Atomistic observation of the collision and migration of Li on MoSe2 and WS2 surfaces through ab initio molecular dynamics

We present in this study a theoretical investigation of the collision of Li with the MX₂ surface (MoSe₂ or WS₂) by employing the Born-Oppenheimer molecular dynamics (MD) approach. In each trajectory, atomic Li is fired toward the two-dimensional monolayer with an inletting kinetic energy of 0.2 eV or 2.0 eV and a chosen striking angle. In total, 84 MD trajectories are analyzed. We observe that Li has a high tendency to migrate on WS₂ in most investigated cases (20/21 cases at 0.2 eV inletting kinetic energy and 21/21 cases at 2.0 eV inletting kinetic energy), while the migration probability on MoSe₂ is much lower (only 5/21 cases with the inletting kinetic energy of 0.2 eV and 15/21 cases with the inletting kinetic energy of 2.0 eV). Interestingly, our finding shows that the migration probability does not depend on the binding energies of Li-MoSe₂ (1.61 eV) and Li-WS₂ (1.77 eV), but it is in good agreement with the nudged-elastic-band prediction of migration barriers. In fact, it is the intensity of elastic vibration of the transition metal dichalcogenide layer that plays a very significant role in the migration of Li. During the collision process, Li is able to absorb energy from the layer vibration to jump out from one X-X-X trap to another. Consequently, with the assistance from intensive vibration of WS₂, Li would possess higher migration probability on the layer surface. Finally, electronic structure analysis on various interacting Li-MX₂ configurations is performed. From Bader charge estimation, we observe that WS₂ tends to establish more charge transferability with Li. Moreover, when Li approaches closer to the S/Se layer, the hybridization of Li-2s and Mo-4d (or W-5d) orbitals results in a magnetic moment (up to ∼1 μ_B).

Adjusting band gap and charge transfer of organometallic complex adsorbed on MoS2 monolayer using vertical electric-field: a first-principles investigation

In this paper, we propose the use of benzene (Bz) to cover the active site on top of a transition metal atom (Cr/Mn/Fe) adsorbed on the MoS₂ monolayer. Stable configurations of adatom on the MoS₂ surface were predicted using first-principles calculations and their electronic, magnetic properties were investigated. In addition, the influence of vertical electric field on the electronic band structures of the systems was carefully examined. Analyzing the adsorption energies of transition metals given by the PBE calculations, we found that the benzene molecule stabilized the binding of Cr and Mn on the MoS₂ surface, but destabilized the Fe binding by approximately 33% of adsorption energy. The attachment of benzene caused modifications on the total magnetizations of the Cr-MoS₂ and Mn-MoS₂ structures. The Bz-Mn@MoS₂ structure was found to exhibit half-metallicity with 100% spin polarization at the Fermi level. The influence of various degrees of vertical electric field was shown to produce a tensile stress, which altered the lattice parameters and led to band gap narrowing and dramatic shifts of the Fermi level.

First-principles modeling of 3d-transition-metal-atom adsorption on silicene: a linear-response DFT + U approach

By employing DFT  +  U calculations with the linear response method, we investigate the interactions between various 3d transition-metal atoms (Cr, Mn, Fe, Co) and silicene. In the cases of two-dimensional (2D) FeSi2 and CoSi2, the metal atoms tend to penetrate into the silicene layer. While CoSi2 is non-magnetic, FeSi2 exhibits a total magnetic moment of 2.21 μ(B)/cell. Upon the examination of 2D MSi6, a trend in anti-ferromagnetic (AFM) favorability in the z-direction is observed according to our DFT  +  U calculations. In the ferromagnetic (FM) states (less stable), each primary unit cell of CrSi6, MnSi6, and FeSi6 possesses different levels of total magnetization (4.01, 5.18, and 2.00 μ B/cell, respectively). The absolute magnetization given by AFM MSi6 structures varies in the range of 5.33-5.84 μ(B)/cell. A direct band gap in AFM MnSi6 (0.2 eV) is predicted, while the metastable FM FeSi6 structure has a wider band gap (0.85 eV). Interestingly, there are superexchange interactions between metal atoms in the MSi6 systems, which result in the AFM alignments.

[Intrapulmonary bronchogenic cysts]

INTRODUCTION

Bronchogenic cysts are congenital malformations that are usually located in the mediastinum. Intrapulmonary location is rare.

OBSERVATION

Four cases of intrapulmonary bronchogenic cysts are reported in order to discuss their clinical and radiological presentation and their treatment.

CONCLUSION

Intrapulmonary bronchogenic cysts diagnostic is often missed. This condition must however be known so as to foresee a resection in order to prevent a potential complication.

Ab Initio Investigation of O-H Dissociation from the Al-OH2 Complex Using Molecular Dynamics and Neural Network Fitting

The dissociation dynamics of the O-H bond in Al-OH2 is investigated on an approximated ab initio potential energy surface (PES). By adopting a dynamic sampling method, we obtain a database of 92 834 configurations. The potential energy for each point is calculated using MP2/6-311G (3df, 2p) calculations; then, a 60-neuron feed-forward neural network is utilized to fit the data to construct an analytic PES. The root-mean-square error (rmse) for the training set is reported as 0.0036 eV, while the rmse for the independent testing set is 0.0034 eV. Such excellent fitting accuracy indeed confirms the reliability of the constructed PES. Subsequently, quasi-classical molecular dynamics (MD) trajectories are performed on the constructed PES at various levels of vibrational excitation in the range of 1.03 to 2.23 eV to investigate the probability of O-H bond dissociation. The results indicate a linear relationship between reaction probability and internal energy, from which we can determine the minimum activation internal energy required for the dissociation as 0.62 eV. Moreover, the O-H bond rupture is shown to be highly correlated with the formation of Al-O bond.

A first-principles investigation of various gas (CO, H2O, NO, and O2) absorptions on a WS2 monolayer: stability and electronic properties

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.

The semi-sewer river: hydraulic backwater effects and combined sewer overflow reverse flows in Central Brussels reduce deoxygenation impact further downstream

In 2011 and 2012 the dissolved oxygen content in the low-discharge river Zenne was monitored continuously, every 5 minutes, downstream of Brussels city centre, making it possible to document the complex mechanisms by which combined sewer overflow (CSO) spills affect both the hydraulics and the oxygen balance of the hydrosystem. In addition to oxygen demand impacts, proportions of water volumes are such that the oxygen-devoid sewage water discharged from CSOs contributes significantly to the oxygen deficit observed in the river further downstream. It is shown that ensuing unexpected hydraulic behaviour, such as a full river-flow reversal, can explain the dual nature of oxygen sag following major CSO events. At times the semi-sewer river plays the role of an in-stream stormwater tank, effectively attenuating the environmental impacts of Brussels CSOs.

Anatase-rutile phase transformation of titanium dioxide bulk material: a DFT + U approach

The anatase-rutile phase transformation of TiO(2) bulk material is investigated using a density functional theory (DFT) approach in this study. According to the calculations employing the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with the Vanderbilt ultrasoft pseudopotential, it is suggested that the anatase phase is more energetically stable than rutile, which is in variance with the experimental observations. Consequently, the DFT + U method is employed in order to predict the correct structural stability in titania from electronic-structure-based total energy calculations. The Hubbard U term is determined by examining the band structure of rutile with various values of U from 3 to 10 eV. At U = 5 eV, a theoretical bandgap for rutile is obtained as 3.12 eV, which is in very good agreement with the reported experimental bandgap. Hence, we choose the DFT + U method (with U = 5 eV) to investigate the transformation pathway using the newly-developed solid-state nudged elastic band (ss-NEB) method, and consequently obtain an intermediate transition structure that is 9.794 eV per four-TiO(2) above the anatase phase. When the Ti-O bonds in the transition state are examined using charge density analysis, seven Ti-O bonds (out of 24 bonds in the anatase unit cell) are broken, and this result is in excellent agreement with a previous experimental study (Penn and Banfield 1999 Am. Miner. 84 871-6).

Prediction of Dispersion Forces: Is There a Problem?

We discuss the ability of a number of standard and non-standard computational techniques to reproduce dispersion forces, using examples from the literature as well as some new examples. We conclude that there are still some cases where standard methods are not so far successful. There are some promising directions under study, however. Manuscript received: 15 March 2001 Final version: 26 October 2001.

Endogenously expressed estrogen receptor and coactivator AIB1 interact in MCF-7 human breast cancer cells

Coactivators are believed to mediate estrogen-induced gene responses via interaction with estrogen receptors (ER). Currently, a major challenge is to determine the importance of each coactivator in a specific cell type and promoter context in response to a particular ligand. The potential of ER to interact with a growing list of coactivators has been shown in a variety of in vitro and gene transfer assays, yet very few data have demonstrated the interaction of endogenous coactivators with ER in intact cells. We report here a ligand-specific interaction of endogenous human ER (hER) and the AIB1 coactivator in MCF-7 human breast cancer cells by using immunoprecipitation analyses. Complexes between endogenously expressed hER and AIB1 were detected in estradiol-treated cells and to a much lesser extent in cells treated with the partial agonist, monohydroxytamoxifen. We were unable to detect an hER-SRC-1 complex in our immunoprecipitations from MCF-7 cells. The in vitro-binding affinity for mouse ER interaction with AIB1 was estimated to be 40-120 nM. We conclude that AIB1 is a major coactivator for hER in MCF-7 human breast cancer cells.

Some Experimental Prospects involving Parabolic Quantum Wells

We discuss two possible lines of experimental investigation based on parabolic quantum wells. In the first proposal, we note that the Generalised Kohn Theorem/Harmonic Potential Theorem forbids electron–electron damping of the Kohn mode in an electron layer gas under strictly parabolic confinement. This applies even for very strong driving. It is therefore interesting to attempt reduction of other sources of broadening in GaAlAs parabolic wells, so as to achieve a prominent narrow resonance in the far infrared. We concentrate here on phononic bandgap structures, which may be of interest for reduction of phonon effects in other systems as well. The second class of proposed experiment involves twinned parabolic wells in an attempt to observe van der Waals forces directly in GaAlAs systems. In a first approximation, the parabolic or Hooke's-law nature of the confinement allows one to use the well as a kind of spring balance to measure the weak van der Waals force. The influence of an applied magnetic field on these forces appears to be significant, and this system might provide the first measurement of such an effect.

Differential detection of N-heterocyclic compounds and their N-methylated derivatives by immunoanalysis

Competitive enzyme-linked immunosorbent assay (ELISA) systems are proposed for the indirect monitoring of formaldehyde by the parallel detection of its N-methylated precursors and the corresponding demethylated compounds. As an example for such immunoanalytical differentiation between an N-heterocyclic compound and its N-methylated derivative, the quantitative detection of the systemic triazole fungicide, myclobutanil, is discussed. Antibodies recognizing the non-zwitterionic structure of 2-(4-chlorophenyl)-2-[(1,2,4-triazol-1-yl)-methyl]-hexanonitril e (myclobutanil) showed only minor binding to corresponding N-alkylated derivatives of myclobutanil. And vice versa, literature data indicate that antibodies raised against the pyridilium ionic structure of the herbicide paraquat, displayed only mediocre reactivity towards the corresponding dealkylated derivatives. Thus, both experimental and literature data suggest that immunoanalytical methods for differential detection of N-methylated heterocycles (potentially including formaldehyde precursors) and their non-methylated counterparts are possible to develop.