We report computer assisted density functional theory computations of electronic states in carbide Co9S8/MoS2 interface model. The interface model was previously proposed using crystallographic information from experimental high-resolution TEM observations; and directly observed by in-situ heating to confirm carbon deposit occurs at the sulfur edge of Co9S8/MoS2 which creates a thin carbide layer. In here, the total energy for carbon adsorption results eight times more favorable to occur at sulfur edge in comparison to molybdenum or cobalt replacement by permutation of carbon atoms as contained in C, CH, CH2 species by exothermic energies. Amorphous carbon excites 2 pz orbitals as observed on density of states near Fermi level (F E ), and 13% decreased in terms of charge carriers available, causing to decrease its chemical catalytic reactivity and bending of MoS2 slabs as carbon starts to accumulate at the sulfur edge mainly, which is attributed to charge distribution around the adsorption site caused by the foreign atoms, confirmed by electron density plots, that acts as ‘electron traps’. This helps us concluding that carbon replacement can induce change of selectivity in direct desulfurization pathway.

In this work, we investigated the electronic structure and the quantum capacitance of a set of functionalized MoS2 monolayers. The functionalizations have been done by using different ad-atom adsorption on MoS 2 monolayer. Density functional theory calculations are performed to obtain an accurate electronic structure of ad-atom doped MoS2 monolayer with a varying degree of doping concentration. Subsequently, the quantum capacitance in each functionalized system was estimated. A marked quantum capacitance above 200 μF cm−2 has been observed. Our calculations show that the quantum capacitance of MoS2 monolayer is significantly enhanced with substitutional doping of Mo with transition metal ad-atoms. The microscopic origin of such enhancement in quantum capacitance in this system has been analyzed. Our DFT-based calculation reveals that the generation of new electronic states at the proximity of the band-edge and the shift of Fermi level caused by the ad-atom adsorption results in a very high quantum capacitance in the system.

Since the rising of graphene, boron nitride monolayers have been deeply studied due to their structural similarity with the former. A hexagonal graphene-like boron–carbon–nitrogen (h-BCN) monolayer was synthesized recently using bis-BN cyclohexane (B2N2C2H12) as a precursor molecule. Herein, we investigated the electronic and structural properties of this novel BCN material, in the presence of single-atom (boron, carbon, or nitrogen) vacancies, by employing density functional theory calculations. The stability of these vacancy-endowed structures is verified from cohesion energy calculations. Results showed that a carbon atom vacancy strongly distorts the lattice leading to breaking on its planarity and bond reconstructions. The single-atom vacancies induce the appearance of flat midgap states. A significant degree of charge localization takes place in the vicinity of these defects. It was observed a spontaneous magnetization only for the boron-vacancy case, with a magnetic dipole moment about 0.87 μ B .Our calculations predicted a direct electronic bandgap value of about 1.14 eV. Importantly, this bandgap value is intermediate between gapless graphene and insulating hexagonal boron nitride.

Plane wave density functional theory codes generally assume periodicity in all three dimensions. This causes difficulties when studying charged systems, for instance energies per unit cell become infinite, and, even after being renormalised by the introduction of a uniform neutralising background, are very slow to converge with cell size. The periodicity introduces spurious electric fields which decay slowly with cell size and which also slow the convergence of other properties relating to the ground state charge density. This paper presents a simple self-consistent technique for producing rapid convergence of both energies and charge distribution in the particular geometry of 2D periodicity, as used for studying surfaces.

Transition metal nitrides possess important properties of interest such as superconductivity, high hardness, optical, electronic and magnetic among others which are relevant for technological applications. In this study, structural and magnetic properties of nitrides of iron and nickel have been investigated using generalized gradient approximation of Perdew–Burke–Ernzerhof revised for solids (GGA-PBEsol) as implemented in Quantum Espresso, a density functional theory based computational software package. The compounds were considered in the zinc blende face centered cubic (FCC), hexagonal closed packed (HCP) and primitive tetragonal structures and the results revealed that FeN and NiN energetically prefer zinc blende FCC structure. The results of spin polarized calculation indicated that FeN exhibited non-magnetic properties only in the zinc blende FCC structure and a magnetic moment of 2.17 μ B and 3.18 μ B per formula units in the HCP and primitive tetragonal structures respectively, whereas NiN was non-magnetic for the three crystal structures.

A carbon quantum dot (CQD) sample series was synthesized from citric acid and varying concentrations of thiourea. The highest (sample 1) and lowest (sample 2) concentrations of thiourea exhibited unique visual effects and electronic structures. X-ray excited optical luminescence (XEOL) along with UV-visible spectroscopy provided unique insight into the absorption and emission mechanisms of samples 1 and 2, where only sample 2 emitted XEOL. Sample 1 exhibited the commonly observed aggregation caused quenching (ACQ) effects in the solid state. While sample 2 displayed unique aggregation induced emissions (AIE) effects upon exciting the sample above the C K edge. The AIE and ACQ sample differences were suspected to be from S moiety differences arising from the varying thiourea concentrations during synthesis. Furthermore, x-ray absorption spectroscopy (XAS) in modes of total electron yields (TEY) and partial fluorescence yields (PFY) allowed the identification of specific core and surface states of the CQDs. It was discovered that thiophene moieties were uniquely formed in the AIE sample’s surface and not anywhere in the ACQ CQD sample. The thiophene surface functionality is believed to be a significant contributor to the AIE effects seen in the XEOL studies. Understanding and preventing the common CQD ACQ mechanism allows the application of CQDs in solid lighting applications.

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