Including Van Der Waals Corrections Research Articles

Strain-induced surface modalities in pnictogen chalcogenide topological insulators

We study the role of equi-biaxial strains on the electronic structure in pnictogen chalcogenides Bi2Se3, Bi2Te3, and As2Te3. Bi2Se3 and Bi2Te3 are topological insulators, and As2Te3 is an insulator with a relatively small bandgap. Based on the results of density functional theory calculations including van der Waals corrections, we demonstrate that a topological insulator (TI) state in As2Te3 can be induced by an epitaxial (in-plane) tensile misfit strain of 1%. Furthermore, we find overall that the effect of the misfit on the bandgap is larger for As2Te3 than for Bi2Se3 and Bi2Te3. We attribute this to a complex interplay between the misfit strain, spin–orbit coupling, and the relaxation of surface atomic layers. Our findings indicate that As2Te3 is more suitable than Bi2Se3 and Bi2Te3 for potential applications of strain-induced switching of TIs.

Density-functional study of hydrazine doped single-walled carbon nanotubes as an n-type semiconductor

The theoretical study of hydrazine in the presence of moisture doped single-walled carbon nanotube (SWCNT) where the donor state (DS) occurred in the electronic band structure, which has previously been reported. Herein, We reveal that the density functional theory (DFT) studies of pure hydrazine formed the hydrogen bond network (HBN) on SWCNT, leading to the n-type behavior. DFT approaches including van der Waals corrections were carried out to understand the specific configuration of hydrazine, which causes the occurrence of the DS. The electronic band structures are classified according to three groups. First, is the impurity state below the maximum valence state (ISBMVS). Second, is the impurity state close to (below) the maximum valence state (ISCMVS), and third, is the DS. The reduced density gradient (RDG) approach and the Bader charge analysis were used to address a specific hydrazine molecule, which caused the DS to occur. The NMR chemical shifts and UV–Vis spectroscopic parameters can be used for comparison with experiments to confirm the theoretical models. • The electronic calculation reveals hydrazine doped SWCNTs are n-type semiconductors. • Effect of structure optimization was found crucial to discover a specific hydrogen bonded on hydrazine network. • 13 C NMR and 1 H NMR data were analyzed via periodic DFT calculations. • The proposed of photon absorption energy and optical transition in IS and DS with TDDFT framework are agreement with experimental data.

Atomic structures and orbital energies of 61,489 crystal-forming organic molecules

Data science and machine learning in materials science require large datasets of technologically relevant molecules or materials. Currently, publicly available molecular datasets with realistic molecular geometries and spectral properties are rare. We here supply a diverse benchmark spectroscopy dataset of 61,489 molecules extracted from organic crystals in the Cambridge Structural Database (CSD), denoted OE62. Molecular equilibrium geometries are reported at the Perdew-Burke-Ernzerhof (PBE) level of density functional theory (DFT) including van der Waals corrections for all 62 k molecules. For these geometries, OE62 supplies total energies and orbital eigenvalues at the PBE and the PBE hybrid (PBE0) functional level of DFT for all 62 k molecules in vacuum as well as at the PBE0 level for a subset of 30,876 molecules in (implicit) water. For 5,239 molecules in vacuum, the dataset provides quasiparticle energies computed with many-body perturbation theory in the G0W0 approximation with a PBE0 starting point (denoted GW5000 in analogy to the GW100 benchmark set (M. van Setten et al. J. Chem. Theory Comput. 12, 5076 (2016))).

Temperature-Dependent Stability of Polytypes and Stacking Faults inSiC: Reconciling Theory and Experiments

The relative stability of SiC polytypes, changing with temperature, has been considered a paradox for about thirty years, due to discrepancies between theory and experiments. Based on ab-initio calculations including van der Waals corrections, a temperature-dependent polytypic diagram consistent with the experimental observations is obtained. Results are easily interpreted based on the influence of the hexagonality on both cohesive energy and entropy. Temperature-dependent stability of stacking faults is also analyzed and found to be in agreement with experimental evidences. Our results suggest that lower temperatures during SiC crystal deposition are advantageous in order to reduce ubiquitous stacking faults in SiC-based power devices.

Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μB distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of -1.45 and 1.45 eV.

Steering On-Surface Self-Assembly of High-Quality Hydrocarbon Networks with Terminal Alkynes

The two-dimensional (2D) self-assembly of 1,3,5-triethynyl-benzene (TEB) and de novo synthesized 1,3,5-tris-(4-ethynylphenyl)benzene (Ext-TEB) on Ag(111) was investigated by means of scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Both 3-fold symmetric molecules form long-range ordered nanoporous networks featuring organizational chirality, mediated by novel, planar 6-fold cyclic binding motifs. The key interaction for the expression of the motifs is identified as C–H···π bonding. For Ext-TEB, an additional open-porous phase exists with the 3-fold motif. The nature of the underlying noncovalent bonding schemes is thoroughly analyzed by density functional theory (DFT) calculations including van der Waals corrections. The comparison of calculations focusing on isolated 2D molecular sheets and those including the substrate reveals the delicate balance between the attractive molecule–molecule interaction, mediated by both the terminal alkyne and the phenyl groups, and the molecule–substrate interaction responsible for the commensurability and the regularity of the networks. Comparison with bulk structures of similar molecules suggests that these strictly planar cyclic binding motifs appear only in 2D environments.

Accounting for van der Waals interactions between adsorbates and surfaces in density functional theory based calculations: selected examples

This article reviews the different density functional theory (DFT) methods available in the literature for dealing with dispersion interactions and recent applications of DFT approaches including van der Waals corrections in the study of the interaction of atoms and molecules with several different surfaces. Focus is given to the interaction of atoms and molecules with metal, metal oxide and graphite surfaces or more complex systems. It will be shown that DFT approaches including van der Waals corrections present significant advances over standard exchange–correlation functionals for treating systems dominated by weak interactions.

Integrated X-ray photoelectron spectroscopy and DFT characterization of benzene adsorption on Pt(111), Pt(355) and Pt(322) surfaces

We systematically investigate the adsorption of benzene on Pt(111), Pt(355) and Pt(322) surfaces by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principle calculations based on density functional theory (DFT), including van der Waals corrections. By comparing the adsorption energies at 1/9, 1/16 and 1/25 ML on Pt(111), we find significant lateral interactions exist between the benzene molecules at 1/9 ML. The adsorption behavior on Pt(355) and Pt(322) is very different. While on Pt(355) a step species is clearly identified in the C 1s spectra at low coverages followed by occupation of a terrace species at high coverages, no evidence for a step species is found on Pt(322). These different adsorption sites are confirmed by extensive DFT calculations, where the most favorable adsorption configurations on Pt(355) and Pt(322) are also found to vary: a highly distorted across the step molecule is found on Pt(355) while a less distorted configuration adjacent to the step molecule is deduced for Pt(322). The theoretically proposed C 1s core level binding energy shifts between these most favorable configurations and the terrace species are found to correlate well with experiment: for Pt(355), two adsorbate states are found, separated by ~0.4 eV in XPS and 0.3 eV in the calculations, in contrast to only one state on Pt(322).