Using first-principles calculations, we investigate the interactions between a WS2 monolayer and several gas molecules (CO, H2O, NO, and O2). Different sets of calculations are performed based on generalized-gradient approximations (GGAs) and GGA + U ([Formula: see text] eV) calculations with D2 dispersion corrections. In general, GGA and GGA + U establish good consistency with each other in terms of absorption stability and band gap estimations. Van der Waals density functional (vdW-DF) calculations are also performed to validate long-range gas molecule-WS2 monolayer interactions, and the resultant absorption energies of four gas-absorption cases (from 0.21 to 0.25 eV) are significantly larger than those obtained from calculations using empirical D2 corrections (from 0.11 to 0.19 eV). The reported absorption energies clearly indicate van der Waals interactions between the WS2 monolayer and gas molecules. The NO and O2 absorptions are shown to narrow the band gaps of the WS2 material to 0.75-0.95 eV and produce small magnetic moments (0.71 μB and 1.62 μB, respectively). Moreover, these two gas molecules also possess good charge transferability to WS2. This observation is important for NO- and O2-sensing applications on the WS2 surface. Interestingly, WS2 can also activate the dissociation of O2 with an estimated barrier of 2.23 eV.

We investigate the Kb characteristic radiation and the complex asymmetric structure of photoemission lines of copper, which provides a benchmark for theoretical and experimental studies of x-ray calibration series in transition metals. Ab initio multi-configuration Dirac-Hartree-Fock (MCDHF) calculations have been performed to study the complex open-shell many-electron problem in copper. The biorthogonalization technique permits determination of transition intensities and Einstein A coefficients. The results from our MCDHF calculations demonstrate excellent convergence in transition energies and intensities, as well as gauge invariance to 0.6%. Shake processes caused by single and double spectator vacancies from 3d, 3p, 3s and 4s subshells have also been investigated extensively. MCDHF has been performed to calculate energies and relative intensities of 3d, 3d 2 , 3p, 3s and 4s satellites, resulting in the total number of configuration states exceeding 100 000 and more than 1500 transition components. Our theoretical calculations of shake-off probabilities using the multi-configuration method in the sudden limit have a high degree of internal consistency with the best available experimental data for copper Kb. This supports the validity of relativistic atomic theory and sets a new benchmark even for poorly resolved characteristic spectra using current techniques of analysis.

The adsorption of metals on the silicene monolayer may potentially offer advantageous applications in electronic and spintronic devices. In this study, by employing first-principles calculations, we investigate the attachment of two 3d transition metals (Fe and Cr) on buckled and planar silicene surfaces. Besides examining structural stability, we also explore interesting ferromagnetic as well as half-metallic features of the material. All Fe adsorption cases are found to be more stable (with the lowest binding energy being 3.39 eV) than Cr adsorption cases. When the metal adsorption rate is high, Fe tends to penetrate into both buckled and planar silicene layers. This insertion behavior allows the 3d shells of Fe to enhance bonding interactions with all 3p x , 3p y , and 3p z orbitals of Si, thus producing more stable structures. The adsorptions of Cr with high distribution ratio are found to be more stable than the low-Cr-distribution structures. It is observed that Cr does not penetrate into the silicene layer like Fe. Overall, ferromagnetism is dominant with five nanostructures. Two Cr adsorption cases on planar silicene preferentially behave as antiferromagnets, and one Fe adsorption case is nonmagnetic. From our observation, there is an inversed interplay between structural stability and magnetic moments; i.e., FeSi x nanostructures (more stable) tend to exhibit lower ferromagnetic moments. The half-metallic characteristic is found in four nanostructures, which can be potentially applied in spin-electronic devices. The gaps derived from spin-down states for those half-metallic nanostructures vary from 0.28 to 0.57 eV.

We study the energy-loss function for lead in the framework of the time-dependent density functional theory, using the full-potential linearized augmented plane-wave plus local orbitals method. The ab initio calculations are performed in the adiabatic local density approximation. The comparison between the obtained energy-loss function for zero momentum transfer with those from reflection electron energy loss spectroscopy measurements and from first-principles calculations shows good agreement.

No abstract