37 research outputs found
Adiabatic-connection fluctuation-dissipation density-functional theory based on range separation
An adiabatic-connection fluctuation-dissipation theorem approach based on a
range separation of electron-electron interactions is proposed. It involves a
rigorous combination of short-range density functional and long-range random
phase approximations. This method corrects several shortcomings of the standard
random phase approximation and it is particularly well suited for describing
weakly-bound van der Waals systems, as demonstrated on the challenging cases of
the dimers Be and Ne.Comment: 4 pages, 2 figure
Van der Waals forces in density functional theory: perturbational long-range electron interaction corrections
Long-range exchange and correlation effects, responsible for the failure of
currently used approximate density functionals in describing van der Waals
forces, are taken into account explicitly after a separation of the
electron-electron interaction in the Hamiltonian into short- and long-range
components. We propose a "range-separated hybrid" functional based on a local
density approximation for the short-range exchange-correlation energy, combined
with a long-range exact exchange energy. Long-range correlation effects are
added by a second-order perturbational treatment. The resulting scheme is
general and is particularly well-adapted to describe van der Waals complexes,
like rare gas dimers.Comment: 8 pages, 1 figure, submitted to Phys. Rev.
Interlayer exciton mediated second harmonic generation in bilayer MoS2
Second harmonic generation (SHG) is a non-linear optical process, where two
photons coherently combine into one photon of twice their energy. Efficient SHG
occurs for crystals with broken inversion symmetry, such as transition metal
dichalcogenide monolayers. Here we show tuning of non-linear optical processes
in an inversion symmetric crystal. This tunability is based on the unique
properties of bilayer MoS2, that shows strong optical oscillator strength for
the intra- but also inter-layer exciton resonances. As we tune the SHG signal
onto these resonances by varying the laser energy, the SHG amplitude is
enhanced by several orders of magnitude. In the resonant case the bilayer SHG
signal reaches amplitudes comparable to the off-resonant signal from a
monolayer. In applied electric fields the interlayer exciton energies can be
tuned due to their in-built electric dipole via the Stark effect. As a result
the interlayer exciton degeneracy is lifted and the bilayer SHG response is
further enhanced by an additional two orders of magnitude, well reproduced by
our model calculations.Comment: main paper and supplemen
Patch-like, two dimensional WSe2-based hetero-structures activated by a healing catalyst for H2 photocatalytic generation
2D photoactive materials may offer interesting opportunities in photocatalytic devices since they combine strong light absorption and shortening of charge carriersâ diffusion path. Because of their high surface defect concentration and the formation of a majority of edge/plane vs plane/plane contacts between the anisotropic building blocks, surface defect passivation and improvement of charge carrier transport are critical for the large development of high surface area, 2D photo-catalysts. Here, we propose a hetero-structure nanoporous network with a patch-like coating as high performance 2D photo-catalysts. The hetero-structured building blocks are composed of a photo-active WSe2 nanoflake in direct contact with both a conducting rGO nanosheet and an ultrathin layer of healing catalyst. The resulting nanoporous film achieves a H2 evolution photocurrent density up to 5Â mAÂ cmâ2 demonstrating that the patch-like hetero-structures represent an effective strategy to simultaneously improve hole collection, defect passivation and charge transfer. These hetero-structures made of an ultrathin healing catalyst layer represent promising building blocks for the bottom-up fabrication of high surface area photocathodes particularly for 2D photo-catalysts displaying high defect concentration
Charged iodide in chains behind the highly efficient iodine doping in carbon nanotubes
The origin of highly efficient iodine doping of carbon nanotubes is not well understood. Relying on firstprinciples calculations, we found that iodine molecules (I2) in contact with a carbon nanotube interact to form monoiodide or/and polyiodide from two and three I2 as a result of removing electrons from the carbon nanotube (p-type doping). Charge per iodine atom for monoiodide ion or iodine atom at end of iodine chain is significantly higher than that for I2. This atomic analysis extends previous studies showing that polyiodide ions are the dominant dopants. Moreover, we observed isolated I atoms in atomically resolved transmission electron microscopy, which proves the production of monoiodide. Finally, using Raman spectroscopy, we quantitatively determined the doping level and estimated the number of conducting channels in high electrical conductivity fibers composed of iodine-doped double-wall carbon nanotubes
3D Ruthenium Nanoparticle Covalent Assemblies from Polymantane Ligands for Confined Catalysis
The synthesis of metal nanoparticle (NP) assemblies stabilized by functional molecules is an important research topic in nanoscience, and the ability to control interparticle distances and positions in NP assemblies is one of the major challenges in designing and understanding functional nanostructures. Here, two series of functionalized adamantanes, bis-adamantanes, and diamantanes, bearing carboxylic acid or amine functional groups, were used as building blocks to produce, via a straightforward method, networks of ruthenium NPs. Both the nature of the ligand and the Ru/ligand ratio affect the interparticle distance in the assemblies. The use of 1,3-adamantanedicarboxylic acid allows the synthesis of three-dimensional (3D) networks of 1.7â1.9 nm Ru NPs presenting an interparticle distance of 2.5â2.7 nm. The surface interaction between Ru NPs and the ligands was investigated spectroscopically using a 13C-labeled ligand, as well as theoretically with density functional theory (DFT) calculations. We found that Ru species formed during the NP assembly are able to partially decarbonylate carboxylic acid ligands at room temperature. Decarbonylation of a carboxylic acid at room temperature in the presence of dihydrogen usually occurs on catalysts at much higher temperatures and pressures. This result reveals a very high reactivity of ruthenium species formed during the network assembly. The Ru NP networks were found to be active catalysts for the selective hydrogenation of phenylacetylene, reaching good selectivity toward styrene. Overall, we demonstrated that catalyst activity, selectivity, and NP network stability are significantly affected by Ru NP interparticle distance and electronic ligand effects. As such, these materials constitute a unique set that should allow a better understanding of the complex surface chemistry in carbon-supported metal catalysts
Mo thio and oxo-thio molecular complexes film as self-healing catalyst for photocatalytic hydrogen evolution on 2D materials
2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cmâ2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties
python in the Physical Chemistry lab [pyPhysChem]
pyPhysChem proposes a series of Jupyter notebooks intended to introduce physical chemistry students to the Python computer language. These Jupyter notebooks were designed to cover a wide variety of topics, including data analysis and machine learning.If you use this software, please cite it using the metadata from this fil