Dispersion interaction in hydrogen-chain models

Abstract

We have investigated the dispersion interaction in hydrogen chain models via density functional theory-based symmetry-adapted perturbation theory using the asymptotically corrected PBE0 energy functional. The quasimetallic and the insulating prototype systems were chosen to be hydrogen chains with equally and alternately spaced H(2) units, respectively. The dependence of the dispersion energy on the chain length for quasimetallic and insulating cases has been determined for two chains arranged either in pointing or in parallel geometries. The results are compared with those previously calculated from a continuum coupled-plasmon approach [Phys. Rev. B 77, 075436 (2008)]. The interaction energy has also been modeled by pairwise summations over short fragments of the chains, demonstrating the failure of the additivity principle for the quasimetallic case, while confirming that the additivity is a qualitatively reasonable hypothesis for the insulating case.

Layer response theory: Energetics of layered materials from semianalytic high-level theory

“…The leading term in the infinite stack result (51) is twice the two-layer result (40), which makes sense because in the infinite stack each layer has two nearest-neighbour layers.…”

“…Putting this into (39), for example, we obtain a sub-asymptotic correction to (40) for the cross-correlation energy of two identical insulating layers…”

“…At moderate inter-layer distances D the inverse exponential e −2QD , from the Coulomb potential in correlation energy expressions such as (40), creates a natural cutoff ensuring that the unphysical large-Q behaviour of our small-Q resonse expressions (69,70) does not contribute significantly to the energy. However, as the two layers approach their natural binding distance D 0 this exponential decay is insufficient for the task, and we need to recognize that the Q integrations should at least be restricted to the first Brillouin zone.…”

“…In particular, the RPA approach correctly describes the very long-wavelength charge fluctuations not captured in pairwise theories, but responsible for anomalous long-ranged van der Waals interactions 25 . These differences from the pairwise predictions are manifested in both the dependence of the energy on layer spacing D 25,40 and, for finite systems, on the number of atoms N 27,29 . Furthermore, the RPA (without extensions) has been shown 33 to give simultaneously a good description of the layer spacing, the breathing elastic constant C 33 and the layer binding energy of graphite, a task that proved elusive with other methods.…”

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

“…For the one-dimensional case of two parallel metallic nanotubes at separation Z, the conventional summed result is E (Z) ∝ −Z −5 whereas more acurate microscopic approaches yield E (Z) ∝ −Z −2 (ln |z|) −3/2 [6], [4], [7] [8] in the electromagnetlicaly non-retarded regime. These 2D and 1D nanosystems were argued [4], [9], [10], [11] to exhibit unconvential vdW powers because of their zero electronic energy gap and their low dimensionality (limiting the influence of coulomb screening). In a recent work [9], these unconventional dispersion power laws were attributed to "Type-C vdW non-additivity" arising from the de-localization (hopping) of electrons between nuclear centres, i.e.…”