Van der Waals interactions between graphitic nanowiggles

Abstract

The van der Waals interactions between two parallel graphitic nanowiggles (GNWs) are calculated using the coupled dipole method (CDM). The CDM is an efficient and accurate approach to determine such interactions explicitly by taking into account the discrete atomic structure and many-body effect. Our findings show that the van der Waals forces vary from attraction to repulsion as nanoribbons move along their lengths with respect to each other. This feature leads to a number of stable and unstable positions of the system during the movement process. These positions can be tuned by changing the length of GNW. Moreover, the influence of the thermal effect on the van der Waals interactions is also extensively investigated. This work would give good direction for both future theoretical and experimental studies.

Unifying Microscopic and Continuum Treatments of van der Waals and Casimir Interactions

“…Energy ratio E=E PWS versus z for a fullerene (solid blue), protein (solid green), or wire in the parallel (solid red) or perpendicular (solid black) orientations, above the gold plate; E PWS is the energy obtained by a pairwise approximation defined in (10). Also shown are the predictions of both CP (dotted red) and nonretarded (dashed red) approximations for the case of a parallel wire.…”

“…It has long been known that vdW interactions among a system of polarizable atoms are not pairwise additive but instead strongly depend on geometric and material properties [2,4,5]. However, only recently developed theoretical methods have made it possible to account for short-range quantum interactions in addition to long-range many-body screening in molecular ensembles [3,[6][7][8][9][10][11][12][13][14][15], demonstrating that nonlocal many-body effects cannot be captured by simple, pairwise-additive descriptions; these calculations typically neglect electromagnetic retardation effects in molecular systems. Simultaneously, recent theoretical and experimental work has characterized dipolar Casimir-Polder (CP) interactions between macroscopic metallic or dielectric objects and atoms, molecules, or Bose-Einstein condensates, further extending to nonzero temperatures, dynamical situations, and fluctuations in excited states (as in so-called Rydberg atoms) [16][17][18][19][20][21][22][23][24][25].…”

“…The particular molecules we consider have finite electronic gaps, allowing accurate description of the bare response via sums over dipolar ground-state oscillator densities [5,[8][9][10]12,14,43],…”

Impact of nuclear vibrations on van der Waals and Casimir interactions at zero and finite temperature

“…both the forces themselves and their differences with respect to temperature should therefore be measurable and resolvable in state-of-the-art Casimir experiments [50], though it should be pointed out that that long free-standing carbyne wires have not been stably fabricable, and carbyne has only been found in solution or confined to supramolecular structures like carbon nanotubes [51,52].…”

“…Within the Unsöld approximation, for the purpose of constructing the molecular response, the electronic oscillator in each atom is initially taken to be undamped (with dissipation to be added later); given α ep (0), the electronic oscillator frequencies ω ep are computed by fitting the oscillator dispersion to nonretarded vdW C 6 -coefficients for each atom taken from a large reference of theoretical and experimental atomic and small molecular data [4,6,39]. From this, the effective number of electrons n ep associated with that atom can be determined, and so can the effective charge q ep = n ep q e , mass m ep = n ep m e , and isotropic spring constant k ep ; these quantities, by virtue of deriving from α ep (0) and ω ep , encode the same short-range quantum and electrostatic effects present in DFT and other high-level quantum calculations [6,7,[34][35][36][37][38]. The nuclear masses are taken from elemental data as they are four orders of magnitude larger than the electronic masses, while the internuclear spring constants K pq are computed as the second spatial derivatives of the ground-state energy in DFT with respect to the nuclear coordinates at equilibrium.…”