Thomas Heine

The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect ban

The components of nucleus-independent chemical shift (NICS) tensors for Dnhn-annulenes are discussed as indexes of the aromatic character of electronic π systems. The component corresponding to the principal axis perpendicular to the ring plane, NICSzz, is found to be a good measure for the characterisation of the π system of the ring. Isotropic NICS values at ring centres contain large influences from the σ system and from all three principal components of the NICS tensor. At large distances aw

We propose a two-dimensional crystal that possesses low indirect band gaps of 0.55 eV (monolayer) and 0.43 eV (bilayer) and high carrier mobilities similar to those of phosphorene, GeP 3 . GeP 3 has a stable three-dimensional layered bulk counterpart, which is metallic and known from experiment since 1970. GeP 3 monolayer has a calculated cleavage energy of 1.14 J m –2, which suggests exfoliation of bulk material as viable means for the preparation of mono- and few-layer materials. The material

CONSPECTUS: After the discovery of graphene and the development of powerful exfoliation techniques, experimental preparation of two-dimensional (2D) crystals can be expected for any layered material that is known to chemistry. Besides graphene and hexagonal boron nitride (h-BN), transition metal chalcogenides (TMC) are among the most studied ultrathin materials. In particular, single-layer MoS2, a direct band gap semiconductor with ∼1.9 eV energy gap, is popular in physics and nanoelectronics, b

The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C(6)H(6), D(6h)), anti-aromatic (C(4)H(4), D(2h)) and non-aromatic (C(4)H(8), D(4h), and C(6)H(12), D(3d)) molecules. The results show that molecules that contain a pi system possess a long-range magnetic response, while the induced magnetic field is sho

The Universal Force Field (UFF) (Rappé et al., J. Am. Chem. Soc. 1992) provides a general approach to molecular mechanics for molecules and materials composed of elements throughout the periodic table. Though the method is tunable by the specification of bond orders and the introduction of effective charges, the presently available list of atom types is insufficient to treat various systems containing transition metals, including metal-organic frameworks (MOFs). As MOFs are composite materials b

Aromaticity is indispensable for explaining a variety of chemical behaviors, including reactivity, structural features, relative energetic stabilities, and spectroscopic properties. When interpreted as the spatial delocalization of π-electrons, it represents the driving force for the stabilization of many planar molecular structures. A delocalized electron system is sensitive to an external magnetic field; it responds with an induced magnetic field having a particularly long range. The shape of

Transition-metal dichalcogenides TX2 (T = W, Mo; X = S, Se, Te) are layered materials that are available in ultrathin forms such as mono-, bi- and multilayers, which are commonly known as two-dimensional materials. They have an intrinsic band gap in the range of some 500 meV to 2 eV, depending on the composition and number of layers, and giant intrinsic spin-orbit splittings for odd layer numbers, and, in conjunction with their high chemical and mechanical stability, they qualify as candidate ma

The structure and electronic structure of layered noble-transition-metal dichalcogenides MX2 (M=Pt and Pd, and chalcogenides X=S, Se, and Te) have been investigated by periodic density functional theory (DFT) calculations. The MS2 monolayers are indirect band-gap semiconductors whereas the MSe2 and MTe2 analogues show significantly smaller band gap and can even become semimetallic or metallic materials. Under mechanical strain these MX2 materials become quasi-direct band-gap semiconductors. The

Covalent-Organic Frameworks (COFs) are a new family of 2D and 3D highly porous and crystalline materials built of light elements, such as boron, oxygen and carbon. For all 2D COFs, an AA stacking arrangement has been reported on the basis of experimental powder XRD patterns, with the exception of COF-1 (AB stacking). In this work, we show that the stacking of 2D COFs is different as originally suggested: COF-1, COF-5, COF-6 and COF-8 are considerably more stable if their stacking arrangement is

We boost the ORR performance of Fe–N–C electrocatalysts in acids by engineering highly accessible and dense surface single metal FeN 4 active sites.

A review. The following topics are discussed: interaction of mols. with magnetic field (shielding function); special NMR properties of arom. mols.; magnetically induced current densities and related models; induced magnetic fields of mols.; electron delocalization and magnetic response for some mols. [on SciFinder (R)]

The aluminosilicate mineral imogolite is composed of single-walled nanotubes with stoichiometry of (HO)(3)Al(2)O(3)SiOH and occurs naturally in soils of volcanic origin. In the present work we study the stability and the electronic and mechanical properties of zigzag and armchair imogolite nanotubes using the density-functional tight-binding method. The (12,0) imogolite tube has the highest stability of all tubes studied here. Uniquely for nanotubes, imogolite has a minimum in the strain energy

Spin‐orbit splitting in transition‐metal dichalcogenide monolayers is investigated on the basis of density‐functional theory within explicit two‐dimensional periodic boundary conditions. The spin‐orbit splitting reaches few hundred meV and increases with the size of the metal and chalcogen atoms, resulting in nearly 500 meV for WTe 2 . Furthermore, we find that similar to the band gap, spin‐orbit splitting changes drastically under tensile strain. In centrosymmetric transition metal dichalcogeni

One of the major obstacles to a wide application range of the quantum spin Hall (QSH) effect is the lack of suitable QSH insulators with a large bulk gap. By means of first-principles calculations including relativistic effects, we predict that methyl-functionalized bismuth, antimony, and lead bilayers (Me-Bi, Me-Sb, and Me-Pb) are 2D topological insulators (TIs) with protected Dirac type topological helical edge states, and thus suitable QSH systems. In addition to the explicitly obtained topol