DFT Results Research Articles

New Epoxy sugar based glucose derivatives as eco friendly corrosion inhibitors for the carbon steel in 1.0 M HCl: Experimental and theoretical investigations

In this study, we chose to synthesize new sugar based glucose derivatives as ecological corrosion inhibitors for carbon steel in acidic medium. The products obtained in the form of syrupy liquids, and the purity of obtained compounds was characterized by NMR spectroscopy analysis. The corrosion inhibition activities for both compounds were evaluated by electrochemical and rheological methods. Thus, the results of the experimental tests have been confirmed by theoretical studies ( DFT , MC and MD simulations). The surface study of carbon steel has been characterized by the scanning electron spectroscopy ( SEM ). The gravimetric solutions were identified using UV-Vis spectroscopy and Inductively Coupled Plasma-Optical Spectroscopy ( ICP-OES ). • Newly both glucose derivatives was synthesized and evaluated as corrosion inhibitor for steel in acidic medium. • Adsorption of G-C 12 and G-C 6 , obeyed the Langmuir adsorption isotherm model their adsorption was supported by SEM and UV-vis spectroscopic analyses. • The experimental results were correlated with DFT and MC stimulation results.

The recovery of strontium from acidic medium using novel strontium selective extractant: An experimental and DFT study

In view of the limited solvent system known for the Sr2+ extraction from acidic media, extraction and recovery of 90Sr from acidic medium using novel Octabenzyloxyoctakis[[[(N,N-diethylamino)carbonyl)]methyl]oxy]calix[8]arene (BOC8A) extractant in nitro alkane medium are presented in this paper. BOC8A and nitro alkanes have been synthesized and characterized by 1H NMR, 13C NMR, FTIR and GC–MS techniques. Solvent composition of 0.01 M BOC8A in nitro octane (NO) has been optimized for substantial amount of extraction of strontium from feed acidity of 3.5−4 M nitric acid, (D3.5−4 M HNO3 = 7.1–7.8). Poor extraction of Pu4+, Ba2+, Na+ and UO22+ and negligible extraction of Am3+, Cs+, Ru3+, Nd3+, Zr2+ and trivalent lanthanides are observed. Ion dissociation mechanism was found to be operative involving an extractable complex having Sr2+, BOC8A and HNO3 in a ratio of 1:1:2. About 99 % of Sr2+ from the loaded solvent was recovered with 0.01 M HNO3. DFT calculations were used to predict the structures of free, protonated BOC8A and its complex with Sr2+. DFT result showed reorientation in conformation of BOC8A due to protonation resulting in the Sr2+ extraction from acidic medium with significantly high interaction energy between Sr2+ and diprotonated form of BOC8A.

Hydrogen in zirconium: Atomistic simulations of diffusion and interaction with defects using a new embedded atom method potential

A new interatomic embedded atom method (EAM) potential, called BMD19, has been developed for simulations of hexagonal zirconium with dissolved hydrogen. The parameters are fitted to data from density functional calculations and calibrated using the experimental room-temperature density of zirconium. The new potential overcomes the unphysical negative thermal expansion coefficient between 0 and 200 K obtained with the frequently used Mendelev-Ackland potential (MA#3). It reproduces the geometry around self-interstitial atoms (SIA’s) obtained with DFT while the MA#3 and the COMB3 potentials yield structures with the SIA between basal planes. The energies of forming vacancies and self-interstitials as well as the elastic coefficients are of similar quality for all potentials investigated in the present work. Compared with DFT results, the new potential describes the interactions of H with Zr better overall than any previously published interatomic potentials. This includes the binding energy of interstitial H and its dependence on lattice strain for tetrahedral and octahedral sites, the trapping energy in vacancies, surface segregation energy, and the energy of diffusion barriers. The present work illustrates the usefulness of the BMD19 potential by showing the dependence of diffusion coefficients on lattice strain, the accumulation of H in vacancy c-loops and by correctly describing the Soret effect, i.e. the diffusion of H from hotter to colder regions of the material. Simulations of the effect of grain boundaries and internal surfaces (e.g. nano-voids) and diffusion on surfaces provide further demonstrations of the usefulness of this new potential.

Strain-Modulated Platinum-Palladium Nanowires for Oxygen Reduction Reaction.

Electrocatalytic activity of alloy nanocatalytsts can be manipulated effectively by tuning their physical properties (ensemble, geometric, and ligand effects) to afford optimal surface structure and compositions for proton exchange membrane fuel cell (PEMFC) application. Herein, highly catalytic platinum-palladium nanowires (PtnPd100-n NWs) with a subtle lattice strain and Boerdijk-Coxeter helix type morphology are synthesized through a surfactant-free, thermal single phase solvent method. X-ray diffraction results show that PtnPd100-n NWs are exposed through the (111) facets and their shrinking or expanding lattice parameters can be modulated by the alloy compositions. Electrochemical results reveal that their high catalytic activity correlates with the lattice shrinking, facets, and bimetallic compositions, showing higher activity when the ratio of Pt and Pd is ∼78:22, which is further supported by DFT results. Compared to the nanoparticle type platinum-palladium alloyed catalysts with similar metal compositions (PtnPd100-n NPs), the PtnPd100-n NWs exhibit significantly improved electrocatalytic activity and stability for the oxygen reduction reaction. These findings open new strategies to design the highly active and stable alloy nanocatalysts with controllable compositions.

Synthesis and Tunable Optical Properties of C,N-Chelated Borate Luminophores Derived from Potassium Acyltrifluoroborates.

A new class of borate luminophores has been synthesized by a simple two-step reaction using potassium acyltrifluoroborates (KATs) as starting materials. The hydrazones obtained from reactions between KATs and 2-hydrazinopyridines followed by a cyclization resulted in the unprecedented formation of C,N-chelated six-membered bora-heterocycles. Under consideration of the results of DFT and TD-DFT calculations, four luminophores based on such bora-heterocycles are designed and synthesized, which exhibit a tunable fluorescence range from blue to red in the solid state. Moreover, one of the luminophores exhibits mechanofluorochromism from blue to yellow/green. As a result of the aforementioned mechanochromism of one of these luminophores, white-color emission was achieved by simply mixing the four luminophores.

Polyfuran-based chemical sensors: reactivity analysis via Fukui indexes and reactive molecular dynamics

ABSTRACTIn the present study we employ electronic structure calculations (based on Density Functional Theory -DFT approach) and Fully Atomistic Reactive Molecular Dynamics (FARMD) simulations (based on ReaxFF reactive force field) to evaluate the reactivity of branched polyfuran (PF) derivatives and identify promising systems for chemical sensing. Condensed-to-atoms Fukui indexes (CAFI) were employed to identify the most reactive sites on the oligomers structure. The chemical sensing abilities of the most promising systems were evaluated via FARMD simulations in the presence of distinct gaseous compounds. The results indicate the derivatives PF-CCH and PF-NO₂ (i.e. CCH and NO2 as side groups) as the most promising systems for chemical sensor applications, presenting higher reactivity on the most accessible sites. An interesting correspondence between DFT and MD results was also identified, suggesting the plausibility of using CAFI parameters for the identification of improved materials for chemical sensors.

Theoretical Description of R-X⋯NH3 Halogen Bond Complexes: Effect of the R Group on the Complex Stability and Sigma-Hole Electron Depletion.

In the present work, a number of R–X⋯NH3 (X = Cl, Br, and I) halogen bonded systems were theoretical studied by means of DFT calculations performed at the ωB97XD/6-31+G(d,p) level of theory in order to get insights on the effect of the electron-donating or electron-withdrawing character of the different R substituent groups (R = halogen, methyl, partially fluorinated methyl, perfluoro-methyl, ethyl, vinyl, and acetyl) on the stability of the halogen bond. The results indicate that the relative stability of the halogen bond follows the Cl < Br < I trend considering the same R substituent whereas the more electron-withdrawing character of the R substituent the more stable the halogen bond. Refinement of the latter results, performed at the MP2/6-31+G(d,p) level showed that the DFT and the MP2 binding energies correlate remarkably well, suggesting that the Grimme’s type dispersion-corrected functional produces reasonable structural and energetic features of halogen bond systems. DFT results were also observed to agree with more refined calculations performed at the CCSD(T) level. In a further stage, a more thorough analysis of the R–Br⋯NH3 complexes was performed by means of a novel electron localization/delocalization tool, defined in terms of an Information Theory, IT, based quantity obtained from the conditional pair density. For the latter, our in-house developed C++/CUDA program, called KLD (acronym of Kullback–Leibler divergence), was employed. KLD results mapped onto the one-electron density plotted at a 0.04 a.u. isovalue, showed that (i) as expected, the localized electron depletion of the Br sigma-hole is largely affected by the electron-withdrawing character of the R substituent group and (ii) the R–X bond is significantly polarized due to the presence of the NH3 molecule in the complexes. The afore-mentioned constitutes a clear indication of the dominant character of electrostatics on the stabilization of halogen bonds in agreement with a number of studies reported in the main literature. Finally, the cooperative effects on the [Br—CN]n system (n = 1–8) was evaluated at the MP2/6-31+G(d,p) level, where it was observed that an increase of about ~14.2% on the complex stability is obtained when going from n = 2 to n = 8. The latter results were corroborated by the analysis of the changes on the Fermi-hole localization pattern on the halogen bond zones, which suggests an also important contribution of the electron correlation in the stabilization of these systems.

The DFT Quest for Possible Reaction Pathways, Catalytic Species, and Regioselectivity in the InCl3-Catalyzed Cycloaddition of N-Tosyl Formaldimine with Olefins or Allenes.

The present work focuses on a theoretical investigation of the plausible mechanism, determination of catalytically active species, and understanding of the regioselectivity in the InCl3-catalyzed cycloaddition of N-tosyl formaldimine with alkenes or allenes. InCl3 and InCl2+ coordinated by dichloroethane (InCl2+-DCE) were investigated as model catalytic systems. DFT data supported that InCl2+-DCE represent the plausible in situ generated catalytic species. The catalytic cycle starts from the coordination of N-tosyl formaldimine to InCl2+-DCE, generating an In-complexed iminium intermediate. This then undergoes intermolecular reaction (aza-Prins) with alkene substrate to form a carbocation intermediate, which is chemoselectively attacked by the second N-tosyl formaldimine molecule to form a formaldiminium intermediate. In a final step, this intermediate undergoes the ring closure, leading to hexahydropyrimidine along with the regeneration of catalyst. In addition, our DFT results indicate that N-tosyl formaldimine not only acts as a reactant but also accelerates the 1,3-H-shift as a proton acceptor, giving an experimentally observed allylamide product. Also, the "iminium/alkene/imine" path was supported by calculation results for diastereoselective [2 + 2 + 2] reaction using an internal alkene. Finally, the regioselectivity of the InCl3-catalyzed cycloaddition using allenes along with N-tosyl formaldimine was also analyzed.

Synthesis, DFT and kinetic studies of chromic S-methyldithizone

Dithizone is one of the most well-known trace-metal analysis reagents, however, its S-alkylated derivatives received very little attention up to date. Synthesis, kinetic studies of its photo- and chronochromic reactions, as well as DFT and TDDFT results are presented here. For comparitive purposes the corresponding phenylmercury complex was also synthesized and included in this study. Blue-shifts in λmax of the S-methylated compounds are in excess of 60 nm as compared to the metal complex. Relative geometry optimized energies, atomic charge distribution in conjunction with 1H NMR, as well as TDDFTs all point to the pink syn geometry of S-methyldithizone as the prevalent isomer, with the yellow anti geometry only of slightly higher (3.8 kJ/mol) energy. B3LYP provides significantly better UV–visible spectrum approximation than LC-BLYP, OLYP and PW91. At 20 °C the rate of the chronochromic reaction is 0.0073 s−1 in chloroform, and that of the photochromic return reaction is 0.0023 s−1 in ethanol.

Tunable Electronic, Optical, and Thermal Properties of two- dimensional Germanene via an external electric field

In this paper, we present a tight-binding model based on DFT calculations for investigation the electronic and optical properties of monolayer Germanene. The thermal properties are investigated using Green function method. The required tight binding parameters including the onsite energies and third nearest neighbors hopping and overlap integrals are obtained based on our DFT calculations. Germanene is a semiconductor with zero band gap and linear band dispersion around the K point. The band gap opening occurs in the presence of bias voltage. The band gap is increased linearly with increase of the bias voltage strength. The tight binding results for position of the two first peaks in the optical Infrared region is same with the DFT results. By applying and increasing bias voltage, the dielectric function shows the blue shift by reduction the peak intensity in the energy range E < 1 eV. The thermal conductivity and heat capacity increase with increasing the temperature due to the increasing of thermal energy of charge carriers and excitation them to the conduction bands. The thermal properties of Germanene in the absence of bias U = 0 is larger than that U ≠ 0 and they decrease by further bias strength increasing, due to the increasing band gap with bias.

Chloroform Hydrodechlorination on Palladium Surfaces: A Comparative DFT Study on Pd(111), Pd(100), and Pd(211)

Palladium has been shown to be an effective catalyst for chloroform hydrodechlorination, which serves as a promising treatment method for industrial chloroform waste. To investigate the structure sensitivity of this chemistry on Pd surfaces, we performed a density functional theory (DFT, GGA-PW91) study of the chloroform hydrodechlorination reaction on three distinct facets: Pd(111), Pd(100), and Pd(211). Based on the DFT results, the binding strengths of most surface intermediates generally increase in the following order: Pd(111) < Pd(100) < Pd(211). On all three Pd facets, methane is formed as the preferred reaction product through a pathway in which CHCl3* is fully dechlorinated to CH* first, and then hydrogenated to CH4. We constructed potential energy diagrams (PED) and compared the reaction energetics for chloroform hydrodechlorination on the three Pd facets. We propose that the competition between the desorption of chloroform and its initial dechlorination to form CHCl2* likely determines the hydrodechlorination activity of the catalyst. On Pd(111), the desorption of chloroform is energetically favored over its dechlorination while the dechlorination barriers are lower than the desorption barriers on Pd(100) and Pd(211). On the other hand, Pd(100) and Pd(211) bind atomic chlorine stronger and also catalyze the formation of atomic carbon effectively; both are potential site-blocking species. Our results suggest that the more open facets and step edge sites of a Pd nanoparticle may carry higher intrinsic activity towards chloroform hydrodechlorination than the close-packed facets, yet these under-coordinated sites are more prone to catalyst poisoning.

Mechanistic Insights into Copper-Catalyzed Carboxylations

The copper-NHC-catalyzed carboxylation of organoboranes with CO2 was investigated using computational and experimental methods. The DFT and DLPNO-CCSD(T) results indicate that nonbenzylic substrate...

Synthesis, properties and photovoltaic performance in dye-sensitized solar cells of three meso-diphenylbacteriochlorins bearing a dual-function electron-donor.

Bacteriochlorins are crucial to photosynthesis in bacteria. Studies of air-stable, meso-substituted bacteriochlorins are rare. We herein report the synthesis, properties, and photovoltaic performance of three new air-stable, meso-substituted bacteriochlorins bearing a dioctylfluorenylethyne (denoted as LS-17), a dioctylaminophenylethynylanthrylethyne (LS-43), and a diarylaminoanthrylethyne (LS-45) as the electron-donating groups. Among these LS-bacteriochlorins, LS-17 displays sharp UV-visible absorption bands whereas LS-43 and LS-45 give rise to broadened and red-shifted absorptions. Electrochemical and DFT results suggest that the first oxidation and reduction reactions of these bacteriochlorins are consistent with the formation of the cation and anion radicals, respectively. For dye-sensitized solar cell applications, photovoltaic performance of the LS-45 cell achieves an overall efficiency of 6.04% under one-sun irradiation.

Interphase Boundary Layer-Dominated Strain Mechanisms in Cu &lt;sup&gt;+&lt;/sup&gt; Implanted Zr-Nb Nanoscale Multilayers

Sputter-deposited Zr/Nb nanoscale metallic multilayers with a periodicity of 27 (thin) and 96 nm (thick) were subjected to Cu+ implantation with low and high fluences and then studied using various experimental techniques in combination with DFT calculations. After Cu+ implantation, the thinner multilayer exhibited a tensile strain along c-axis in Nb layers and a compressive strain in Zr layers, while the thicker multilayer showed a compressive strain in both layers. The strain is higher in the thin multilayer and even further pronounced for high fluence. We developed a mathematical method for the fundamental understanding of the deformation mechanisms in metallic multilayers subjected to radiation damage. In the model, the cumulative strain within a layer is described as the combination of two contributions coming from the interfacial region and the inner region of the layers. The semi-analytical model predicts that the interfacial strain is dominant and extends over a certain region around the interface. Predictions are well supported by ab-initio calculations which show that in the vicinity of the interface and in the Zr side, vacancy and interstitials (low energy barriers) exhibit high mobility compared to the Nb side, thus resulting in a high recombination rate. As a consequence, less strain occurs in the Zr side of the interface compared to the Nb side. The density and distribution of various types of defects along the ion profile (low and high damaged regions) are obtained by combining DFT results and the predictions of the model.

Exploring novel biomedical applications of rocksalt CdS system with various Eu concentrations (A theoretical study)

Current research is a computational study in which we focus on calculating optical properties of Eu-doped Cadmium Sulfide (CdS) system. We employ Perdew–Burke–Ernzerhof (PBE)–generalized gradient approximation (GGA) for accomplishment of our study and we assume various Eu concentrations (3.12%, 6.25% and 9.37%) for doping into host CdS lattice. We substitute Cd atoms with Eu atoms while supercell size is kept fixed ([Formula: see text]. We present a detailed comparison among optical properties of pure CdS and various Eu concentrations. Partial density of states (PDOS) plots reveal hybridization among Cd [Formula: see text]-states, S [Formula: see text]-states and Eu [Formula: see text]-states and because of it, material (CdS:Eu) shows exceptional energy transfer which influences optical spectra and electronic properties. A considerable change in absorption spectra is noted, where in comparison to pure CdS, absorption shows blueshift with increasing Eu concentrations. Our DFT results were found to have great resemblance with existing literature. Addition of Eu into the CdS lattice originates novelty in CdS:Eu system and number of potential applications related to the field of biomedical physics, amperometric biosensors, quantum dots (QDs) sensors, photonics, bioprinting, biosensing luminophores, solar cells and optoelectronics industry may be explored in technological perspectives.

Modelling of the Elementary Steps Involved in the Aluminum Electrochemical Deposition from Ionic Liquid Based Solution: The BMImCl/AlCl3 System

The energy hierarchy, of the main chemical species involved in the reaction mechanism relevant to the electrodeposition of aluminum in 1-Butyl-3-methylimidazolium chloride/aluminum trichloride solution (BMImCl/AlCl3), is studied by using ab-initio based theoretical calculations. Eventually, a reasonable theoretical estimate of energies, involved in the principal reactions ruling the aluminum electrodeposition from BMImCl ionic liquid solutions, is obtained. For screening purposes (geometry optimization and Hessian calculations) the CAMB3LYP density functional, DFT, has been used. Then single point (exploiting CAMB3LYP optimized geometries) energy data are obtained at the Møller-Plesset (MP2) level of the theory. They are used to cross-check DFT results. A reaction mechanism emerges in which, although the species AlCl−4 is formed with very high efficiency from the neutral species AlCl3, the competing reaction points to an almost complete conversion of aluminum to the dimeric form into bulk solution. This is observed in the absence and, most importantly, in the presence of a coordinating BMIm+ cation. In this respect, the presence of BMIm+ does not seem to affect significantly the equilibrium between the monomeric and dimeric forms of aluminum. This outcome is very interesting because the dimeric species is directly reduced to yield the metal aluminum. Indeed, a larger concentration of Al2Cl−7 gives due reason for a more effective electrodeposition process, as it is experimentally observed in the ionic liquid medium.

Experimental and ab Initio Studies of Deep-Bulk Traps in Doped Rare-Earth Oxide Thick Films

Lanthanum-doped CeO2 is a promising semiconductor for gas sensing. A combined study applying impedance spectroscopy and first-principle calculations was performed for pure and lanthanum-doped samples. The results showed a strong influence of the localized Ce 4f states on the electrical conduction processes, and an electrical resistance increase, as a function of the exposure to vacuum and air atmospheres. After its modification with a rare-earth element along with exposure to reducing and oxidizing atmospheres, the observed behavior suggested the presence of multi-traps, which depended on the described equilibrium between the oxygen vacancies (Vox ↔ VO. ↔VO..) in a disordered deep-bulk trap location. According to the DFT results, the multi-traps were formed with the creation of an oxygen vacancy far from the doping atom. They were considered to be responsible for the phenomena modifying the Debye-like response. The transfer of electrons from Ce(III) to the adsorbed oxygen species, decreasing the number of...

USING MOLECULAR ELECTROSTATIC POTENTIALS AND FRONTIER ORBITALS FOR THE SURFACE-ENHANCED RAMAN INTERPRETATION OF FLUOXETINE

Raman and surface-enhanced Raman (SERS) spectra of (N-methyl-3-phenyl-3-[4-(trifluoromethyl)phenoxy)propane-1-amine hydrochloride, fluoxetine, have been recorded. Density functional theory with the B3LYP functional was used for optimization of the ground state geometry, calculation of the Raman normal modes of this molecule and the modelling of the SERS effect. Calculated geometrical parameters of fluoxetine fit well with the experimental ones. Based on the recorded data, the DFT results and a normal coordinate analysis based on a scaled quantum mechanical (SQM) force field approach, a complete vibrational assignment of fluoxetine as well as its adsorption behavior on a silver surface (using SERS selection rules) is derived.

Photocatalytic activity of MoS2 nanoparticles: an experimental and DFT analysis

Transition metal dichalcogenide MoS2 nanoparticles have been synthesized by an inexpensive slow evaporation method. The X-ray diffractogram (XRD) showed that the grown particles are in crystalline nature with mixed phase. The calculated average particle size of the prepared nanoparticles is 56 nm. The Fourier transform infra-red (FTIR) and Raman studies confirm the particles are bulk MoS2 in nature. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) images confirm the porosity and the presence of Mo and S elements. Photocatalytic activity of the prepared nanoparticles is tested against methylene blue (MB), and malachite green (MG) dyes and the efficiencies are found to be 93.68% and 85.33%, respectively. The degradation rate constant of MoS2 nanoparticles against MB and MG dyes are 0.0199, 0.01389 min−1, respectively, under visible light for 75 min irradiation. A density functional theory calculation has been performed to validate the photocatalytic experimental results based on bandgap, band edge potentials, and effective mass. The DFT results are related to the experimental values, and the discussions are presented.

Selective removal mechanism of the novel Zr-based metal organic framework adsorbents for gold ions from aqueous solutions

A novel metal organic framework absorbent was synthesized by one step method using 2,2′-dithiodibenzoic acid as organic linker for efficient and selective recovery of Au(III) from aqueous solution. The adsorbent were detected by scanning electron microscope, X-ray diffraction and zeta potential instruments. Its performance was tested by batch experiments. The adsorption isotherm conforms to the Langmuir model, demonstrating that the adsorption process is the uniform monolayer adsorption. The kinetic model is well fitted to the pseudo second-order dynamics model. The maximum adsorption capacity was 1119 mg/g at pH = 2. High temperatures can promote the absorption process. The five adsorption and desorption cycles indicate that the adsorbent has good repeatability for Au(III) adsorption. It could selectively adsorbed Au(III) from wastewater. The adsorption derivefromchelation and reduction. The DFT and XPS results show that Au(III) is mainly adsorbed on the adsorbent by coupling with the S atom. These results indicate that it has a high potential to remove Au(III) from industrial wastewater.