Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V07: Van der Waals bonding in advanced materials - From van der Waals to CasimirFocus
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Sponsoring Units: DMP Chair: John Dobson, Griffith Univ Room: LACC 153B |
Thursday, March 8, 2018 2:30PM - 3:06PM |
V07.00001: Casimir and van der Waals forces near gently curved surfaces Invited Speaker: Mehran Kardar The proximity force approximation (PFA) relates the interaction between closely spaced, smoothly curved objects to the force between parallel plates. We use a derivative expansion for gently curved surfaces to derive the leading curvature modifications to the PFA for the Casimir force. This approach can also be used to compute the leading and next-to-leading curvature corrections to the Casimir-Polder interaction between a polarizable small particle and a non-planar surface. For anisotropic nanoparticles the force depends on the orientation with respect to the surface; with the preferred orientation a function of curvature, temperature, as well as material properties. We also study the shift of rotational levels of a diatomic polar molecule due to its van der Waals (vdW) interaction with a gently curved dielectric surface at submicron separations. The level shifts, given by the quantum state averaged classical electrostatic interaction of the dipole with its image on the surface, depend on surface curvature and can be estimated by the derivative expansion. We argue that this curvature induced line splitting is experimentally observable. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V07.00002: Unified many-body approach to van der Waals interactions based on semilocal polarizability functional Jan Hermann, Matthias Scheffler, Alexandre Tkatchenko Electromagnetic (EM) coupling of charge fluctuations leads to van der Waals (vdW) and Casimir interactions in systems ranging from small molecules to macroscopic bodies. A promising multiscale approach to unified treatment of vdW and Casimir interactions combines microscopic polarizability models of material response with continuous methods for EM field scattering [1]. But existing polarizability models are either limited in scope (atomic models), in efficiency by working with unoccupied one-particle states (e.g., random-phase approximation), or limited to pairwise approximation (nonlocal density functionals). Here, we present a unified method that combines key elements from different theories, and demonstrate its generality on binding in molecular dimers and crystals, carbon-based nanomaterials, oxides, and salts, as well as on adsorption of molecules on metal surfaces. In particular, we develop a semilocal polarizability functional of the electron density and its gradients to parametrize material response and its coupling within the many-body dispersion framework. Our approach allows consistent modelling of a wide range of materials and hybrid materials with mixed bond types. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V07.00003: Van der Waals Interactions and Radiative Thermal Energy Exchange among Molecules and Macroscopic Bodies Prashanth Venkataram, Jan Hermann, Alexandre Tkatchenko, Alejandro Rodriguez We present a theoretical framework that captures rich quantum and thermal electromagnetic phenomena arising from the coupling of charge (electromagnetic) and vibrational (phononic) fluctuations, including van der Waals interactions and radiative heat transfer among complex molecules and macroscopic objects. Our approach captures atomistic treatments of molecular electronic and vibrational response functions along with continuum models of macroscopic, long-range electromagnetic effects, combining techniques from ab-initio density functional theory (DFT) and classical electromagnetism to describe fluctuation phenomena at wavelengths and separations where the atomism of larger bodies, in contrast to those of molecules, can be neglected, but where the shapes of these objects plays an important role on their electromagnetic response. As a proof of concept, we make predictions of van der Waals interactions and thermal energy transfer among molecules in proximity to metallic and polar-dielectric surfaces that deviate significantly from previous theoretical treatments. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V07.00004: Quantum Friction and Casimir force of Unruh-deWitt detectors and plates. Pablo Rodriguez Lopez, Eduardo Martin-Martinez We revisit the atom-plate quantum friction and Casimir force with a full-relativistic formalism for atoms modelled as Unruh-deWitt detectors in exited, relaxed and coherent superpositions close to a plate. We show that, for relative velocities close to c, the quantum friction diverges while the Casimir force is almost independent of the velocity. We are able to include the effect of the finite size of the detector, then we also obtain quantum friction when the detector is isolated but follows a non-inertial trajectory and we obtain a more realistic result for short distance interactions. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V07.00005: Improving the efficiency of beyond-RPA methods within the dielectric matrix formulation: Algorithms and applications to the A24 and S22 test sets Dario Rocca, Anant Dixit, Julien Claudot, Sebastien Lebegue Within a formalism based on dielectric matrices, the electron-hole time-dependent Hartree-Fock (eh-TDHF) and the adiabatic connection second-order screened exchange (AC-SOSEX) are promising approximations to improve ground-state correlation energies by including exchange effects beyond the random phase approximation (RPA)1. We introduce here an algorithm based on a Gram-Schmidt orthogonalization (GSO) procedure that significantly reduces the number of matrix elements to be computed to evaluate the response functions that enter in the formulation of these two methods2. This approach does not lead to a significant loss of accuracy and extends the applicability of the eh-TDHF and AC-SOSEX to much larger systems. The inclusion of exchange effects beyond the RPA significantly improves the accuracy, with mean absolute errors that decrease by almost 40% for the A24 test set and by almost 50% for the S22 test set. This approach might be used in the future to improve the correlation energy in solid state applications. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V07.00006: A quantum Monte Carlo approach to van der Waals interactions Bartholomew Andrews Although the precise knowledge of van der Waals interactions is crucial for understanding bonding in weakly-bonded layered compounds, there is little quantitative information from either experiments or simulations. We propose to use Diffusion Monte Carlo (DMC) to calculate the strength of interlayer interactions in these materials. The method is widely used to derive the electronic wave function of a molecule or solid subject only to the fixed node approximation, fully accounting for quantum mechanical effects, including van der Waals interactions. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V07.00007: Intermolecular van der Waals Interactions In ''Tight Spaces'' Mainak Sadhukhan, Alexandre Tkatchenko There are strong and substantial experimental indications that intermolecular van der Waals (vdW) interactions become reduced or even repulsive under confinement at surfaces [Phys. Rev. B 81, 035423 (2010)], inside nanotubes [Nature 537, 171 (2016)], and between 2D layers [Phys. Rev. B 94, 220102 (2016)]. These observations remain unexplained by standard treatments of vdW interactions based on a dipolar approximation, which predict universal long-range attraction between vdW dimers. Using the Drude response model of valence electrons, recently we have shown that the long-range electron correlation between spatially confined vdW dimers becomes repulsive when accounting for the full-Coulomb interaction between charge fluctuations [Phys. Rev. Lett. 118, 210402 (2017)]. Here we further develop an atomistic theory for full Coulomb coupled oscillators based on a microscopic many-body dispersion (MBD) Hamiltonian [Phys. Rev. Lett. 108, 236402 (2012)]. We apply this model to study the interplay between London attraction and vdW repulsion for intermolecular interactions in nanotubes, at surfaces, and between 2D materials. We find that repulsive vdW correlations in ``tight spaces'' can provide an additional degree of freedom for molecular self assembly. |
Thursday, March 8, 2018 4:18PM - 4:54PM |
V07.00008: Casimir interactions of complex surfaces and materials Invited Speaker: George Palasantzas Understanding the vacuum state of a system is a challenge of fundamental physics and associated important technologies. If confined within boundaries, quantum vacuum fluctuations manifest themselves by the generation of Casimir forces. However, boundaries between interacting bodies possess in many cases nanoscale surface roughness, which is both difficult to avoid and control. When two bodies are separated by a small distance (less than 100 nm) then nanoscale roughness starts to play an important role on the Casimir interaction between the bodies and their adhesion upon contact. Control of this short-distance interaction is crucial for micro and nanoelectromechanical devices, microfluidics, and bonding technologies. The Casimir forces for flat bodies can be described by the Lifshitz theory that takes into account the actual measured optical properties of the interacting materials. However, for rough surfaces the problem is more complicated by the nonadditivity of the dispersion forces. In this talk I will review the current state of the problem with attention to be given for metallic systems, phase change materials, and poor conductors (promising for operation in severe environments) with respect to adhesion/bonding technologies and actuation dynamics of MEMS/NEMS. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V07.00009: Casimir Polder size consistency: a constraint violated by some dispersion theories Tim Gould, Julien Toulouse, Janos Angyan, John Dobson A key goal in quantum chemistry methods, whether ab initio or otherwise, is to achieve size consistency. In this work we formulate the related idea of "Casimir-Polder size consistency" that manifests in long-range dispersion |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V07.00010: Polarizability and van der Waals radius: Two sides of the same coin Dmitry Fedorov, Mainak Sadhukhan, Martin Stoehr, Alexandre Tkatchenko The atomic polarizability and the van der Waals (vdW) radius are two key quantities to describe |
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