Ab Initio Density Functional Theory Research Articles

Functionalization of low-k surfaces with low-energy Ar ions

In this work low-energy Ar impacts on low- k surfaces were simulated with ab initio density functional theory method. The obtained results reveal the mechanism of CH3-group removal under Ar atom/ion irradiation; the threshold energy of this process was estimated. Keywords: low-k dielectrics, functionalization, simulation, diffusion barriers, methyl groups.

A facile strategy for the growth of high-quality tungsten disulfide crystals mediated by oxygen-deficient oxide precursors.

Chemical vapor deposition (CVD) has been established as a versatile route for the large-scale synthesis of transition metal dichalcogenides, such as tungsten disulfide (WS2). Yet, the precursor composition's role on the CVD process remains largely unknown and remains to be explored. Here, we employ Pulsed Laser Deposition (PLD) in a two-stage approach to tune the oxygen content in the tungsten oxide (WO3-x) precursors and demonstrate the presence of oxygen vacancies in the oxide films leads to a more facile conversion from WO3-x to WS2. Using a joint study based on ab initio density functional theory (DFT) calculations and experimental observations, we unravel that the oxygen vacancies in WO3-x can serve as niches through which sulfur atoms enter the lattice and facilitate an efficient conversion into WS2 crystals. By solely modulating the precursor stoichiometry, the photoluminescence emission of WS2 crystals can be significantly enhanced. Atomic resolution scanning transmission electron microscopy imaging (STEM) reveals that tungsten vacancies are the dominant intrinsic defects in mono- and bilayers WS2. Moreover, bi- and multilayer WS2 crystals derived from oxides with a high V0 content exhibit dominant AA'/AB or AA(A…) stacking orientations. The atomic resolution images reveal local strain buildup in bilayer WS2 due to competing effects of complex grain boundaries. Our study provides means to tune the precursor composition to control the lateral growth of TMDs while revealing insights into the different pathways for forming grain boundaries in bilayer WS2.

Функционализация поверхности low-k диэлектриков ионами Ar низкой энергии

In this work low-energy Ar impacts on low-k surfaces were simulated with ab initio density functional theory method. The obtained results reveal the mechanism of CH3 group removal under Ar atom/ion irradiation; the threshold energy of this process was estimated.

Effect of Gadolinium rare-earth element on Nd2Fe14B permanent magnet

Neodymium-based permanent magnets (Nd2Fe14B) are the potential permanent magnets for use in various applications due to their high magnetic field strength and resistance to demagnetisation. These magnets have various applications in highly efficient energy conversion machines and devices such as wind turbines and electric vehicles due to their exceptional magnetic properties. However, they suffer low operating temperatures below 585 K. In this study, we investigate the effect of Gadolinium (Gd) rare earth element on the Nd2Fe14B magnets. The structural, electronic, mechanical and vibrational properties of the magnets are calculated using the ab initio density functional theory approach. Heats of formation were used to investigate the thermodynamical stability of the magnets, where NdGdFe14B magnets are found to be thermodynamically stable. Moreover, the calculated elastic properties satisfy the tetragonal stability condition which alludes to the stability of NdGdFe14B magnets which is in agreement with the calculated eigenvalues. Furthermore, using the spin-polarized only we calculated the total magnetic moment of the NdGdFe14B magnet (59.92 μb), which is larger compared to that of Nd2Fe14B magnets. Partial substitution of Nd with Gd improves the stability and the magnetic properties of Nd2Fe14B permanent magnets.

Rashba-type spin splitting and transport properties of novel Janus XWGeN2 (X = O, S, Se, Te) monolayers.

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN2 (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN2 are predicted to be stable and they are all indirect semiconductors in the ground state. When the spin-orbit coupling (SOC) is included, a large spin splitting at the K point is found in XWGeN2 monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN2, SeWGeN2, and TeWGeN2. The Rashba parameters in these structures are directionally isotropic along the high-symmetry directions Γ-K and Γ-M and the Rashba constant αR increases as the X element moves from S to Te. TeWGeN2 has the largest Rashba energy up to 37.4 meV (36.6 meV) in the Γ-K (Γ-M) direction. Via the deformation potential method, we calculate the carrier mobility of all four XWGeN2 monolayers. It is found that the electron mobilities of OWGeN2 and SWGeN2 monolayers exceed 200 cm2 V-1 s-1, which are suitable for applications in nanoelectronic devices.

Generation of singlet oxygen catalyzed by the room-temperature-stable anthraquinone anion radical.

The chemical nature and the catalytic selectivity of the complex of anthraquinone and potassium tert-butoxide, AQ-KOtBu, in generating singlet oxygen (1O2) have been studied using a high-level ab initio method and density functional theory (DFT). The results suggest that the stable catalytic center of the AQ anion radical (semiquinone, [AQ˙]-) can be produced at room temperature, which is due to the strong delocalization characteristics of electrons in potassium atoms. Two experimentally observed complexes, the ground state AQ-KOtBu, i.e., C(1), and the photoexcited AQ-KOtBu, i.e., C(2), can be distinguished via the two different electronic states (π-type and σ-type) of the tert-butoxide group. More interestingly, the catalytic selectivity of AQ-KOtBu to generate 1O2 was investigated using multistate density functional theory (MSDFT), and the results suggest that only open-shell 1O2 rather than the closed-shell component can be generated. This work explores the electronic structure and the catalytic nature of AQ-KOtBu, which is of great importance for the application of AQ and its derivatives.

Ab Initio Calculation of Accurate Electronic and Transport Properties of Zinc Blende Gallium Antimonide (zb-GaSb)

This article reports the results of our investigations on electronic and transport properties of zinc blende gallium antimonide (zb-GaSb). Our ab-initio, self-consistent and non-relativistic calculations used a local density approximation potential (LDA) and the linear combination of atomic orbital formalism (LCAO). We have succeeded in performing a generalized minimization of the energy, using the Bagayoko, Zhao and Williams (BZW) method, to reach the ground state of the material while avoiding over-complete basis sets. Consequently, our results have the full physical content of density functional theory (DFT) and agree with available, corresponding experimental data. Using an experimental room temperature lattice constant of 6.09593?, we obtained a direct band gap of 0.751 eV, in good agreement with room temperature measurements. Our results reproduced the experimental locations of the peaks in the total density of valence states as well as the measured electron and hole effective masses. Hence, this work points to the capability of ab-initio DFT calculations to inform and to guide the design and the fabrication of semiconductor based devices—provided a generalized minimization of the energy is performed.

Ab Initio Modeling of the ZnO-Cu(111) Interface

The morphology at the catalytically active interfacial site of ZnO/Cu in the commercial ZnO/Cu/Al2O3 catalyst for CO2 hydrogenation to methanol is still an open question. In the present study, we employ ab initio density functional theory based methods to gain insight into the structure of the ZnO-Cu interface by investigating the morphology of supported ZnO nano-ribbons at the interface with the Cu(111) surface in the presence of hydrogen and water molecules. We find that the stabilities of free-standing ZnO nano-ribbons get enhanced when they are supported on the Cu(111) surface. These supported nano-ribbons are further stabilized by the adsorption of hydrogen atoms on the top of O atoms of the nano-ribbons. Interestingly, the hydrogenated nano-ribbons are found to be equally stable and they appear to be an array of independent chains of ZnOH motifs, suggesting that the hydrogenated nano-ribbons are structurally fluxional. The edge of these fluxional nano-ribbons is stabilized via a triangular reconstruction with a basic composition of Zn6O7H7 in the presence of water molecules. Such a triangular structure gets further stabilized when it is attached to a bulk-like part of the ZnO/Cu(111) system. Furthermore, we find that the triangular reconstruction is energetically favorable even at the methanol synthesis conditions. Therefore, we propose that, under methanol synthesis conditions, the motif Zn6O7H7 represents a stable form at the interface between the bulk-like part of ZnO and the Cu(111) surface in the ZnO/Cu/Al2O3 based commercial catalyst.

YARI-HEUSLER NaYSi BİLEŞİĞİNİN BAZI FİZİKSEL ÖZELLİKLERİ : İLK İLKELER ÇALIŞMASI

The structural, electronic, elastic and optic properties of NaYSi formed in the half-Heusler structure are studied by using ab-initio density-functional theory. The calculated equilibrium lattice constants are compaired with the available experimental and theoretical data. The elastic parameters have calculated. Computed elastic results prove that this compound were mechanically stable. The band gap of this compound predicted to be semiconductor. Further the phonon spectra and optical analysis have been obtained for the energy range of 0–40 eV.

Bandstructure and Size-Scaling Effects in the Performance of Monolayer Black Phosphorus Nanodevices.

Nanodevices based on monolayer black phosphorus or phosphorene are promising for future electron devices in high density integrated circuits. We investigate bandstructure and size-scaling effects in the electronic and transport properties of phosphorene nanoribbons (PNRs) and the performance of ultra-scaled PNR field-effect transistors (FETs) using advanced theoretical and computational approaches. Material and device properties are obtained by non-equilibrium Green’s function (NEGF) formalism combined with a novel tight-binding (TB) model fitted on ab initio density-functional theory (DFT) calculations. We report significant changes in the dispersion, number, and configuration of electronic subbands, density of states, and transmission of PNRs with nanoribbon width (W) downscaling. In addition, the performance of PNR FETs with 15 nm-long channels are self-consistently assessed by exploring the behavior of charge density, quantum capacitance, and average charge velocity in the channel. The dominant consequence of W downscaling is the decrease of charge velocity, which in turn deteriorates the ON-state current in PNR FETs with narrower nanoribbon channels. Nevertheless, we find optimum nanodevices with W > 1.4 nm that meet the requirements set by the semiconductor industry for the “3 nm” technology generation, which illustrates the importance of properly accounting bandstructure effects that occur in sub-5 nm-wide PNRs.

Structural, electronic, elastic, phonon and thermoelectric properties of Heusler-structured intermetallic HfCu2In: Using density functional theory

Structural, electronic, elastic, vibrational and thermoelectric properties of HfCu2In Heusler-structured intermetallic compound in MnCu2Al-type structure with space group Fm-3m has been studied by using ab-initio density functional theory for the first time. The calculated band structure shows the metallic nature of the compound. HfCu2In is ductile which was affirmed by the computed values of the Poisson's ratio, Cauchy's pressure and Pugh's ratio. Thermoelectric properties such as electrical conductivity, Seebeck-coefficient, electronic thermal conductivity and power factor are measured with the BoltzTrap software. The calculated phonon dispersion curve contains positive frequencies in all symmetric directions in the first Brillouin zone, indicating the dynamical stability of the compound in a cubic MnCu2Al-type structure. Furthermore, near the zone center, Raman and infrared phonon modes for alloy have been explored, indicating that the estimated phonon spectra are accurate. The present calculated results are compared with those of the other Heusler alloys of a similar type.

Computational and biological efficacy of stigmasterol against HeLa cells and Vero cells- first time isolated from the ethanolic extract of Annonamuricata Linn leaves

The present study was aimed to analyze the in vitro antioxidant, anti-inflammatory and cytotoxicity activities of isolated bioactive compound stigmasterol (abbreviated as STML) from the leaves of Annonamuricata. Extraction was done using Soxhlet apparatus, TLC, column chromatography and STML in the extracts were identified by Gas-Chromatography and Mass-Spectroscopy (GC–MS) analyses. Characterizations of isolated bioactive compound stigmasterol for purity verified were performed using High-performance liquid chromatography (HPLC) technique. Stigmasterol compound was estimated by DPPH scavenging and ABTS assay, it showed significant values. In vitro cytotoxicity activity of stigmasterol was also tested HeLa cells and Vero cells and IC50 values found that 11.58 µg/ml and 173.8 µg/ml, respectively. The different spectral analysis were also characterized by experimental and well deal with the theoretical ab initio Density functional theory (DFT) method at B3LYP level with 6–311++G(d,p) basis set of provides for the different spectral studies, respectively by using UV-Visible,1Hand 13C nuclear magnetic resonance (NMR) spectroscopy studies. Fourier-transform infrared (FTIR) spectral analysis was carried out. Density Function Theory (DFT) computations enabled us to get different reactive properties of STML. The Rf of STML isolated from the ethanolic extracts of Annonamuricata leaves is 3.707. In conclusion, the results suggest that the investigated compounds are potential drug leads to target HeLa cells and Vero cells.

Unraveling oxidative aging behavior of asphaltenes using ab initio molecular dynamics and static density functional theory

Asphalt aging is a major cause of cracking failure in asphalt pavement. However, owing to the lack of understanding of the asphalt aging mechanism, research on asphalt-targeted antiaging technology has encountered challenges. To address this issue, ab initio molecular dynamics simulations and density functional theory calculations based on the quantum chemistry framework were conducted to explore the reaction pathway and thermodynamic driving force of asphaltene aging. The physical properties of asphaltenes were evaluated to determine the effect of aging on asphaltene performance. The results indicate that asphaltenes undergo aging subreactions at different temperatures, including aromatization of naphthenes, formation of oxygen-containing groups, and homolysis of alkyl side chains. The free energy barriers of these reactions can be ranked in ascending order as aromatization < oxygen-containing group formation < homolysis. The molecular polarity, intermolecular binding energy, and solubility parameter of the asphaltene molecule increased significantly with aging, leading to enhanced agglomeration and reduced compatibility of asphalt components, resulting in the deterioration of asphalt cracking resistance.

The impact of anionic vacancies on the mechanical properties of NbC and NbN: An ab initio study

The development of super-hard materials has recently focused on systems containing heavy transition metal and light non-metallic elements. Niobium carbides and nitrides have previously been identified as potential candidates, however, the volatility of carbon and nitrogen during synthesis make them prone to formation of anionic vacancies, which have the ability of changing the electronic structure, dynamical stability and adversely affecting the mechanical properties. This study presents ab initio Density Functional Theory calculations that probe the occurrence of anionic vacancies as a function of concentration, thereafter, pertinent mechanical properties are investigated. Our results showed that the presence of anionic vacancies in NbC and NbN tend to deteriorate the mechanical properties and ultimately the mechanical hardness due to vacancy softening that can be attributed to defect induced covalent to metallic bond transition. Further, it was observed that anionic vacancies in NbC tend to modify its toughness; in particular, NbC in ZB structure becomes brittle while NbC in WZ phase becomes ductile in presences of C vacancies of up to 6%. The dynamical stability of NbC in RS, ZB, and WZ phases and NbN in WZ phase were found to be insensitive to the presence C and N vacancies, while NbN in RS and ZB becomes dynamically stable with the introduction of N vacancies. In addition, the toughness of NbN was found to be insensitive to defect concentration of even up to 8%. Consequently, stringent control of anionic defects during synthesis of NbC and NbN is critical for realization of the desired mechanical response that can make these materials ideal for super-hard and related applications.

Bulk and surface diffusion of neodymium in alpha-uranium: Ab initio calculations and kinetic Monte Carlo simulations

• A Nd interstitial is found to be intrinsically unstable in alpha- U . • The binding between the substitutional Nd and the U vacancy in strong in alpha- U . • Nd atoms migrate in bulk alpha- U via the vacancy mechanism. • Radiation can significantly accelerate the bulk diffusivity of Nd in alpha- U . • Diffusion of Nd adatoms via pore surfaces is much faster than bulk diffusion. A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and kinetic Monte Carlo (KMC) study of the bulk diffusivity of Nd in α-U , fully taking into account the effect of radiation enhanced diffusion. The vacancy mechanism is considered to be the dominant mechanism for the bulk diffusion of Nd since a Nd interstitial is found to be intrinsically unstable in α-U . The surface diffusivity of a Nd adatom on α-U (001) surface has been further predicted using KMC simulations parameterized by DFT calculations. The present study suggests that Nd transport via the surface diffusion mechanism can be many orders of magnitude faster than bulk diffusion. Furthermore, the results from the present lower length scale study can be used to inform mesoscale phase-field simulations to determine the effective diffusion coefficient of Nd through α-U with a porous microstructure.

Precipitate/matrix incompatibilities related to the {111}Al Ω plates in an Al-Cu-Mg-Ag alloy

The atomic structure of Ω plates forming on {111}Al planes in an Al-Cu-Mg-Ag alloy has been investigated by Z-contrast atomic-resolution scanning transmission electron microscopy imaging and ab initio density functional theory calculations. Ω plates with different thicknesses have been studied in two peak-aged conditions: 150 °C for 24 h and 190 °C for 1.5 h. Volumetric and structural incompatibilities as unrelaxed misfit strains and shear components, respectively, between the Ω plates involving orthorhombic θ-phase fragments and Al matrix were found to be in the plates with thicknesses from 0 to 2.5 cθ (a normal direction to {111}Al). Two types of shear components: [−101]Al // [0−10]θ (τI) and [1−21]Al // [100]θ (τII) related to precipitate/matrix structural incompatibilities have been predicted by calculations. The shear components τI and τII have been found to be energetically favorable in the plates with different thicknesses. Comparing τI and τII absolute values in supercells involving the plates with different thicknesses, 2 cθ thick plates have a shear component close to zero. All the plates analyzed have precipitate/matrix volumetric incompatibilities with Al matrix as misfit strains along [111]Al // [001]θ, which distribute non-uniformly across the plate thickness. Large misfit strains concentrate at the broad plate interfaces, i.e. in Ag2Cu and Cui layers, and cause a prohibitively high barrier to thickening of the Ω precipitates.

Chemical depolymerization of recycled PET to oxadiazole and hydrazone derivatives: Synthesis, characterization, molecular docking and DFT study

The extensive use of polyethylene terephthalate (PET)-based packaging materials has increased the desire to focus on their recycling. In this study, a chemical depolymerization method is proposed for synthesizing terephthalic dihydrazide (TDH) via the aminolysis of post-consumed PET. TDH is further used as a precursor along with 2-chlorobenzoic acid and 4-hydroxybenzoic acid to synthesize aromatic compounds, such as two oxadiazole derivatives, with potential applications. TDH is also used along with 2-chlorobenzaldehyde, benzaldehyde, and 4-hydroxybenzaldehyde to synthesize three hydrazone derivatives. The five compounds (the oxadiazoles and hydrazones) are well characterized by ultraviolet–visible (UV–Vis) spectroscopy, elemental analysis, Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and thermal analysis. The theoretical parameters of the compounds are studied by ab initio density functional theory (DFT). The DFT calculations are conducted at Becke’s three parameter and Lee–Yang–Parr (B3LYP) functional level of calculation with 631-G basis set. Moreover, several thermodynamic parameters at the ground state, such as the point group symmetry, dipole moment, and vibrational frequency, are calculated. The study of molecular docking of the synthesized compounds with target proteins (glucosamine-6-phosphate synthase (GlcN-6-P) and sterol 14α-demethylase (CYP51)) is conducted. Further, different parameters, such as the binding energy (BE), inhibition constant, internal energy, total intermolecular van der Waals forces, unbound energy, and hydrogen bond energy, are calculated. The three of the synthesized compounds are evaluated for antifungal and antibacterial activities using agar well diffusion method. The study of such compounds can offer a good prospective as potential antimicrobial and antifungal leads.

Exciton-polariton properties of hexagonal BN-based microcavity and their potential applications in BEC and superconductivity

Microcavity exciton-polaritons are two-dimensional bosonic quasiparticles composed by excitons and photons. Using a model Hamiltonian with parameters generated from ab initio density-functional theory and Bethe-Salpeter equation calculations, we investigate the exciton and the exciton-polariton properties of hexagnonal boron nitride (hBN) based microcavity. We show that hBN-based microcavities, including monolayer and all-dielectric ones, are promising in optoelectronic applications. Room temperature exciton-polariton Bose-Einstein condensation can be achieved because of the large oscillator strength and binding energy of the exciton, and the strong interaction between the exciton-polaritons and the longitudinal optical phonons. Based on this BEC state, an exciton-polariton mediated superconducting device can also be fabricated at a few tens of kelvin using the microcavity structure proposed by Laussy et al. Phys. Rev. Lett. 104, 106402 (2010).

A Study of Thermoelectric Performance of TlGaSe2 Layered Dichalcogenides from First‐Principles Calculations: Vacancy Defects Modeling and Engineering

Herein, the thermoelectric performance of ternary layered dichalcogenides is evaluated by applying ab initio density functional theory calculations combined with Boltzmann's transport equation. A novel approach to design the intrinsic structural defects via Se‐anion vacancies in unit cell has been developed. Two kinds of ‐vacancy defects in host crystal lattice are engineered: the single vacancy defect induced intrinsically in the unit cell () and in the supercell lattice (). It is found that the electrical transport properties and thermoelectric efficiency of this semiconductor could be significantly altered by introducing Se‐vacancy states into crystalline structure. In addition, simulation shows that inclusion of Se‐vacancy defects significantly improves the thermoelectric efficiency as well as the thermoelectric power factor and figure of merit () values of this compound. Additionally, the thermoelectric performance of is estimated by means of the electronic fitness function calculations in the valence and conduction edges. The results demonstrate that with introduced ‐vacancies may be a perspective material for thermoelectric applications.

Enantioseparation of novel anti-inflammatory chiral sulfoxides with two cellulose dichlorophenylcarbamate-based chiral stationary phases and polar-organic mobile phase(s)

Chiral sulfoxides represent a class of substances of great importance in many fields, including medicinal chemistry dealing with the synthesis of novel cyclooxygenase-2 (COX-2) inhibiting/NO donors. In the present study, two nitrooxyethyl sulfoxides along with their metabolites, hydroxyethyl derivatives have been successfully enantioresolved with two cellulose tris(3,5-dichlorophenylcarbamate)-based chiral stationary phases (CSPs), one with a coated (CSP 1) and the other (CSP 2) with an immobilized chiral selector. The immobilized selector in CSP 2 produced comparable-to-better performances than the coated one in CSP 1 (with α and RS values up to 1.94 and 6.32, respectively) running the analysis with a polar-organic phase made up with an ethanol/2-propanol (80:20, v/v) mobile phase. Electronic circular dichroism studies coupled to ab initio time-dependent density functional theory simulations allowed us to determine the elution order of three out of four compounds. For the two hydroxyethyl derivatives the same enantiomeric elution order [(S)<(R)] was obtained with both CSPs, while the compounds containing the −ONO2 group experienced a different elution order depending on the coated or immobilized nature of the chiral selector [(S)<(R) with CSP 1 and (R)<(S) with CSP 2]. A molecular modeling study based on docking simulations was performed to gain a deeper insight into the enantioseparation mechanism of the hydroxyethyl derivatives on both CSPs.