Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D31: Focus Session: Van der Waals Interactions in Complex Materials: Bridging Theory and Experiment I |
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Sponsoring Units: DMP Chair: Alexandre Tkatchenko, Fritz Haber Institute, Germany Room: 607 |
Monday, March 3, 2014 2:30PM - 3:06PM |
D31.00001: Modern theory of van der Waals interactions Invited Speaker: John Dobson van der Waals (vdW, dispersion) interactions [1,2,3] are important in diverse areas such as colloid, surface and nano science, cohesion of molecular crystals, and biomolecular science. They also provide competition in experiments to discover the fifth fundamental force.While vdW interactions have been understood in principle for a century, their quantitative first-principles prediction and modelling down to chemical contact separations have proven stubbornly difficult because the quantal many-electron problem is involved. After some brief historical material, the current state of the art will be discussed with particular reference to several approaches: pairwise additive [4,5,6], perturbative [7,8] quantum chemical [9], vdW-DF [10,11], Lifshitz-like scattering[1,2,12], RPA-like [13-17], Adiabatic Connection Fluctuation Dissipation / Time Dependent DFT based [18,19] etc.. A potentially useful classification will be introduced to aid in understanding the physical causes of departures from pairwise additivity, that is from the usual sum of $C_6 R^{-6}$ contributions. These departures result in non-standard power law decays of nanostructure vdW interactions as a function of separation $D$ [13], as well as surprising dependences of the attraction on the number, $N$, of atoms within each vdW-interacting fragment [20,21]. Some further recent results on non-additivity will also be presented [22]. REFERENCES. [1] V. A. Parsegian, ``van der Waals Forces,'' Cambridge University Press, Cambridge 2005: [2] J. F. Dobson and T. Gould, J. Phys. Condens. Matter 24, 073201 (2012): [3] J. Klimes \& A. Michaelides, J. Chem. Phys. 137, 120901 (2012) : [4] S. Grimme, J. Antony, S. Ehrlich, et al., J. Chem. Phys. 132, 154104 (2010): [5] S. Ehrlich, J. Moellmann, and S. Grimme, Acc. Chem. Research 46, 916 (2013): [6] R. Sedlak, T. Janowski, M. Pitonak et al., J. Chem. Th. Comput. 9, 3364 (2013): [7] B. Jeziorski, R. Moszynski, and K. Szalewicz, Chem. Rev. 94, 1887 (1994): [8] D. Kuchenbecker and G. Jansen, Chem. Phys. Chem. 13, 2769 (2012): [9] J. Rezac, L. Simova, and P. Hobza, J. Chem. Th. Comput. 9, 364 (2013): [10] M. Dion, H. Rydberg, E. Schroder, et al., Phys. Rev. Lett. 92, 246401 (2004): [11] K. Berland and P. Hyldgaard, Phys Rev B 87, 205421 (2013): [12] S. J. Rahi, T. Emig, N. Graham, et al., Phys. Rev. D 80, 085021 (2009): [13] J. F. Dobson, A. White and A. Rubio, Phys. Rev. Lett. 96, 073201 (2006): [14] S. Lebegue, J. Harl, T. Gould, et al., Phys. Rev. Lett. 105, 196401 (2010): [15] A. Tkatchenko, R. di Stasio, R. Car, et al., Phys. Rev. Lett. 108, 236402 (2012): [16] T. Bucko, S. Lebegue, J. Hafner, J. G. Angyan, Phys. Rev. B. 87, 064110 (2013): [17] A. Gruneis, J. Harl, M. Marsman, et al., J. Chem. Phys. 131, 154115 (2009): [18] T. Gould, J. Chem. Phys. 137, 111101 (2012): [19] T. Olsen and K. Thygesen, Phys. Rev. B 88, 115131 (2013): [20] A. Ruzsinszky, J. P. Perdew, J. Tao et al., Phys. Rev. Lett. 109, 233203 (2012): [21] V. V. Gobre and A. Tkatchenko, Nature Comm. 4, 2341 (2013): [22] J. F. Dobson, A. Savin, J.A. Angyan, and R.F. Liu, unpublished. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D31.00002: Van der Waals Forces in Quasi 1-D Structures David Drosdoff, Lilia Woods Analytical formulations of Van der Waals-Casimir forces in terms of the macroscopic response of the system have been done extensively for 2-D and 3-D systems. On the other hand, quasi 1-D materials have been studied less, in part because of the difficulty in solving the boundary conditions. In this talk, by using the RPA method, we present a formulation of the Van der Waals force in narrow infinitely long ribbons. This approach is applied in the quantum mechanical and thermal regimes to several typical systems, such as insulators, metals, and semiconductors. Novel results are found for graphene nanoribbons, for which a transition from quantum mechanical to thermal van der Waals force can be realized at room temperature by changing the chemical potential. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D31.00003: Van der Waals forces and electron-electron interactions in two strained graphene layers Anand Sharma, Peter Harnish, Alexander Sylvester, Valeri N. Kotov We evaluate the van der Waals (vdW) interaction energy at T=0 between two undoped graphene layers which are separated by a finite distance. Our study is carried out within the Random Phase Approximation and the interaction energy is obtained for variation in the strength of effective Coulomb interaction and anisotropy due to applied uniaxial strain. We consider the following three models for the anisotropic case: a) where one of the two layers is uniaxially strained, b) the two layers are strained in the same direction, and c) one of the layers is strained in the perpendicular direction. We find that for all the three models and any given value of the coupling, the vdW interaction energy increases with increasing anisotropy. The effect is most striking for the case when both the layers are strained in the parallel direction where we observe up to an order of magnitude increase in the strained graphene relative to the unstrained case. We also investigate the effect of intra-layer electron-electron interactions in the region of large separation between the strained graphene layers. We conclude that the many-body contributions to the correlation energy are non-negligible and the vdW interaction energy decreases as a function of increasing distance between the layers. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D31.00004: Observation of Pull-in Instability in Graphene Membranes under Interfacial Forces Xinghui Liu, Narasimha Boddeti, Mariah Szpunar, Luda Wang, Miguel Rodriguez, Rong Long, Jianliang Xiao, Martin Dunn, Scott Bunch We present a unique experimental configuration that allows us to determine the interfacial forces on nearly parallel plates made from single and few layer graphene membranes. Our approach consists of using a pressure difference across a graphene membrane to bring the membrane to within $\sim$ 10-20 nm above a circular post covered with SiO$_{x}$ or Au until a critical point is reached whereby the membrane snaps into adhesive contact with the post. Continuous measurements of the deforming membrane with an AFM coupled with a theoretical model allow us to deduce the magnitude of the interfacial forces between graphene and SiO$_{x}$ and graphene and Au. The nature of the interfacial forces at $\sim$ 10 - 20 nm separations is consistent with an inverse fourth power distance dependence, implying that the interfacial forces are dominated by van der Waals interactions. Furthermore, the strength of the interactions is found to increase linearly with the number of graphene layers. The experimental approach can be applied to measure the strength of the interfacial forces for other emerging atomically thin two-dimensional materials. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D31.00005: How many-body effects modify the van der Waals interaction between graphene sheets John Dobson, Tim Gould, Giovanni Vignale Cold undoped graphene sheets were previously predicted [1,2], via Random Phase approximation (RPA) arguments, to exhibit an unusual asymptotic van der Waals (vdW) interaction energy $E = - KD^{-3}$ where $D$ is the (large) separation between the two parallel graphene sheets. This is compared with $D^{-5/2}$ for 2D metals [3] and $D^{-4}$ for 2D insulators [3]. Here we show [4] that graphene is the first known system where effects beyond the RPA should make QUALITATIVE changes to the vdW force. For large separations, $D>10 nm$ where only $\pi_z$-mediated vdW forces remain, we predict that the vdW interaction is substantially reduced from the RPA prediction, and has a different power law. This new $D$ dependence is very sensitive to the form of the long-wavelength many-body renormalization of the velocity of the massless Dirac fermions, and may provide independent confirmation of the latter. We will briefly discuss issues involved in possible experiments. \\[4pt] [1] J.F. Dobson, A. White and A. Rubio, Phys. Rev. Lett. 96, 073201 (2006).\\[0pt] [2] T. Gould and J. F. Dobson, Phys. Rev. B 87, 165422 (2013).\\[0pt] [3] M. Bostrom and B. E., Sernelius, Phys. Rev. B 61. 2204 (2000).\\[0pt] [4] J.F. Dobson, T. Gould and G. Vignale, ArXiv 1306.4716 (2013). [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D31.00006: Engineering Graphene Pseudospin Structure with Van der Waals Coupling Chenhao Jin, Zhiwen Shi, Wei Yang, Long Ju, Jason Horng, Guangyu Zhang, Feng Wang Electrons in graphene are described by relativistic Dirac-Weyl spinors with two-component pseudospin. The unique pseudospin structure leads to emerging phenomena such as the massless Dirac cone, anomalous quantum Hall effect, and Klein tunneling. The capability to manipulate electron pseudospin is highly desirable for novel graphene electronics, and is recently achieved by van der Waals coupling to substrate such as graphene/BN and twisted bilayer graphene. We calculate the van der Waals coupled graphene/substrate system and show that the pseudospin structure can be modified in several ways, which will lead to distinctive experimental results. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D31.00007: Scaling Laws for van der Waals Interactions in Nanostructured Materials Vivekanand Gobre, Alexandre Tkatchenko Van der Waals (vdW) forces originate from interactions between fluctuating multipoles in matter and play a significant role in the structure and stability of nanostructured materials. Many models used to describe vdW interactions in nanomaterials are based on a simple pairwise-additive approximation, neglecting the strong electrodynamic response effects caused by long-range fluctuations in matter. We develop and utilize an efficient microscopic method [1,2] to demonstrate that vdW interactions in nanomaterials act at distances greater than typically assumed, and can be characterized by different scaling laws depending on the dimensionality and size of the system. Specifically, we study the behaviour of vdW interactions in single-layer and multilayer graphene, fullerenes of varying size, single-wall carbon nanotubes and graphene nanoribbons. As a function of nanostructure size, the van der Waals coefficients follow unusual trends for all of the considered systems, and deviate significantly from the conventionally employed pairwise-additive picture. We propose that the peculiar van der Waals interactions in nanostructured materials could be exploited to control their self-assembly. [1] Tkatchenko, DiStasio, Car, and Scheffler, PRL (2012); [2] Gobre, Tkatchenko, Nat. Commun. (2013). [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D31.00008: Cohesion Energetics of Carbon Allotropes: Quantum Monte Carlo Study Hyeondeok Shin, Sinabro Kang, Jahyun Koo, Hoonkyung Lee, Jeongnim Kim, Yongkyung Kwon We have performed quantum Monte Carlo calculations to study the cohesion energetics of carbon allotropes, including \textit{sp}$^{\mathrm{3}}$-bonded diamond, \textit{sp}$^{2}$-bonded graphene, \textit{sp}-\textit{sp}$^{\mathrm{2}}$ hybridized graphynes, and \textit{sp}-bonded carbyne. The computed cohesive energies of diamond and graphene are found to be in excellent agreement with the corresponding values determined experimentally for diamond and graphite, respectively, when the zero-point energies, along with the interlayer binding in the case of graphite, are included. We have also found that the cohesive energy of graphyne decreases systematically as the ratio of \textit{sp}-bonded carbon atoms increases. The cohesive energy of $\gamma $-graphyne, the most energetically-stable graphyne, turns out to be 6.766(6) eV/atom, which is smaller than that of graphene by 0.698(12) eV/atom. Experimental difficulty in synthesizing graphynes could be explained by their significantly smaller cohesive energies. Finally we conclude that the cohesive energy of a newly-proposed two-dimensional carbon network can be accurately estimated with the carbon-carbon bond energies determined from the cohesive energies of graphene and three different graphynes. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D31.00009: van der Waals torque Raul Esquivel-Sirvent, George Schatz The theory of generalized van der Waals forces by Lifshtz when applied to optically anisotropic media predicts the existence of a torque. In this work we present a theoretical calculation of the van der Waals torque for two systems. First we consider two isotropic parallel plates where the anisotropy is induced using an external magnetic field. The anisotropy will in turn induce a torque. As a case study we consider III-IV semiconductors such as InSb that can support magneto plasmons. The calculations of the torque are done in the Voigt configuration, that occurs when the magnetic field is parallel to the surface of the slabs. The change in the dielectric function as the magnetic field increases has the effect of decreasing the van der Waals force and increasing the torque. Thus, the external magnetic field is used to tune both the force and torque. The second example we present is the use of the torque in the non retarded regime to align arrays of nano particle slabs. The torque is calculated within Barash and Ginzburg formalism in the nonretarded limit, and is quantified by the introduction of a Hamaker torque constant. Calculations are conducted between anisotropic slabs of materials including BaTiO3 and arrays of Ag nano particles. Depending on the shape and arrangement of the Ag nano particles the effective dielectric function of the array can be tuned as to make it more or less anisotropic. We show how this torque can be used in self assembly of arrays of nano particles. ref. R. Esquivel-Sirvent, G. C. Schatz, Phys. Chem C, 117, 5492 (2013). [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D31.00010: Extended disperson-corrected atom-centered potential (DCACP) approach for treating long-range dispersion interactions in clusters and solids Kenneth Jordan, Ozan Karalti, Wissam Al-Saidi The DCACP method of Rothlisberger and co-workers[1] is one of several strategies for correcting density functional theory for dispersion interactions. The DCACP approach, which involves the use of additional terms in standard pseudopotentials, has proven very successful near the potential energy minima of molecular dimers but gives an interaction energy that falls off much too rapidly as the separation between the monomers is increased. In our work, we extend the DCACP approach for H, C, N, and O to include two angular momenta channels in the pseudopotentials rather than one in the original DCACP method (an idea originally explored by Rothlisberger for (H$_{\mathrm{2}})_{\mathrm{2}})$.[2] We show that this approach, which we designate as DCACP2, significantly improves the description of long-range dispersion interactions. [1] O. A. von Lilienfeld, I. Tavernelli, U. Rothlisberger, and D. Sebastiani, Phys. Rev. Lett., 93, 153004. (2004). [2] I. Tavernelli, I.-C. Lin, and U. Rothlisberger, Phys. Rev. B, 79, 045106, (2009). [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D31.00011: Exchange-correlation functionals for non-covalent interactions Alberto Otero de la Roza, Erin Johnson, Gino DiLabio Dispersion, an essential component of non-covalent interactions, is a long-range correlation effect. The non-covalent binding energies calculated using common density functionals vary widely from overly repulsive to spuriously attractive, and there is no a priori clear recipe for choosing any particular functional. Dispersion in DFT is, as a consequence, as much about calculating the dispersion energy accurately as it is about using a base density functional that gives the correct repulsive wall for all interaction types. In the context of pairwise dispersion corrections, this has been addressed by (over)using the dispersion damping function. In this talk, I present a study on the adequacy of different exchange and correlation approximations for non-covalent interactions as well as an analysis of the energy error scaling with system size. I will show, for instance, that cooperative effects in densely hydrogen-bonded systems (e.g. ice) are consistently overestimated by all density-functional approximations. Our results are relevant regarding the accuracy of molecular dynamics simulations, molecular crystal phase transitions, the scaling of non-covalent interactions to systems of biological interest, and the design of new base functionals for non-covalent interactions. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D31.00012: Long range correlation energy from coupled atomic response functions Alberto Ambrosetti, Alexandre Tkatchenko Electron correlation is an elusive and ubiquitous energy contribution that arises from transient many-body electron excitations. Its reliable (accurate and efficient) modeling is essential for correctly describing cohesive, structural, and response properties of molecules and solids. In this regard, the main challenge is to model the long-range correlation energy beyond (semi-)local density-functional approximations. Here we propose an efficient method to compute the long-range correlation energy for non-metallic molecules and solids, by using coupled atomic response functions (ARF). Extending the recent MBD method [1], we separate the coupling between ARFs into short and long range, allowing seamless treatment of weakly and strongly polarizable systems. Thorough benchmarking on large data sets including small molecules (S22, S66x8), supramolecular complexes (S12L), molecular crystals (X23) and graphite shows consistently good agreement with high level theoretical and experimental reference data (of the order of 6$\%$). The uniform accuracy for molecules and solids represents a strong validation of our method, and further confirms the importance of modeling the truly collective nature of the long-range correlation energy. [1] A. Tkatchenko et al. PRL {\bf 108} 236402 (2012). [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D31.00013: Pair-Wise and Many-Body Dispersive Interactions Coupled to an Optimally Tuned Range-Separated Hybrid Functional Leeor Kronik, Piyush Agrawal, Alexandre Tkatchenko We propose a nonempirical, pair-wise or many-body dispersion-corrected, optimally tuned range-separated hybrid functional. This functional retains the advantages of the optimal-tuning approach in the prediction of the electronic structure. At the same time, it gains accuracy in the prediction of binding energies for dispersively bound systems, as demonstrated on the S22 and S66 benchmark sets of weakly bound dimers. [Preview Abstract] |
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