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Fentanyl (FTN) and synthetic analogs of FTN continue to ravage populations across the globe, including in the United States where opioids are increasingly being used and abused and are causing a staggering and growing number of overdose deaths each year. This growing pandemic is worsened by the ease with which FTN can be derivatized into numerous derivatives. Understanding the chemical properties/behaviors of the FTN class of compounds is critical for developing effective chemical detection schemes using nanoparticles (NPs) to optimize important chemical interactions. Halogen bonding (XB) is an intermolecular interaction between a polarized halogen atom on a molecule and e−-rich sites on another molecule, the latter of which is present at two or more sites on most fentanyl-type structures. Density functional theory (DFT) is used to identify these XB acceptor sites on different FTN derivatives. The high toxicity of these compounds necessitated a "fragmentation" strategy where smaller, non-toxic molecules resembling parts of the opioids acted as mimics of XB acceptor sites present on intact FTN and its derivatives. DFT of the fragments' interactions informed solution measurements of XB using 19F NMR titrations as well as electrochemical measurements of XB at self-assembled monolayer (SAM)-modified electrodes featuring XB donor ligands. Gold NPs, known as monolayer-protected clusters (MPCs), were also functionalized with strong XB donor ligands and assembled into films, and their interactions with FTN "fragments" were studied using voltammetry. Ultimately, spectroscopy and TEM analysis were combined to study whole-molecule FTN interactions with the functionalized MPCs in solution. The results suggested that the strongest XB interaction site on FTN, while common to most of the drug's derivatives, is not strong enough to induce NP-aggregation detection but may be better exploited in sensing schemes involving films. [ABSTRACT FROM AUTHOR]

Dependence on petroleum and petrochemical products is unsustainable; it is both a finite resource and an environmental hazard. Biodiesel has many attractive qualities, including a sustainable feedstock; however, it has its complications. The pyrolysis (a process already in common use in the petroleum industry) of biodiesel has demonstrated the formation of smaller hydrocarbons comprising many petrochemical products but experiments suffer from difficulty quantifying the myriad reaction pathways followed and products formed. A computational simulation of pyrolysis using "ab initio molecular dynamics" offers atomic-level detail of the reaction pathways and products formed. Herein, the most prevalent fatty-acid ester (methyl linoleate) from the most prevalent feedstock for biodiesel in the United States (soybean oil) is studied. Temperature acceleration within the atom-centered density matrix propagation formalism (Car–Parrinello) utilizing the D3-M06-2X/6-31+G(d,p) model chemistry is used to compose an ensemble of trajectories. The results are grounded in comparison to experimental studies through agreement in the following: (1) the extent of reactivity (40% in the experimental and 36.1% in this work), (2) the homology of hydrocarbon products formed (wt % of C6–C10 products), and (3) the CO/CO2 product ratio. Deoxygenation pathways are critically analyzed (as the presence of oxygen in biodiesel represents a disadvantage in its current use). Within this ensemble, deoxygenation was found to proceed through two subclasses: (1) spontaneous deoxygenation, following one of four possible pathways; or (2) induced deoxygenation, following one of three possible pathways. [ABSTRACT FROM AUTHOR]

The hydrogen storage capacity of a novel permeable material viz Yttrium (Y) decorated zeolite templated carbon (ZTC) has been investigated using ab-initio DFT based simulations. The study reveals that each Y atom bonded on ZTC can attach at the most of 7H 2 molecules with average binding energy of −0.35 eV/H 2. The gravimetric hydrogen storage capacity of ZTC with full decoration of Y atom comes about to 8.61 wt% which is sufficiently higher than the limit of 6.5 wt% set by the energy department of the United States of America. The desorption temperature of the system is 437 K. The stability of the structure over such an elevated temperature has been ensured via molecular dynamics (MD) simulations. The stability of the structure at room temperature and presence of sufficient energy barrier for the diffusion of Y atom signifies that the chances of metal-metal clustering are negligible. It has been discerned that it is the Kubas interaction which plays the key role in the interaction between Y and H 2 molecules. The outcomes show that ZTC adorned with Y is a capable material for hydrogen storage which will inspire the instrumentalists to fabricate ZTC based fuel cell device. [Display omitted] • Y attached on ZTC can adsorb 7H 2 with BE of ∼ −0.35 eV/H 2 leading to 8.61 wt% of H 2. • Almost uniform desorption temperature of 437 K, ideal for fuel cell applications. • The system qualifies for integrity at high temperature. • The system also avoids metal-metal clustering. • The system can act as high capacity reversible hydrogen storage device. [ABSTRACT FROM AUTHOR]

Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 – x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 – x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGA-PBE) and Becke–Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 – x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 –x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 –x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGAPBE) and Becke-Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 –x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

Here, CO gas environment has been used for reduction of graphene oxide (GO) and Pd precursor for preparation of varieties of Pd Nanostructures (PdNSs) with different shapes, size and surface morphologies on graphene support (RG-PdNSs). The extensive ab-initio Molecular Dynamics (MD) simulations and electronic structure calculations have been carried to get theoretical insight for the reduction process of GO by CO. The reduction of GO by CO as observed in experiment are confirmed by ab-initio MD snapshots at different time steps, energetic of the process and the Partial Density of States character of O2p orbital of GO before and after interaction with CO. The discrete states in the Partial Density of States of O2p orbital after CO attack indicates detachment of O from GO. The as-prepared RG-PdNSs are thoroughly characterized by different techniques. The simulation reveals the change in electronic properties from semi-metallic in pristine graphene to metallic due to the attachment of Pd in RG-PdNSs. The electrocatalytic activity of the as-synthesized nanostructures has been investigated toward the multi-functional energy conversion applications, the methanol oxidation reaction, formic acid oxidation reaction and oxygen reduction reaction. The RG-PdNSs exhibit excellent electrocatalytic performance compared to that of unsupported PdNSs and commercial Pd/C. Image 1 [ABSTRACT FROM AUTHOR]

The structural, electronic and elastic properties of LaNi 5− x Fe x (x = 0.25, 0.5, 0.75, 1, 1.25) have been investigated employing the density functional theory with the generalized gradient approximation (GGA). The optimized results indicate that Fe prefers to substitute Ni atom in the 3 g site, and Fe replaces 2c site of Ni atom up to x = 1.25. The radius of 6 m interstitial site gradually increases as x goes from 0 to 1.25 due to volume expansion, which is one of the reasons for the increase of hydrogen storage. Combined with elastic constants and elastic modulus, the anti-pulverization ability of the La–Ni–Fe system enhances, and LaNi 4.25 Fe 0.75 has the best anti-pulverization capability among six crystal structures. According to the density of states, the new peak appears at near −5 eV which is dominated by Fe-3d States. Based on the analysis of charge distributions and charge density differences, the sequence of interaction between atoms is Ni 2 c -Fe 3 g > Ni 2 c -Ni 3 g > Ni 3 g -Ni 3 g > Ni 3 g -Fe 3 g > La–Ni 2 c > La–Fe 2 c , while that of the interactions with H atom is as follows: Fe > Ni 3 g > Ni 2 c > La. The electron hybridization of H and La, Ni, Fe atoms form covalent bonds through electron transfer. To study the interaction between Ni, Fe and H atoms, the electronic densities on (0002) plane for LaNi 4.25 Fe 0.75 are plotted in Figure (a). It is obvious that the charge of H atoms overlaps well with that of iron and nickel atoms, and the corresponding electron density between H atom and Ni, Fe atoms is 0.0864, 0.0868 e/bohr3, respectively. It indicates that the chemical bond between H atom and Fe atom is the strongest, which is still shown that La-Ni-Fe system has the good hydrogen fixation capacity.To analyze the electron transfer behavior and bonding features between atoms, the (0002) plane of charge density difference contour is drawn in Figure (b). It is obvious that hydrogen gains electrons while other atoms lose electrons. Generally, the covalent bonds between H and Fe, Ni are formed. Image 1 • Fe prefers to substitute Ni atom in the 3g site, and Fe is replacing 2c site of Ni atom up to x=1.25. • The radius of 6m interstitial site increases gradually as x goes from 0 to 1.25. • The sequence of interaction between atoms is Ni 2c -Fe 3g > Ni 2c -Ni 3g > Ni 3g -Ni 3g > Ni 3g -Fe 3g > La-Ni 2c > La-Fe 2c , and the order of the interactions with H atom is as follows: Fe > Ni 3g > Ni 2c > La. • The elastic constants for LaNi 5-x Fe x (x=0.25, 0.5, 0.75, 1, 1.25) have been successfully obtained. • LaNi 4.25 Fe 0.75 has the best anti-pulverization characteristics among all structures. [ABSTRACT FROM AUTHOR]

Ab initio calculations for the Linear Macroscopic Dielectric analyses of CH3NH3BiBr3 and CH3NH3GaBr3 (having 8.33% dopant replacement percentage each) as possible replacements for the Lead based perovskite CH3NH3PbBr3 were done in this work using Perdew-Burke-Ernzerhof functional of Density Functional Theory as implemented by FHI-aims Code. Optimized lattice constants were calculated for CH3NH3BiBr3 and CH3NH3GaBr3 to be 9.10 Å and 8.27 Å respectively. The Lowest Unoccupied Molecular Orbital (LUMO), Highest Occupied Molecular Orbital (HOMO) and calculated band gap, Band Structure and Density of States (DOS) plots were made to analyse the band structures of these crystals and they were found to be metallic with a band gap of 0.00018636 eV and 0.00022286 eV for CH3NH3BiBr3 and CH3NH3GaBr3 respectively. The imaginary and real parts of the inter-band and intra-band contribution to the linear dielectric tensor within the e imagi Random Phase Approximation (RPA) of the optical properties of these perovskites were calculated and an average dielectric tensor of 3.1209467 and 2.789173 was found for CH3NH3BiBr3 and CH3NH3GaBr3 respectively. From the absorption data and dielectric tensor components calculated, both materials have an average absorption peak at frequency of 16.5373nm at 1.006567 MeV, 16.2040nm at 1.227600 MeV respectively, across all cubic planes. [ABSTRACT FROM AUTHOR]

The structure, equation of state, mechanical and vibrational properties of single crystals of ices II, VIII, XI and ice in a previously predicted phase bct-4 are studied within the Hartree-Fock method using the density functional theory (B3LYP hybrid functional) with localized Gaussian atomic orbitals as implemented in the "CRYSTAL14" software package. Calculated lattice parameters, elastic moduli of single crystals, and mechanical parameters of polycrystalline samples are shown to meet the criteria of mechanical stability. Parameters of the Vinet equation of state are obtained. Energy band widths and Mulliken atomic charges are determined using obtained energy and spatial distribution of electrons. The frequencies of long-wave vibrations are calculated and vibrational spectra are constructed. [ABSTRACT FROM AUTHOR]

ABSTRACT Downscaled CMIP5 (Coupled Model Intercomparison Project Phase 5) climate projections of maximum daily temperature from the Downscaled CMIP3 and CMIP5 Climate and Hydrology Projections archive are examined regionally over the southeastern United States. Three measures of model skill (means-based, distribution-based, extreme-based) are utilized to assess the ability of 15 downscaled models to simulate daily maximum temperature observations. A new test is proposed to determine statistical significance of the probability density function-based skill measures. Skill scores are found to be generally high for all three measures throughout the study region, but lower scores are present in coastal and mountainous areas. Application of the significance test shows that while the skill scores may be high, they are not significantly higher than could be expected at random in some areas. The distribution-based skill scores are not significant in much of Florida and the Appalachians. The extreme-based skill scores are not significant in more than 90% of the region for all models investigated. The findings suggest that although the downscaled models have simulated observed means well and are a good match to the entire distribution of observations, they are not simulating the occurrence of extreme (above 90th percentile) maximum daily temperatures. [ABSTRACT FROM AUTHOR]

Overlapping soil moisture time series derived from two satellite microwave radiometers (the Soil Moisture and Ocean Salinity (SMOS) and the Advanced Microwave Scanning Radiometer-Earth Observing System) are used to generate a soil moisture time series from 2003 to 2010. Two statistical methodologies for generating long homogeneous time series of soil moisture are considered. Generated soil moisture time series using only morning satellite overpasses are compared to ground measurements from four watersheds in the U.S. with different climatologies. The two methods, cumulative density function (CDF) matching and copulas, are based on the same statistical theory, but the first makes the assumption that the two data sets are ordered the same way, which is not needed by the second. Both methods are calibrated in 2010, and the calibrated parameters are applied to the soil moisture data from 2003 to 2009. Results from these two methods compare well with ground measurements. However, CDF matching improves the correlation, whereas copulas improve the root-mean-square error. [ABSTRACT FROM AUTHOR]

A new continuum solvation model for density functional theory first-principles simulations is presented in the context of plane wave Car–Parrinello molecular dynamics. The Poisson problem—with dielectric function representing the solvent effects—is solved by a compact finite difference method on a regular grid. The smoothness of the solute–solvent transition, and the density-based solute cavity, provide good numerical properties to the model and allow for total energy calculations, reaction barriers calculations, and energy-conserving molecular dynamics. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]

• The detailed ab-initio electronic structure calculations were carried out on non-centrosymmetric La7Ir3 superconductor. • The theoretical results reveal the mixture of La-5d and Ir-5d orbitals to be responsible for superconductivity in La7Ir3. • Band splitting was caused by both spin-orbit and asymmetric spin-orbit couplings but the latter effect is not enough strong. • The electron-phonon coupling constant λ el-ph ∼ 0.63 was estimated, being in the weak-coupling regime of superconductivity. We have carried out the first-principles calculations of the electronic band structure properties of weakly electron correlated, non-centrosymmetric La 7 Ir 3 superconductor (Tc = 2.25 K). We have utilized the GGA-PBE exchange-correlation functionals, implemented in the FP-LAPW ELK code to determine Electronic bands, Densities of States, Fermi surfaces and Electron localization functions. A comparative analysis of scalar relativistic and fully relativistic results reveals the presence of both asymmetric spin - orbit coupling (ASOC) and ordinary spin-orbit coupling (SOC). We have shown that the ASOC with an energy of Δ E ASOC ≈ 10-60 meV, corresponding to relatively low ratio Δ E ASOC / k B T c ≈ 50-310, which is not high enough to cause deviation of the superconductivity from the standard BCS theory. [ABSTRACT FROM AUTHOR]

RbVO 3 luminescent materials have been successfully prepared by solid-state synthesis. The phase, surface morphology and photoluminescence properties of RbVO 3 have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectrophotometer, respectively. The band structure, Density of States and optical properties of RbVO 3 have been simulated by Materials Studio software based on density functional theory (DFT). According to the experimental results and the First-principles, the electronic structure and optical properties of RbVO 3 were studied. The results show that RbVO 3 crystal has a direct band gap with a band gap of 2.973 eV. Under ultraviolet excitation in the range of 210–390 nm, and the excitation spectrum peak appears at 340 nm. The emission spectrum of RbVO 3 phosphors ranges from 400 to 700 nm, and its peak emission spectrum is near 507 nm, showing white luminescence emission. • RbVO 3 has been successfully prepared by solid-state synthesis. • The RbVO 3 luminescent material is a high brightness phosphor. • PL measurements on RbVO 3 shows a broad emission centered at 507 nm. • The optical properties of RbVO 3 are studied in detail based on first-principles for the first time. • The band structure, density of States and optical properties of RbVO 3 were calculated to reveal its luminescence mechanism. [ABSTRACT FROM AUTHOR]

The removal of fluoride from water using adsorption on a low-cost mineral such as kaolinite is an important research topic. The present communication uses Density Functional Theory (DFT) and Molecular Dynamics (MD) based simulations to comprehensively investigate the adsorption behaviour of HF, one of the most predominant species of fluoride in the aqueous solutions, on the (0 0 1) surface of kaolinite. The optimum geometric configurations of adsorption of HF on different possible sites on the mineral surface have been established, and the corresponding adsorption energies, bond distances, Partial Density of States (PDOS), Mulliken charges and electron density difference plots have been analyzed to understand the interaction at each site. To explore the site-dependent adsorption behaviour, the interaction of HF has been investigated on different sites such as aluminium centres, surface oxygen atoms (both lying and upright) and cavity site (void space encircled by six aluminium centres). The analysis shows that the F atom has a strong tendency to form hydrogen bonds with the surface H atom on kaolinite. Among the three aforementioned types of adsorption sites considered, the "cavity" site is found to offer the greatest adsorption strength. Further, MD simulations have been undertaken to explain the effect of water on the adsorption and substantiate the bonding mechanism. • Adsorption of HF on the kaolinite (0 0 1) surface was investigated by DFT-D simulation. • Optimum adsorption configurations of HF on different possible sites are established. • MD simulations reveal effect of solvent on the behaviour of HF adsorption. • Complex structure, preferred adsorption position and adsorption bonding pattern were solved. • Among all the adsorption sites considered, the "cavity" site is found to offer the greatest adsorption strength. [ABSTRACT FROM AUTHOR]

In the present approach, we have successfully synthesized wormlike Ni 3 S 2 and Ni 3 S 2 -RGO hybrids on nickel (Ni) foam by a facile and highly reproducible one-step chemical vapor deposition (CVD) method. We have demonstrated that Ni 3 S 2 and Ni 3 S 2 -RGO hybrids can be grown directly on the current collector of energy storage devices without using any binder, which may lead to serve industry for large-scale production of the material. We have studied the pseudocapacitive energy storage performance of the CVD grown Ni 3 S 2 and its hybrids with variable concentration of RGO. The Ni 3 S 2 -RGO hybrid with 0.5 mg GO showed a maximum areal specific capacitance of 1.4 F·cm−2 at a current density of 1 mA·cm−2 (approximately 1124 Fg−1 at a current density of 1 Ag−1). The enhanced supercapacitive performance of Ni 3 S 2 -RGO predominantly due to its high surface area and high conductivity as compared to bare Ni 3 S 2. The electrochemical impedance spectroscopic analysis revealed Ni 3 S 2 -RGO possess enhanced charge-transfer characteristics as compared to bare Ni 3 S 2. Furthermore, Density Functional Theory (DFT) simulations infer the strong hybridization between C p orbital and Ni d orbital lead to enhanced electrochemical property and Density of States (DOS) is crucially responsible for the improved charge storage performance of Ni 3 S 2 -RGO hybrids. Unlabelled Image • A naive, convinient, cost effective and less time-consuming CVD based synthesis technique is developed for the synthesis of binder free Ni 3 S 2 /RGO electrode. • Resultant Ni 3 S 2 /RGO hybrid exhibit maximum capacitance of 1124 Fg−1 at a current density of 1 Ag−1. • Cycling stability was good even after 5000 charge/discharge cycles with capacitance retention of 78% of the initial specific capacitance. • Theoretical DFT simulation studies support the experimental data and explain the mechanisms responsible for the enhanced supercapacitor property of Ni 3 S 2 /RGO hybrid. [ABSTRACT FROM AUTHOR]