Tractable non-local correlation density functionals for flat surfaces and slabs

A systematic approach for the construction of a density functional for van der Waals interactions that also accounts for saturation effects is described, i.e. one that is applicable at short distances. A very efficient method to calculate the resulting expressions in the case of flat surfaces, a method leading to an order reduction in computational complexity, is presented. Results for the interaction of two parallel jellium slabs are shown to agree with those of a recent RPA calculation (J.F. Dobson and J. Wang, Phys. Rev. Lett. 82, 2123 1999). The method is easy to use; its input consists of the electron density of the system, and we show that it can be successfully approximated by the electron densities of the interacting fragments. Results for the surface correlation energy of jellium compare very well with those of other studies. The correlation-interaction energy between two parallel jellia is calculated for all separations d, and substantial saturation effects are predicted.Comment: 10 pages, 6 figure

Typifications and nomenclatural notes in Physalis (Solanaceae) from the United States

Physalis is an economically important and morphologically diverse genus of plants with solitary flowers and fruits that are enveloped by an inflated fruiting calyx. Although work to resolve phylogenetic relationships in this clade is ongoing, Physalis remains a taxonomically complex genus with multiple nomenclatural problems. Here, we review 28 species from the United States and their synonyms as well as clarification on the status of their types. We propose 53 typifications. We select a lectotype for 49 names and a neotype for three names (P. ixocarpa, P. linkiana, P. ramosissima). We additionally designate an epitype for P. longifolia.Fil: Pretz, Chelsea. University of Colorado; Estados UnidosFil: Deanna, Rocío. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Farmacia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. University of Colorado; Estados Unido

Tetrahedral bonding in twisted bilayer graphene by carbon intercalation

Based on ab initio calculations, we study the effect of intercalating twisted bilayer graphene with carbon. Surprisingly, we find that the intercalant pulls the atoms in the two layers closer together locally when placed in certain regions in between the layers, and the process is energetically favorable as well. This arises because in these regions of the supercell, the local environment allows the intercalant to form tetrahedral bonding with nearest atoms in the layers. Intercalating AB- or AA-bilayer graphene with carbon does not produce this effect; therefore, the nontrivial effect owes its origin to both using carbon as an intercalant and using twisted bilayer graphene as the host. This opens new routes to manipulating bilayer and multilayer van der Waals heterostructures and tuning their properties in an unconventional way