundary elements method. [Preview Abstract] |
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