Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules

MBD + C: How to Incorporate Metallic Character into Atom-Based Dispersion Energy Schemes

The dispersion component of the van der Waals interaction in low-dimensional metals is known to exhibit anomalous "Type-C non-additivity" [Int. J. Quantum Chem. 2014, 114, 1157]. This causes dispersion energy behavior at asymptotically large separations that is missed by popular atom-based schemes for dispersion energy calculations. For example, the dispersion interaction energy between parallel metallic nanotubes at separation D falls off asymptotically as approximately D-2, whereas current atom-based schemes predict D-5 asymptotically. To date, it has not been clear whether current atom-based theories also give the dispersion interaction inaccurately at smaller separations for low-dimensional metals. Here, we introduce a new theory that we term "MBD + C". It permits inclusion of Type C effects efficiently within atom-based dispersion energy schemes such as many body dispersion (MBD) and universal MBD (uMBD). This allows us to investigate asymptotic, intermediate, and near-contact regimes with equal accuracy. (The large contact energy of intimate metallic bonding is not primarily governed by dispersion energy and is described well by the semi-local density functional theory.) Here, we apply a simplified version, "nn-MBD + C", of our new theory to calculate the dispersion interaction for three low-dimensional metallic systems: parallel metallic chains of gold atoms, parallel Li-doped graphene sheets, and parallel (4,4) armchair carbon nanotubes. In addition to giving the correct asymptotic behavior, the new theory seamlessly gives the dispersion energy down to near-contact geometry, where it is similar to MBD but can give up to 15% more dispersion energy than current MBD schemes, in the systems studied so far. This percentage increases with separation until nn-MBD + C dominates MBD at asymptotic separations.

Two-Dimensional Six-Body van der Waals Interactions

Van der Waals interactions, primarily attractive van der Waals interactions, have been studied over one and half centuries. However, repulsive van der Waals interactions are less widely studied than attractive van der Waals interactions. In this article, we focus on repulsive van der Waals interactions. Van der Waals interactions are dipole–dipole interactions. In this article, we study the van der Waals interactions between multiple dipoles. Specifically, we focus on two-dimensional six-body van der Waals interactions. This study has many potential applications. For example, the result may be applied to physics, chemistry, chemical engineering, and other fields of sciences and engineering, such as breaking molecules.

Faraday cage screening reveals intrinsic aspects of the van der Waals attraction

General properties of the recently observed screening of the van der Waals (vdW) attraction between a silica substrate and silica tip by insertion of graphene are predicted using basic theory and first-principles calculations. Results are then focused on possible practical applications, as well as an understanding of the nature of vdW attraction, considering recent discoveries showing it competing against covalent and ionic bonding. The traditional view of the vdW attraction as arising from pairwise-additive London dispersion forces is considered using Grimme's "D3" method, comparing results to those from Tkatchenko's more general many-body dispersion (MBD) approach, all interpreted in terms of Dobson's general dispersion framework. Encompassing the experimental results, MBD screening of the vdW force between two silica bilayers is shown to scale up to medium separations as 1.25 de/d, where d is the bilayer separation and de is its equilibrium value, depicting antiscreening approaching and inside de Means of unifying this correlation effect with those included in modern density functionals are urgently required.