DFT Data Research Articles

Conducting polymer thin film for optoelectronic devices applications

A crystalline and conjugated semiconductor thin film of poly(o‐phenylene diamine‐co‐m‐phenylene diamine) copolymer [PoPmP]TFwith a thickness of 150 ± 3 nm is fabricated by physical vapor deposition technique (PVD). The copolymer is produced in an acidic solution using oxidative polymerization method. The ratio between the monomers and initiator is 1:1:2. The characterization of the obtained copolymer powder is carried out using different techniques includes Fourier‐transform infrared spectroscopy (FTIR), UV–Vis spectroscopy (UV–Vis), proton nuclear magnetic resonance (1HNMR), X‐ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The structure and optical properties of the thin film were measured experimentally and computationally using DFT simulation. The obtained DFT data provide good proof for the electronic transition in zero‐dimensional [PoPmP] as a single crystal molecule. The obtained thin film presented encouraging outcomes to be a worthy applicant for polymer solar cell uses. This study provides valuable information on the nature and sources of defect formation and electronic transition in conducting doped copolymer which open the way for the application as an optoelectronic device.

How decoration with Tl affects CO electro-oxidation on Pd (1 0 0) nanocubes: In situ FTIR and ab-initio insights

• Pd nanocubes were synthesized, modified by Tl and tested for CO electrooxidation. • Different amounts of Tl influence CO electrooxidation reaction on these surfaces. • CO adsorbs in a two-site geometry on clean Pd surfaces. • The adsorption geometry changes for on-top in presence of minor amounts of Tl. • DFT data reveals that high Tl coverages hinder CO adsorption on Pd. In this work we prepare Pd (1 0 0) preferentially oriented nanoparticles modified with different amounts of Tl and study the CO electro-oxidation reaction on these surfaces in alkaline medium. The analysis is based on cyclic voltammetry coupled with in situ FTIR spectroscopy, and the results are interpreted with the help of a DFT study. In situ FTIR indicates a change in the CO adsorption geometry on Pd surfaces partially covered by Tl, while DFT data reveal that for high Tl coverages CO adsorption is completely inhibited. Based on our findings, by using the proper amount of Tl, one can think in the development of Pd-based catalysts designed to present tolerance to CO poisoning, aiming their application in the electro-oxidation of small organic molecules.

Synthesis, Characterization and Antimicrobial Studies of Some New Tellurium(IV) Complexes Derived from 2-[(2-Hydroxyphenyl)imino methyl]-1-naphthol Schiff Base

This article reports the synthesis, characterization and antimicrobial screening of a tridentate 2-[(2-hydroxyphenyl)imino methyl]-1-naphthol ligand (H2AP) and its organotellurium(IV) complexes. Structural characterization of the synthesized ligand and complexes was confirmed by using FT-IR, 1H NMR, 13C NMR, UV-vis, mass spectrometry, molar conductance and elemental analysis. Geometry of all the synthesized compounds has been optimized and their DFT based chemical reactivity descriptors were calculated. DFT and spectral data studies revealed distorted square pyramidal geometry for the tellurium(IV) complexes. In vitro antimicrobial activities of the synthesized ligand and its tellurium(IV)complexes were evaluated against two Gram-positive, two Gram-negative bacterial strains and three fungal strains. The tellurium(IV) complexes exhibited promising activity as compared to the Schiff base ligand.

π-Extended dibenzo[g,p]chrysenes

Two different series of π-extended dibenzo[g,p]chrysenes are synthesized. The experimental and DFT data showed the significant effects of both position and substituent on the optoelectronic and charge delocalization behavior.

Incomplete cocrystalization of ibuprofen and nicotinamide and its interplay with formation of ibuprofen dimer and/or nicotinamide dimer: A thermodynamic analysis based on DFT data.

Cocrystallization of ibuprofen and nicotinamide in hot melt extrusion process has been subject of many studies addressing low ibuprofen bioavailability. However, it is observed that the process of cocrystal formation of ibuprofen and nicotinamide might be incomplete. We hypothesized that formation of dimers of ibuprofen-ibuprofen or dimers nicotinamide- nicotinamide might be the cause of such poor cocrystalization process by altering the phase behaviour of the mixture. This paper addresses the molecular thermodynamics of mixtures of ibuprofen and nicotinamide, with special focus on the possibility of formation of these dimers and their corresponding interplay with mixture phase behaviour. For this purpose, density functional theory calculations are used to calculate electron donor-acceptor sizes on each molecule and accordingly possible dimers of each molecule are analysed. The free energies and phase diagram are determined for (1) when a dimer is formed or (2) no dimer is formed, over a wide operating temperature range of 273.15K-390K. The binding and solvation energies are calculated to identify/rank dimers. Calculations showed that formation of dimers requires an energy input which can be accessible noting to the external heating in hot melt extrusion process. The calculated solvation energies of the dimers suggest that addition of liquid binder (water) can mitigate the risk of dimer formations. Addition of proper binder/excipient is an easy route to compensate such dimer formation and to engineer ibuprofen and nicotinamide cocrystallization behaviour.

A comprehensive diffusion mobility database comprising 23 elements for magnesium alloys

Reliable experimental diffusion coefficients of 10 key alloying elements in Mg obtained by the present authors together with experimental data in the literature enabled us to perform a systematic test of the reliability of diffusion coefficients obtained from DFT calculations. The computed activation energy values were found to be quite accurate (mostly within 0.2 eV) but the computed pre-factors were less reliable. Such insights allowed us to develop a practical and yet robust strategy to perform diffusion mobility assessments by adopting the computed activation energy while fitting only the pre-factor when available experimental data are limited to a narrow temperature range. The overall good agreement between the DFT data and experimental data also gave us the confidence to employ the computed data for those that were still missing or inaccessible from experimental measurements. A systematic assessment of both the measured and computed diffusion data in hcp Mg was performed using the above holistic approach to yield the most comprehensive open Mg mobility database to date, comprising 23 elements (Mg, Ag, Al, Be, Ca, Cd, Ce, Cu, Fe, Ga, Gd, In, La, Li, Mn, Nd, Ni, Pu, Sb, Sn, U, Y, Zn). This more reliable mobility database will contribute to future development of advanced Mg alloys. The holistic approach developed in this study will be very beneficial to the future establishment of reliable mobility databases for other alloy systems as well.

Quantitative and qualitative performance of density functional theory rationalized by reduced density gradient distributions

We evaluate the qualitative and quantitative accuracy of various flavors of density functionals with and without accounting for dispersion corrections. Our test system is nickel in the form of bulk, surfaces, and nanoparticles for which we compute structural properties, bulk cohesive energies, surface energies, and work functions and compare to experimental data. We find that the inclusion of any dispersion, either by an a posteriori correction or by a self-consistent treatment by explicitly computing the nonlocal correlation contribution to the total energy, has a significant effect on the calculated properties and improves the quantitative comparison to experiments. Besides the quantitative agreement, we also investigate qualitative features by comparing Wulff shapes of metal nanoparticles as obtained using the different density functionals. We find that all tested functionals predict similar Wulff shapes for nickel nanoparticles but still have some small differences. These results show that the relative energies calculated using the semilocal GGA and meta-GGA functionals, with and without dispersion, are quite similar. Our findings can also be generalized to other systems when rationalized in terms of the computed reduced density gradients. We find that the distribution of reduced density gradients in a material is correlated to the steepness of the exchange enhancement factor and propose that this information can be used as a quantitative guide when it comes to picking the most appropriate density functional for specific target systems as well as when it comes to extrapolating DFT data to predict experiments.

Calphad Modeling of LRO and SRO Using ab initio Data

Results from DFT calculations are in many cases equivalent to experimental data. They describe a set of properties of a phase at a well-defined composition and temperature, T, most often at 0 K. In order to be practically useful in materials design, such data must be fitted to a thermodynamic model for the phase to allow interpolations and extrapolations. The intention of this paper is to give a summary of the state of the art by using the Calphad technique to model thermodynamic properties and calculate phase diagrams, including some models that should be avoided. Calphad models can decribe long range ordering (LRO) using sublattices and there are model parameters that can approximate short range ordering (SRO) within the experimental uncertainty. In addition to the DFT data, there is a need for experimental data, in particular, for the phase diagram, to determine the model parameters. Very small differences in Gibbs energy of the phases, far smaller than the uncertainties in the DFT calculations, determine the set of stable phases at varying composition and T. Thus, adjustment of the DFT results is often needed in order to obtain the correct set of stable phases.

Structural, DFT, vibrational spectroscopic, thermal, electrical and magnetic characterizations of hydrothermally grown CoCO3 microcrystals

The minerals such as the CoCO3 can be utilized for the fabrication of lithium-grafted batteries and for a variety of food applications. In this study, we have successfully synthesized Cobalt carbonate crystals (CoCO3) using hydrothermal synthesis method. The synthesized micro-crystals consist of hexagonal structure symmetry. The XRD shows the single-phase hexagonal (R-3c) crystal with lattice constants a = 4.661 A, b = 4.661 A, and c = 14.96 A. EDAX spectroscopy analysis confirms the presence of all the elements of sample. FE-SEM analysis suggests nearly rod-shaped crystals with ~ 29 µm average crystalline size. The Fourier Transform Infrared spectrum suggested existence of O–H, C–O etc. bonding. The TGA is carried out to study the thermal stability. The dielectric relaxation is well studied over large angular frequency range. Complex impedance spectrum of the synthesized microcrystals consists of single semi-circular arc due to the presence of grain only. The magnetic study has suggested paramagnetic nature of the sample. The theoretical study such as the density function theory has been carried out using the Quantum ESPRESSO. A reasonably good agreement is observed between experimentally obtained data and DFT data for optimized structures.

Angular dependent interatomic potential for Ti-V system for molecular dynamics simulations

Abstract An interatomic potential for the Ti-V binary alloy focusing on evolution of defects, including ones arising as a result of the irradiation process, was constructed within the Lipnitskii-Saveliev approach, which accurately takes into account three-particle interactions and the sum of all multi-particle interactions of a higher order in the framework of the centrally symmetric approximation. In the new potential, Ti-V interactions were fitted to the DFT data on set of model structures with different coordination numbers, including ones with vacancies. The properties used for fitting are accurately reproduced by the present potentials for both pure elements and alloy systems. The potential was tested on the binding energies between Ti atoms and self-point defects in bcc V, elastic moduli, thermal expansion and melting point of some alloys, and diffusion. We obtained qualitative agreement for these properties with available theoretical and experimental data. Finally, we investigated evolution of excess vacancies in the V-4 at. \% Ti alloy at 700 K, which are typical conditions of vanadium-based alloys for fusion applications. We found that no vacancy loop is formed in the alloy in contrast to the pure V, which agrees with the experimental observations. The potential is expected to be especially suitable for irradiation simulations of vanadium based V-Ti alloys.

Synthesis, photophysical properties, and density functional theory studies of phenothiazine festooned vinylcyclohexenyl-malononitrile.

A novel phenothiazine derivative conjugated with vinylcyclohexenyl-malononitrile (PTZ-CDN) was synthesized through the Knoevenagel reaction of 10-octyl-10H-phenothiazine-3,7-dicarbaldehyde with 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)-malononitrile and fully characterized. The UV-vis absorption spectra of PTZ-CDN in different solvents showed a λmax band at 497-531 nm with a high molar extinction coefficient attributed to intramolecular charge transfer (ICT) with the characteristics of a π-π* transition. Increasing the solvent polarity resulted in a bathochromic shift of λmax . The PTZ-CDN fluorescence emission spectra were more sensitive to increasing the solvent polarity than the absorption spectra; they displayed a blue shift of λem by 85 nm. To understand the behaviour of the PTZ-CDN derivative, Stokes' shift ( with respect to the solvent polarity, Lippert-Mataga and linear solvation-energy relationship (LSER) models were applied in which the LSER showed better regression than the Lippert-Mataga plots (r2 = 0.9627). Finally, the TD-density functional theory (DFT) electronic transition spectra in dioxane and dimethyl formamide (DMF) were calculated. The DFT data showed that λmax resulted from the support of the highest occupied molecular orbital to the lowest unoccupied molecular orbital transition with 74% and 99% in dioxane and DMF, respectively.

Catalytic Activity of trans-Bis(pyridine)gold Complexes.

Gold catalysis has become one of the fastest growing fields in chemistry, providing new organic transformations and offering excellent chemoselectivities under mild reaction conditions. Methodological developments have been driven by wide applicability in the synthesis of complex structures, whereas the mechanistic understanding of Au(III)-mediated processes remains scanty and have become the Achilles’ heel of methodology development. Herein, the systematic investigation of the reactivity of bis(pyridine)-ligated Au(III) complexes is presented, based on NMR spectroscopic, X-ray crystallographic, and DFT data. The electron density of pyridines modulates the catalytic activity of Au(III) complexes in propargyl ester cyclopropanation of styrene. To avoid strain induced by a ligand with a nonoptimal nitrogen–nitrogen distance, bidentate bis(pyridine)–Au(III) complexes convert into dimers. For the first time, bis(pyridine)Au(I) complexes are shown to be catalytically active, with their reactivity being modulated by strain.

Thermodynamic modeling of G-phase and assessment of phase stabilities in reactor pressure vessel steels and cast duplex stainless steels

Thermodynamic modeling of G-phase in iron-based multicomponent systems was revised and updated by means of a careful literature survey. The thermodynamic parameters were optimized based on DFT data. Additionally intermetallic phases with possible competition to G-phase in multicomponent systems were also optimized. The thermodynamic model parameters were added to multicomponent thermodynamic database and used for calculation of technological steels and possible competition between phases are tested and shown.

New complexes of usnate with lanthanides ions: La(III), Nd(III), Tb(III), Gd(III), synthesis, characterization, and investigation of cytotoxic properties in MCF-7 cells

New lanthanides ions complexes were synthesized from the reactions of aqueous – ethanolic solution of the sodium usnate with an aqueous solution of the lanthanides ions. DFT data, UV–VIS spectroscopy, IR, 1H NMR, 13C NMR, HMBC, and elemental and thermal analyses, are consistent with the following general coordination formula: [LnL3(H2O)x], wherein L = C18H15O7–, Ln = Gd(III), Tb(III), x = 2 and Ln = La(III), Nd(III), x = 3. The chelates presented higher cytotoxic activity in breast cancer tumor cells (MCF-7) compared to organic and inorganic precursors. The two more potent compounds, complexes of La(III) and Gd(III), were tested in non-tumorigenic breast cells MCF-10A, showing less cytotoxicity, which evidenced their selectivity towards tumor cells.

Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

We report on the impact of magnetoelastic coupling on the magnetocaloric properties of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ in terms of the vibrational density of states, which we determined with $^{57}$Fe nuclear resonant inelastic X-ray scattering measurements and with density-functional-theory based first-principles calculations in the ferromagnetic low-temperature and paramagnetic high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between non-hydrogenated and hydrogenated samples. This shows that hydrogen does not only shift the temperature of the first-order phase transition, but also affects the elastic response of the Fe-subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. As a consequence, the change in the Fe specific vibrational entropy $\Delta S_\mathrm{lat}$ across the phase transition has the same sign as the magnetic and electronic contribution. DFT calculations show that the same mechanism, which is a consequence of the itinerant electron metamagnetism associated with the Fe subsystem, is effective in both the hydrogenated and he hydrogen-free compounds. Although reduced by 50 % as compared to the hydrogen-free system, the measured change $\Delta S_\mathrm{lat}$ of 3.2\pm1.9 J/kgK across the FM to PM transition contributes with 35 % significantly and cooperatively to the total isothermal entropy change $\Delta S_\mathrm{iso}$. Hydrogenation is observed to induce an overall blueshift of the Fe-VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ was determined from the NRIXS and the DFT data.

Ab initio calculations of nuclear quadrupole resonance frequencies in trichloroacetyl halides: a comparison of DFT and experimental data

Ab initio calculations of 35Cl nuclear quadrupole resonance (NQR) frequencies (νQ) in trichloroacetyl halides (CCl3COHal, where Hal = F, Cl, Br or I) are performed. The estimated νQ values are compared with experimental values obtained by Gordeev et al []. Calculation of the average of 35 Cl NQR frequencies in CCl3COCl demonstrated that the difference between the calculated and experimental values are less than 3.1%. This indicates that the density functional theory is a powerful technique that for predicting unknown electronic states before performing experiments. A linear correlation between Hal-C bond length and νQ is observed. This hence provides a scheme to estimate interatomic distances using NQR frequencies.

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.

Importance of the fourth-rank zero field splitting parameters for Fe2+ (S = 2) adatoms on the CuN/Cu(100) surface evidenced by their determination based on DFT and experimental data.

Due to their potential applications, single atoms on surfaces (adatoms) have been extensively studied using STM, IETS, INS, and EPR techniques or using DFT and ab initio methods. Especially interesting are Fe2+ (S = 2) adatoms on CuN/Cu(100) and Cu2N/Cu(100) surfaces due to their non-Kramers features described by the zero field splitting (ZFS) Hamiltonian. The 4th-rank ZFS parameters (ZFSPs), allowed for spin S = 2, are commonly disregarded. By extracting 4th-rank ZFSPs from DFT predicted spin energy levels for the Fe2+@CuN/Cu(100) system, we show that including only 2nd-rank ZFSPs yield incomplete description of magnetic and spectroscopic properties. The algebraic method developed by us is used to extract 2nd- and 4th-rank ZFSPs utilizing knowledge of energy levels without a magnetic field, which may be obtained experimentally or theoretically. Reasonable constraints on particular 4th-rank ZFSPs are considered based on comparison of data on ZFSPs and energies for Fe2+@CuN/Cu(100) and other Fe2+ (S = 2) systems. Influence on energies due to 2nd-rank ZFSPs alone versus that of both 2nd- and 4th-rank ZFSPs is analyzed. A series of simulations of ZFS energies for different ZFSP variants is carried out. The results prove the importance of 4th-rank ZFS parameters. Our method enables a more accurate description of 3d4 and 3d6 (S = 2) ions in various systems, including S = 2 adatoms.

Angular ladder-type meta-phenylenes: synthesis and electronic structural analysis.

Herein, we report the synthesis of two new series of angular (all-syn) ladder-type meta-[n]phenylenes (LMP, n = 3-8). One series contains keto groups at the termini bridges, denoted angular keto (AKn), the second contains alkyl groups at all bridge sp3 carbons, denoted angular alkyl (AAn). Their electronic and structural properties were delineated by a combination of electrochemistry and spectroscopic (UV-Vis and emission) methods and further supported by DFT calculations. Interestingly, experimental and DFT data show that changing the bridging group at the termini from alkyl (AAn) to keto (AKn) gives an increase in the first reduction potentials and LUMO energies, as the π-system is extended. Also, the charge (de)localization behavior is different for these two species; while the AAn compounds stablize charge with Robin-Day class III, the AKn compounds show a clear switch from class III to class II. In comparison with the linear analogues (LKn and LAn), DFT results reveal a shape independency of the charge (de)localization mechanism in acceptor-π-acceptor series (AKn/LKn).

Electrochemical Synthesis of Hindered Primary and Secondary Amines via Proton-Coupled Electron Transfer.

Accessing hindered amines, particularly primary amines α to a fully substituted carbon center, is synthetically challenging. We report an electrochemical method to access such hindered amines starting from benchtop-stable iminium salts and cyanoheteroarenes. A wide variety of substituted heterocycles (pyridine, pyrimidine, pyrazine, purine, azaindole) can be utilized in the cross-coupling reaction, including those substituted with a halide, trifluoromethyl, ester, amide, or ether group, a heterocycle, or an unprotected alcohol or alkyne. Mechanistic insight based on DFT data, as well as cyclic voltammetry and NMR spectroscopy, suggests that a proton-coupled electron-transfer mechanism is operational as part of a hetero-biradical cross-coupling of α-amino radicals and radicals derived from cyanoheteroarenes.