Theoretical Study on the Structures and Electronic Properties of Tungsten Fluorides at High Pressures.

Transition metal fluorides are a series of strong oxidizing agents. Tungsten (W) fluorides, particularly WF6, have shown broad applications such as luminescence and fluorinating agent. However, other stoichiometries of W fluorides have rarely been studied. It is well-known that pressure can induce structural phase transition, stabilize new compounds, and produce novel properties. In this work, the high-pressure phases of W-F were searched systematically at the pressure range of 0-200 GPa through first-principles swarm-intelligence structural search calculations. A new stoichiometry of WF4 has been predicted to be stable under high pressures. On the other hand, two new high-pressure phases of WF6 with the symmetries of P 2 1 ${{P2}_{1}}$ /m and P ${P}$ -1 were found with decahedral structural units. The electronic properties of the W-F compounds were then investigated. The predicted stable WF6 high-pressure phases maintain semiconducting features, since the W atom provides all its valence electrons to fluorine. We evaluated the oxidizing ability of WF6 by calculating its electron affinity potential. The high pressure P 2 1 ${{P2}_{1}}$ /m WF6 molecular phase shows higher oxidation capacity than the ambient phase. The built pressure-composition phase diagram and the theoretical results of W-F system provide some useful information for experimental synthesis.

Spectrum and mortality of opportunistic infections among HIV/AIDS patients in southwestern China.

We describe the opportunistic infections (OIs) of HIV/AIDS to understand the spectrum, mortality, and frequency of multiple coinfected OIs among HIV/AIDS patients in southern China, where OIs are severe. We carried out a retrospective cohort study of hospitalized HIV-infected individuals at the Fourth People's Hospital of Nanning, Guangxi, China, from Jan. 2011 to May. 2019. The chi-square test was used to analyze cross-infection; the Kaplan‒Meier analysis was used to compare mortality. A total of 12,612 HIV-infected patients were admitted to this cohort study. Among them, 8982 (71.2%) developed one or more OIs. The overall in-hospital mortality rate was 9.0%. Among the patients, 35.6% coinfected one OI, and 64.4% coinfected more than two OIs simultaneously. Almost half of the patients (60.6%) had CD4 + T-cell counts < 200 cells/µL. Pneumonia (39.8%), tuberculosis (35.3%), and candidiasis (28.8%) were the most common OIs. Coinfected cryptococcal meningitis and dermatitis are the most common combined OIs. The rate of anaemia (17.0%) was highest among those common HIV-associated complications. Multiple OIs are commonly found in hospitalized HIV/AIDS patients in southwestern China, which highlights the need for improved diagnosis and treatment.

Achieving high quantum capacitance graphdiyne through doping and adsorption.

In recent years, a new two-dimensional carbon material, graphdiyne (GDY), has attracted extensive attention in the field of energy storage, due to its unique topological and electronic structures, high charge mobility, and excellent electron transport properties. However, the disappearance of the density of states near the Fermi level leads to a low quantum capacitance (CQ) of pristine GDY, which limits its application in supercapacitors. Here, we propose doping and metal atom adsorption to be efficient ways to increase the CQ of GDY. Based on first-principles density functional theory, the effects of doping B, N, P, and S atoms and adsorbing Au, Ag, Cu, Ti, and Al atoms on the CQ of GDY are systematically investigated. The results show that the CQ of GDY can be significantly improved by introducing doping/adsorption, which could be a potential cathode material and anode material for supercapacitors. Our work provides an effective way for GDY to be applied as an efficient electrode material for supercapacitors.

Emergent superconductivity in TaO3 at high pressures.

Tantalum (Ta) is an interesting transition metal that exhibits superconductivity in its elemental states. Additionally, several Ta chalcogenides (S and Se) have also demonstrated superconducting properties. In this work, we propose the existence of five high-pressure metallic Ta-O compounds (e.g., TaO3, TaO2, TaO, Ta2O, and Ta3O), composed of polyhedra centered on Ta/O atoms. These compounds exhibit distinct characteristics compared to the well-known semiconducting Ta2O5. One particularly interesting finding is that TaO3 shows an estimated superconducting transition temperature (Tc) of 3.87 K at 200 GPa. This superconductivity is primarily driven by the coupling between the low-frequency phonons derived from Ta and the O 2p and Ta 5d electrons. Remarkably, its dynamically stabilized pressure can be as low as 50 GPa, resulting in an enhanced electron-phonon coupling and a higher Tc of up to 9.02 K. When compared to the superconductivity of isomorphic TaX3 (X = O, S, and Se) compounds, the highest Tc in TaO3 is associated with the highest NEF and phonon vibrational frequency. These characteristics arise from the strong electronegativity and small atomic mass of the O atom. Consequently, our findings offer valuable insights into the intrinsic physical mechanisms of high-pressure behaviors in Ta-O compounds.

Metagenomic next-generation sequencing for rapid detection of pulmonary infection in patients with acquired immunodeficiency syndrome.

BACKGROUND: Acquired immunodeficiency syndrome (AIDS) is associated with a high rate of pulmonary infections (bacteria, fungi, and viruses). To overcome the low sensitivity and long turnaround time of traditional laboratory-based diagnostic strategies, we adopted metagenomic next-generation sequencing (mNGS) technology to identify and classify pathogens. RESULTS: This study enrolled 75 patients with AIDS and suspected pulmonary infections who were admitted to Nanning Fourth People's Hospital. Specimens were collected for traditional microbiological testing and mNGS-based diagnosis. The diagnostic yields of the two methods were compared to evaluate the diagnostic value (detection rate and turn around time) of mNGS for infections with unknown causative agent. Accordingly, 22 cases (29.3%) had a positive culture and 70 (93.3%) had positive valve mNGS results (P value < 0.0001, Chi-square test). Meanwhile, 15 patients with AIDS showed concordant results between the culture and mNGS, whereas only one 1 patient showed concordant results between Giemsa-stained smear screening and mNGS. In addition, mNGS identified multiple microbial infections (at least three pathogens) in almost 60.0% of patients with AIDS. More importantly, mNGS was able to detect a large variety of pathogens from patient tissue displaying potential infection and colonization, while culture results remained negative. There were 18 members of pathogens which were consistently detected in patients with and without AIDS. CONCLUSIONS: In conclusion, mNGS analysis provides fast and precise pathogen detection and identification, contributing substantially to the accurate diagnosis, real-time monitoring, and treatment appropriateness of pulmonary infection in patients with AIDS.

Fabrication, Evaluation, and Antioxidant Properties of Carrier-Free Curcumin Nanoparticles.

Curcumin (Cur), a natural hydrophobic polyphenolic compound, exhibits multiple beneficial biological activities. However, low water solubility and relative instability hinder its application in food fields. In this study, carrier-free curcumin nanoparticles (CFC NPs) were prepared by adding the DMSO solution of Cur into DI water under continuous rapid stirring. The morphology of CFC NPs was a spherical shape with a diameter of 65.25 ± 2.09 nm (PDI = 0.229 ± 0.107), and the loading capacity (LC) of CFC NPs was as high as 96.68 ± 0.03%. The thermal property and crystallinity of CFC NPs were investigated by XRD. Furthermore, the CFC NPs significantly accelerated the release of Cur in vitro owing to its improved water dispersibility. Importantly, CFC NPs displayed significantly improved DPPH radical scavenging activity. Overall, all these results suggested that CFC NPs would be a promising vehicle to widen the applications of Cur in food fields.

Pressure-stabilized hexafluorides of first-row transition metals.

Fluorine chemistry was demonstrated to show the importance of stretching the limits of chemical synthesis, oxidation state, and chemical bonding at ambient conditions. Thus far, the highest fluorine stoichiometry of a neutral first-row transition-metal fluoride is five, in VF5 and CrF5. Pressure can stabilize new stoichiometric compounds that are inaccessible at ambient conditions. Here, we attempted to delineate the fluorination limits of first-row transition metals at a high pressure through first-principles swarm-intelligence structure searching simulations. Besides reproducing the known compounds, our extensive search has resulted in a plethora of unreported compounds: CrF6, MnF6, FeF4, FeF5, FeF6, and CoF4, indicating that the application of pressure achieves not only the fluorination limit (e.g., hexafluoride) but also the long-sought bulky tetrafluorides. Our current results provide a significant step forward towards a comprehensive understanding of the fluorination limit of first-row transition metals.

Resilience and intention of healthcare workers in China to receive a COVID-19 vaccination: The mediating role of life satisfaction and stigma.

AIMS: The present study investigated the association between resilience, stigma, life satisfaction and the intention to receive a COVID-19 vaccination among Chinese HCWs. It also explored the mediating role of stigma and life satisfaction on the association between resilience and intention to receive a COVID-19 vaccination. DESIGN: An anonymous cross-sectional survey. METHODS: 1733 HCWs from five hospitals in four provinces of mainland China completed a cross-sectional online survey in October and November 2020. RESULTS: Among the HCWs, the rate of intention to receive a COVID-19 vaccination was 73.1%. Results from structural equation modelling showed that resilience was associated both directly, and indirectly with greater intent to receive a COVID-19 vaccination through two pathways: first by increasing life satisfaction, and second by reducing stigma and increasing life satisfaction. CONCLUSION: Promoting the resilience of HCWs has the potential to increase the COVID-19 vaccination uptake rate among HCWs in China. IMPACT: This study tested the relationship between several psychological factors and the COVID-19 vaccination intention of HCWs in China, finding that resilience played a significant role in improving COVID-19 vaccination intention rates by reducing stigma and increasing life satisfaction.

Prediction of new thermodynamically stable ZnN2O3 at high pressure.

Pressure has become a useful parameter to prepare novel functional materials. Considering the excellent performance of ZnO and Zn3N2 and the formation of strong Zn-O, Zn-N, and N-O bonds in the known compounds, we explored potential Zn-N-O ternary compounds with interesting properties. With the aid of first-principles swarm-intelligence search calculations, we identified a hitherto unknown ZnN2O3 ternary compound with a symmetry of P21. Its remarkable feature is that N pairs interconnect the distorted Zn-centered decahedrons, in which the Zn atom forms bonds with one N and six O atoms. The compression of ZnO + NO2 + N2 might be an easy way to synthesize ZnN2O3. Electronic property calculations disclose that ZnN2O3 is a wide band gap semiconductor with a gap value of 3.48 eV, which is larger than those of ZnO and Zn3N2. Moreover, the high-pressure phase diagram of Zn-N binary compounds was explored with a wide range of chemical compositions. Two metallic N-rich zinc nitrides (e.g., ZnN2 and ZnN4) are proposed, containing intriguing N2 dimers and zigzag N chains. ZnN2 exhibits superconducting properties, and becomes the first example of superconductor in zinc nitrides. Our current results unravel the unusual stoichiometry of Zn-N-O compounds and provide further insight into the diverse electronic properties of zinc nitrides under high pressure.

Unconventional stable stoichiometry of vanadium peroxide.

Peroxides have attracted considerable attention due to their intriguing electronic properties and diverse applications. However, only a few transition metal peroxides have been known thus far, limiting the variety of peroxide examples. Here, we demonstrate the stabilization of peroxides in the O-rich V-O system through first-principles calculations coupled with a swarm-intelligence structure search. As well as reproducing the known stoichiometries of VO, V2O3, VO2, and V2O5, two hitherto unknown V2O and VO4 stoichiometries are predicted to be thermodynamically stable at megabar pressures. VO4 has the highest oxygen content among the known peroxides to date. More interestingly, its electronic band gap increases with pressure, originating from the pressure-induced decrease of O-O bonding length in the peroxide group. V-rich V2O exhibits superconductivity, becoming the first example in the V-O system. Our work not only unravels the unusual vanadium peroxide, but also provides further insight into the diverse electronic properties of vanadium oxides under high pressure.

Exploring the origin of electrochemical performance of Cr-doped LiNi0.5Mn1.5O4.

Discorded LiNi0.5Mn1.5O4 has become a promising candidate for Li ion batteries due to its high specific energy. However, its poor structural stability restricts its practical application. After extensive exploration, Cr-doped disordered LiNi0.5Mn1.5O4 demonstrates enhanced structural stability and electrochemical performance. Thus far, its origin at the electronic structural level remains elusive, which is important to further performance improvement. First-principles calculations disclose that a Cr atom prefers to substitute Ni rather than a Mn atom. The transferred charge from Cr to Mn induces the reduction of Mn ions and lengthens the Li-O bond distance, which are mainly responsible for the lower Li ion diffusion energy barrier and Li vacancy formation energy. The heavy oxidation of O ions is a main factor to induce the structural degeneration. In this case, the reduced Mn ion delays the oxidation of the O ion, enhancing the structural stability. In addition, Cr doping increases the thermodynamic stability of intermediate phases during delithiation, decreasing the structural strain in the delithiation process. Ordered and disordered LiNi0.5Mn1.5O4 are also included for comparison. Our work provides an opportunity to fully understand Cr-doped LiNi0.5Mn1.5O4 at the atomic scale.

Preparation of a novel Ni-MOF and porous graphene aerogel composite and application for simultaneous electrochemical determination of nitrochlorobenzene isomers with partial least squares.

Metal-organic framework Ni2(BDC)2(DABCO) (Ni-MOF)/porous graphene aerogel (PGA) composites were fabricated for the first time. The introduction of PGA enhances conductivity of Ni-MOF, prevents Ni-MOF from accumulating, reduces the size of Ni-MOF, and increases the pore size of composites, which improve the electrocatalytic activity of Ni-MOF@PGA-2. The prepared sensors based on Ni-MOF@PGA-2 composite show the highest catalytic current towards electroreduction of 2-nitrochlorobenzene (2-NCB), 3-nitrochlorobenzene (3-NCB), and 4-nitrochlorobenzene (4-NCB) at around - 0.61 V, - 0.56 V, and - 0.57 V (vs. Ag/AgCl) with respect to other sensors. The reaction mechanisms also are discussed. Under optimized experiment conditions, the Ni-MOF@PGA-2/GCE displays the widest linear range (6-1260, 4-980, and 2-1280 µM for 2-NCB, 3-NCB, and 4-NCB, respectively) for determination of individual nitrochlorobenzene isomers (NCBIs) compared to that of recent reports, and relatively low detection limit (0.093, 0.085, and 0.051 µM for 2-NCB, 3-NCB, and 4-NCB, respectively). More importantly, three NCBIs in the mixture were for the first time simultaneously determined by combining differential pulse voltammetry (DPV) based on Ni-MOF@PGA-2/GCE with partial least squares (PLS) chemometrics modeling method. The proposed method was evaluated towards the determination of NCBI mixtures in tap water and Jing lake water, and satisfactory recoveries were obtained. Graphical abstract.

Exploring the Limits of Transition-Metal Fluorination at High Pressures.

Fluorination is a proven method for challenging the limits of chemistry, both structurally and electronically. Here we explore computationally how pressures below 300 GPa affect the fluorination of several transition metals. A plethora of new structural phases are predicted along with the possibility for synthesizing four unobserved compounds: TcF7 , CdF3 , OsF8 , and IrF8 . The Ir and Os octaflourides are both predicted to be stable as quasi-molecular phases with an unusual cubic ligand coordination, and both compounds formally correspond to a high oxidation state of +8. Electronic-structure analysis reveals that otherwise unoccupied 6p levels are brought down in energy by the combined effects of pressure and a strong ligand field. The valence expansion of Os and Ir enables ligand-to-metal F 2p→M 6p charge transfer that strengthens M-F bonds and decreases the overall bond polarity. The lower stability of IrF8 , and the instability of PtF8 and several other compounds below 300 GPa, is explained by the occupation of M-F antibonding orbitals in octafluorides with a metal-valence-electron count exceeding 8.

IrF8 Molecular Crystal under High Pressure.

An important goal in chemistry is to prepare F-rich transition metal fluorides due to the high oxidation states and potential applications such as oxidating and fluorinating agents. Thus far, the highest F stoichiometry in the neutral transition metal fluorides is 7. Here, we identify a hitherto unknown IrF8 compound through first-principles swarm-intelligence structure search calculations under high pressure. The three identified IrF8 phases exhibit typical molecular crystal characters, showing +8 oxidation state in Ir. The spatial symmetry of the basic building block in the three IrF8 phases gradually increases with pressure (e.g., dodecahedron [Formula: see text] square antiprism [Formula: see text] quasicube). The pressure-induced faster increase of Ir 5d orbital energy level with respect to F 2p provides a strong charge transfer driving force from Ir 5d to F 2p, facilitating the formation of F-rich compounds. More interestingly, the predicted electron affinities of the three predicted IrF8 phases are comparable/larger than that of PtF6, the strongest oxidation agent in the third row transition metal hexafluorides. The built high-pressure phase diagram of Ir-F binary compounds provides useful information for experimental synthesis.

Two-Dimensional PC6 with Direct Band Gap and Anisotropic Carrier Mobility.

Graphene and phosphorene are two major types of atomically thin two-dimensional materials under extensive investigation. However, the zero band gap of graphene and the instability of phosphorene greatly restrict their applications. Here, we make first-principle unbiased structure search calculations to identify a new buckled graphene-like PC6 monolayer with a number of desirable functional properties. The PC6 monolayer is a direct-gap semiconductor with a band gap of 0.84 eV, and it has an extremely high intrinsic conductivity with anisotropic character (i.e., its electron mobility is 2.94 × 105 cm2 V-1 s-1 along the armchair direction, whereas the hole mobility reaches 1.64 × 105 cm2 V-1 s-1 along the zigzag direction), which is comparable to that of graphene. On the other hand, PC6 shows a high absorption coefficient (105 cm-1) in a broad band, from 300 to 2000 nm. Additionally, its direct band gap character can remain within a biaxial strain of 5%. All these appealing properties make the predicted PC6 monolayer a promising candidate for applications in electronic and photovoltaic devices.

Gold with +4 and +6 Oxidation States in AuF4 and AuF6.

An important goal in chemistry is to prepare compounds with unusual oxidation states showing exciting properties. For gold (Au), the relativistic expansion of its 5d orbitals makes it form high oxidation state compounds. Thus far, the highest oxidation state of Au known is +5. Here, we propose high pressure as a controllable method for preparing +4 and +6 oxidation states in Au via its reaction with fluorine. First-principles swarm-intelligence structure search identifies two hitherto unknown stoichiometric compounds, AuF4 and AuF6, exhibiting typical molecular crystal character. The high-pressure phase diagram of Au fluorides is rather different from Cu or Ag fluorides, which is indicated by stable chemical compositions and the pressures needed for the synthesis of these compounds. This difference can be associated with the stronger relativistic effects in Au relative to Cu or Ag. Our work represents a significant step forward in a more complete understanding of the oxidation states of Au.

Eliciting promises from children reduces cheating.

Widespread cheating can undermine rules that are necessary for maintaining social order. Preventing cheating can be a challenge, especially with regard to children, who as a result of their limited executive function skills may have particular difficulty with resisting temptation to cheat. We examined one approach designed to help children resist this temptation: eliciting a verbal commitment to not cheat. We tested 4- to 7-year-olds (total N = 330) and found that starting at 5 years of age, a verbal commitment to not cheat led to a substantial reduction in cheating. The results suggest that verbal commitments can be used to help children overcome temptations and comply with rules.

Theoretical Studies on the Quantum Capacitance of Two-Dimensional Electrode Materials for Supercapacitors.

In recent years, supercapacitors have been widely used in the fields of energy, transportation, and industry. Among them, electrical double-layer capacitors (EDLCs) have attracted attention because of their dramatically high power density. With the rapid development of computational methods, theoretical studies on the physical and chemical properties of electrode materials have provided important support for the preparation of EDLCs with higher performance. Besides the widely studied double-layer capacitance (CD), quantum capacitance (CQ), which has long been ignored, is another important factor to improve the total capacitance (CT) of an electrode. In this paper, we survey the recent theoretical progress on the CQ of two-dimensional (2D) electrode materials in EDLCs and classify the electrode materials mainly into graphene-like 2D main group elements and compounds, transition metal carbides/nitrides (MXenes), and transition metal dichalcogenides (TMDs). In addition, we summarize the influence of different modification routes (including doping, metal-adsorption, vacancy, and surface functionalization) on the CQ characteristics in the voltage range of ±0.6 V. Finally, we discuss the current difficulties in the theoretical study of supercapacitor electrode materials and provide our outlook on the future development of EDLCs in the field of energy storage.

Effect of modulation by adsorption and doping on the quantum capacitance of borophene.

Electric double-layer supercapacitors (EDLCs) have attracted much attention in the energy storage field due to their advantages such as high output power, long service life, safety and high efficiency. However, their low energy density limits their application. Aiming at the problem of the low energy density of EDLCs, improving quantum capacitance (CQ) of electrode materials is an effective strategy. In this paper, we systematically studied the effects of vacancy, doping, and metal atom adsorption on the CQ of borophene using first-principles calculations. The results show that S and N doping greatly enhance the charge accumulation of borophene at positive and negative potential, respectively. The maximum CQ values of S-doped and N-doped borophene are 157.3 µF cm-2 (0.38 V) and 187.8 µF cm-2 (-0.24 V), respectively. Both of them can serve as ideal candidates for the positive (S-doped one) and negative (N-doped one) electrodes of EDLCs. Besides, metal Al atom-adsorbed borophene can also effectively enhance the CQ, with a maximum value of 109.1 µF cm-2.

Molecular dynamics study of fluorosulfonyl ionic liquids as electrolyte for electrical double layer capacitors.

The development of high-performance supercapacitors is an important goal in the field of energy storage. Ionic liquids (ILs) are promising electrolyte materials for efficient energy storage in supercapacitors, because of the high stability, low volatility, and wider electrochemical stability window than traditional electrolytes. However, ILs-based supercapacitors usually show a relatively lower power density owing to the inherent viscosity-induced low electrical conductivity. Fluorosulfonyl ILs have aroused much attention in energy storage devices due to its low toxicity and excellent stability. Here, we propose that structural modification is an effective way to improve the energy storage performance of fluorosulfonyl ILs through the classical molecular dynamics (MD) method. Four fluorosulfonyl ILs with different sizes and symmetries were considered. Series of properties including conductivity, interface structure, and double-layer capacitance curves were systematically investigated. The results show that smaller size and more asymmetric structure can enhance self-diffusion coefficient and conductivity, and improve the electrochemical performance. Appropriate modification of the electrodes can further enhance the capacitive performance. Our work provides an opportunity to further understand and develop the fluorosulfonyl ILs electrolyte in supercapacitors.