Density Functional Study Research Articles

Pyrolysis mechanism study of n-heptane as an endothermic hydrocarbon fuel: A reactive molecular dynamic simulation and density functional theory calculation study

The pyrolysis of endothermic hydrocarbon fuel with high heat sink can reduce the surface temperature of engines and aircraft fuselage. The pyrolysis mechanism of n-heptane as a model compound for endothermic hydrocarbon fuel was investigated by using ReaxFF reactive molecular dynamic simulations and density functional theory calculations. The results showed that the breakage of CC bonds of n-heptane were easier than that of CH bonds, in which the cleavage of C2C3 bond is the easiest to generate C2H5 and C5H11 radicals. Temperature has a significant effect on the pyrolysis process of n-heptane, and the increase of temperature will accelerate the pyrolysis of n-heptane and promote the formation of pyrolysis products. The pre-exponential factor and apparent activation energy of the n-heptane pyrolysis were 5.4456 × 1014 s−1 and 231.3 kJ·mol−1, respectively.

Relevance of implicit and explicit solvent in density-functional theory study of adsorption at electrochemical NaCl/Al interface

The adsorption behavior of NaCl on Al(111) surface was studied by density functional theory (DFT) using implicit or explicit solvation models. Charge and total energy of adsorption systems indicate that the inclusion of an implicit solvent is necessary to construct a situation relevant to corrosion. Only certain configurations containing explicit water molecules with a direct NaCl interaction with Al are relevant to corrosion scenarios, attributed to a more predominant interaction of H2O-Al over NaCl-Al. Implicit and explicit solvent models yield consistent results, confirming that both solvent models can be used to study Cl- adsorption on Al within a corrosion regime.

A combined helium atom scattering and density-functional theory study of the Nb(100) surface oxide reconstruction: Phonon band structures and vibrational dynamics

Helium atom scattering and density-functional theory (DFT) are used to characterize the phonon band structure of the (3 × 1)-O surface reconstruction of Nb(100). Innovative DFT calculations comparing surface phonons of bare Nb(100) to those of the oxide surface show increased resonances for the oxide, especially at higher energies. Calculated dispersion curves align well with experimental results and yield atomic displacements to characterize polarizations. Inelastic helium time-of-flight measurements show phonons with mixed longitudinal and shear-vertical displacements along both the ⟨1̄00⟩, Γ̄X̄ and ⟨11̄0⟩, Γ̄M̄ symmetry axes over the entire first surface Brillouin zone. Force constants calculated for bulk Nb, Nb(100), and the (3 × 1)-O Nb(100) reconstruction indicate much stronger responses from the oxide surface, particularly for the top few layers of niobium and oxygen atoms. Many of the strengthened bonds at the surface create the characteristic ladder structure, which passivates and stabilizes the surface. These results represent, to our knowledge, the first phonon dispersion data for the oxide surface and the first ab initio calculation of the oxide's surface phonons. This study supplies critical information for the further development of advanced materials for superconducting radiofrequency cavities.

Structure, mechanical and thermo-physical properties of lanthanide fission product doped UO2 in U(V) state: A density functional study

During the nuclear fission of UO2 fuel, many fission products are generated which are trapped in the fuel matrix. These fission products can amend the mechanical and thermo-physical properties of UO2 fuel, which are a prime concern for nuclear safety. In this regard, we investigate the effect of different lanthanide (Ln) fission products on structural, mechanical, electronic and thermal properties of UO2. The substitution of U4+ ions by Ln3+ ions creates a charge imbalance in the lattice which will be neutralized by either oxidation of U atoms from +4 to +5 state (U2Ln2O8) or creation of oxygen vacancies (U2Ln2O7). Here, we study the former case, where the U(IV) ions are oxidized to U(V) state in the Ln substituted UO2 (Ln- UO2) fuel using density functional theory with Hubbard-U corrections. The volume of different Ln-UO2 structures is calculated and compared with undoped UO2. The mechanical properties such as bulk modulus and Young's modulus are calculated from the optimized structures of Ln-doped UO2 and show deviation from undoped UO2 and Ln-doped UO2 with oxygen vacancies. The total density of states and projected density of states indicate that the presence of Ln fission products alters the electronic properties of UO2. The thermal property such as specific heat capacity is evaluated at different temperatures using quasi-harmonic approximation applied to phonon frequencies obtained from density functional perturbation theory. We do observe an excellent agreement of the calculated specific heat capacity with the experimental values for the pure UO2. The counter balancing effect of heat capacity values of U2Ln2O8 and U2Ln2O7 systems may control the net heat capacity of the UO2 fuel matrix.

Hydrogen-Bond-Assisted Diels-Alder Kinetics or Self-Healing in Reversible Polymer Networks? A Combined Experimental and Theoretical Study.

Diels–Alder (DA) cycloadditions in reversible polymer networks are important for designing sustainable materials with self-healing properties. In this study, the DA kinetics of hydroxyl-substituted bis- and tetrafunctional furans with bis- and tris-functional maleimides, both containing ether-functionalized spacers, is investigated by modelling two equilibria representing the endo and exo cycloadduct formation. Concretely, the potential catalysis of the DA reaction through hydrogen bonding between hydroxyl of the furans and carbonyl of the maleimides or ether of the spacers is experimentally and theoretically scrutinized. Initial reaction rates and forward DA rate constants are determined by microcalorimetry at 20 °C for a model series of reversible networks, extended with (i) a hydroxyl-free network and hydroxyl-free linear or branched systems, and (ii) polypropylene glycol additives, increasing the hydroxyl concentration. A computational density-functional theory study is carried out on the endo and exo cycloadditions of furan and maleimide derivatives, representative for the experimental ones, in the absence and presence of ethylene glycol as additive. Additionally, an ester-substituted furan was investigated as a hydroxyl-free system for comparison. Experiment and theory indicate that the catalytic effect of H-bonding is absent or very limited. While increased concentration of H-bonding could in theory catalyze the DA reaction, the experimental results rule out this supposition.

“Upper” Ring Expansion of the Planar Blatter Radical via Photocyclization: Limitations and Impact on the Electronic Structure

Photocyclization of 8-aryloxybenzo[e][1,2,4]triazines leads to the formation of π-expanded flat Blatter radicals for three phenanthryloxy and pyren-1-yloxy derivatives, whereas no photoreaction is observed for the perylen-3-yloxy precursor. Two of the new radicals are nonplanar, out of which one is unstable to isolation. The radical with the fused pyrene ring constitutes the largest thus far paramagnetic polycyclic π-system containing seven fused rings with 27 sp2-hybridized atoms and 29 π-delocalized electrons. The investigation of the reaction conditions demonstrated the higher efficiency of photoformation of the parent radical in polar solvents, which suggests a polar transition state and the S1 photoreactive state. The effect of π expansion on the electronic structure was investigated with spectroscopic (UV-vis, electron paramagnetic resonance) and electrochemical methods augmented with density functional theory computational studies. The molecular structure of one of the radicals was determined with a single-crystal X-ray diffraction method.

Density functional study of Ga intercalation at graphene/SiC heterointerface

Density functional study of Ga intercalation at graphene/SiC heterointerface

Noncovalent Interaction- and Steric Effect-Controlled Regiodivergent Selectivity in Dimeric Manganese-Catalyzed Hydroarylation of Internal Alkynes: A Computational Study.

Selective hydroarylation of internal alkynes catalyzed by a dimeric manganese complex provides a powerful strategy for the construction of multisubstituted alkenes. In this work, density functional theory (DFT) calculations and experimental studies were carried out to explore the mechanism and origin of regiodivergent hydroarylation of internal alkynes reported by our group. The results demonstrate that this reaction first proceeds via a bimetallic mechanism to generate the active catalyst that subsequently undergoes a monometallic mechanism to run the three-stage catalytic cycle: alkyne migratory insertion, protonation, and active catalyst regeneration. Alkyne migratory insertion is considered as the regioselectivity-determining step. Energy decomposition analyses on insertion transition states suggest that the interaction between the substrate and catalyst is mainly responsible for the observed exclusive γ-selectivity of 1a, while the deformation of these two sections induced by the sterically hindered phenyl group and aryl group accounts for the complete β-position arylation of 1e. The decrease of γ-selectivity with the regulation of a tertiary alcohol motif in 1a originates from the reduced noncovalent interaction. The computational results provide important insights into the origin of regiodivergent selectivities and useful information for further designing and adjusting the strategy in Mn-catalyzed alkyne hydroarylation.

Hollow structures of TinOm systems with m ≈ 2n: A density functional theoretical study

We performed density-functional-theoretical calculations of almost stoichiometric structures of hollow cages of TinOm systems with m ≈ 2n. We study the stability of TinOm hollow particles of different sizes and shapes for systems between 80 and 110 atoms using the binding energy as stability criterion. These cages could be useful in electrochemiluminescenece sensors, energy systems, encapsulation of beauty ingredients, and even in biomedical applications. Our results suggest the possible existence of such structures in a great variety of geometrical shapes with small binding energy differences among them, thus presenting a very dense spectrum of possible metastable configurations. Different initial seeds converge to the same final structures, which is also a signature for stability. These results are along the line of experiments in larger size systems, which demonstrate the feasibility of these structures without apparent size limitations.

Optoelectronic properties of Ag2S/graphene and FeS2/graphene nanostructures and interfaces: A density functional study including dispersion forces

The optoelectronic properties of several Ag2S/graphene and FeS2/graphene nanostructures are examined through density functional theory calculations including dispersion forces. First, we analyzed the electronic structure of Ag2S and FeS2 nanocluster models, as prototypes of quantum dots, focusing on the electronic structure and absorption spectra. In the case of FeS2 nanoparticle, both ferro- and antiferromagnetic arrangements were considered. Then, Ag2S and FeS2 nanoclusters were adsorbed on top of both graphite and graphene slab models to study the stability of the systems as well as the effect of the nanocluster–surface interaction in the electronic structure, including an insight into the electron injection mechanisms in these systems. Finally, interface models, consisting of Ag2S or FeS2 thin films adsorbed on a graphene layer, were built and their optoelectronic properties examined. Overall, the results obtained in this work, support the suitability of these systems for their usage in solar cells.Graphical abstract

Methanol-induced luminescence vapochromism based on a Sb3+-doped organic indium halide hybrid

Ion doping has been demonstrated as a practical approach to achieving highly efficient luminescence in both inorganic phosphors and organic-inorganic hybrids. The as-formed doping species show great potential in optoelectronic applications due to their high photoluminescence quantum yield (PLQY) and excellent stability. Herein, we report highly emissive Sb3+-doped indium halides (C6H18N2)InCl5·H2O:Sb (C6H18N22+ = N,N,N′,N′-tetramethylethane-1,2-diammonium) prepared by solution evaporation methods with an emission that peaked at 565 nm and a PLQY of 74.6%. Photophysical characterizations and density functional theory computational studies verify the broadband emission originating from a self-trapped exciton. Interestingly, a drastic red shift of the emission peak from 565 to 663 nm with yellow luminescence turning to red is observed once the (C6H18N2)InCl5·H2O:Sb hybrid is exposed to methanol vapor. Moreover, when the methanol-exposed hybrid is put in air, the emission reverts to 565 nm in several minutes. Single-crystal X-ray diffraction studies show a subsequent structure distortion upon the coordination of methanol to the Sb(III) center, which is responsible for the drastic red shift of the emission. Encouragingly, we found that (C6H18N2)InCl5·H2O:Sb exhibits a specific response to methanol vapor after screening a series of volatile organic compounds with different polarities. Besides, a negligible change of the emission intensity is observed after several cycles of uptaking and releasing methanol. The high fatigue resistance and specific solvent response of the Sb3+-doped indium halide make it a very promising methanol detector.

Defluorination mechanism related to the activity of hydroxyl groups: A combined density functional theory calculations and experimental study

Aluminum-based (Al-based) materials are of great significance to solve the global fluoride pollution problem. Hydroxylation modification is one of the effective methods to improve the surface activity and defluorination performance of aluminum matrix materials. However, the lack of in-depth understanding of the role of hydroxyl gourp at the molecular level restricts the preparation and application of Al-based adsorbents. In this work, based on the interface of Al-based two-dimensional materials, the effects of anionic ligands, doped metals and solution H+ on the structural activity of surface hydroxyl groups were explored by DFT theoretical calculation and experimental design. Simultaneously, quantitative analysis of the contribution of each possible mechanism in the defluorination process was carried out. Both anionic exchange reaction and chemical co-adsorption determined the defluorination process. The high polarizability and more negative charge of anionic ligands was found to facilitate reducing the activity of hydroxyl groups in weak acid environment. H+ can enhance the activity of hydroxyl, and thereby strengthening the hydrogen bond (H-bond) effect, but it will have a synergistic effect with anionic ligands. Metal doping will change the electron density on O atoms, which will affect the F- adsorption effect of hydroxyl via H-bond. Compared with the existing research, we carefully studied the influence of hydroxyl group activity on the defluorination performance of aluminum matrix materials, which can provide a feasible basis for structural design of the subsequent adsorbents.

A density functional study of the structural, electronic, optical and lattice dynamical properties of AgGaS2

Based on first-principles density functional theory the electronic structure, optical and lattice dynamical properties of infrared nonlinear optical crystal AgGaS2 (AGS) are calculated with four different hybrid functional (PBE0, HSE03, HSE06, B3LYP) respectively. The results show that the theoretical results obtained by PBE0 method are in good agreement with the experimental values. The geometrical structure optimization results show that the theoretical lattice parameters of AGS are in good agreement with the experimental values. The electronic structure results show that AGS is a direct wide band gap nonlinear optical crystal, and the band gap obtained by PBE0 method is 2.66 eV, which is basically in good agreement with the experimental values. The calculation results of energy band structure and density of states show that the value band edge is mainly contributed by S-3p, Ag-4d and a small amount of Ga-4p orbital electrons, while the bottom of conduction band is mainly contributed by Ag-5 s, Ga-4 s, 4p and a small amount of S-3p orbital electrons. The orbital coupling between Ga and S atoms determines the optical properties of AGS. Ag atoms contribute little to the optical properties. Especially, the results show that the crystal material has strong absorption and reflection characteristics in the ultraviolet region and strong transmittance in the infrared region. The average static dielectric constant and average static refractive index are 1.887 and 2.14, respectively, and the static birefringence is 0.02.Based on the density functional theory of linear response, the phonon dispersion curve of AGS is calculated. The results show that AGS has no virtual frequency and its dynamic performance is relatively stable. Meanwhile, the optical mode frequency of the Γpoint in the center of Brillouin region is analyzed in detail. The above results show that AGS crystal material enjoys large nonlinear optical coefficient and suitable birefringence in a wide infrared band, and AGS is an important infrared nonlinear optical crystal material.

Density functional methods study on the structures and spectral characteristics for pharmacophoric conformers, metabolites, and combined fragments of Erlotinib

Density functional methods study on the structures and spectral characteristics for pharmacophoric conformers, metabolites, and combined fragments of Erlotinib

Ab initio mechanistic insights into the stability, diffusion and storage capacity of sI clathrate hydrate containing hydrogen

Gas hydrates are non-conventional materials offering great potential in capturing, storage, and sequestration of different gases. The weak van der Waals interactions between a gas molecule and the pore walls stabilize these non-stoichiometric structures. The present article reports an ab initio improved van der Waals density functional (vdW-DF2) study devoted to the interactions associated with H 2 , CH 4 , and CO 2 adsorption in sI clathrate hydrate. The study provides the clathrate stability, diffusion, and energy storage of possible mixed gas occupancy in sI cages in the presence of H 2 . The results also provided the hydrogen energy landscapes and the estimated diffusion activation energy barriers to the large and small cage to be 0.181 and 0.685 eV, respectively. In addition, the results showed that the presence of CH 4 or CO 2 could enhance the storage capacity, thermodynamic stability, and hydrogen diffusion in sI clathrates. The volumetric storage, gravimetric storage, and molecular hydrogen content in H 2 –CH 4 binary sI clathrate are calculated to be 2.0 kW h/kg, and 1.8 kW h/L, and 5.0 wt%, respectively. These results are comparable to DOE targets of hydrogen storage. • CH 4 works as a thermodynamic promoter to stabilize clathrate for hydrogen storage. • Clathrate stability is improved by a double occupancy (H 2 –CO 2 ) of the large cage. • Double occupancy of the large cages facilitates H 2 diffusion. • H 2 –CH 4 sI clathrate energy storage can reach 2.0 kWh/kg and 1.8 kWh/L. • H 2 –CH 4 sI estimated capacity can meet DOE targets of volumetric and gravimetric energy storage.

A density functional study of electronic and optical properties of perovskite (CH3CH2NH3PbI3) for photovoltaic cell application

In this study, we have performed ab-initio screening of the ethylammonium cation-based hybrid perovskite ethylammonium lead iodide (CH3CH2NH3PbI3or EPI) as the prospective absorber material for fabricating cost-effective and energy-efficient photovoltaic devices. The extensively studied methylammonium lead iodide (CH3NH3PbI3 or MPI) exhibits high efficiency but has serious environmental and stability related concerns due to leakage of lead. Therefore, we intend to replace (CH3NH3+or M+) cation in MPI with (CH3CH2NH3+or E+) and expect that so formed perovskite EPI would prove to be an eco-friendlier and more stable photovoltaic absorber material. In this investigation, we have employed FP-LAPW+lo method under density functional theory as provided in WIEN2k simulation code. We have employed a more accurate Tb-mBJ exchange correlation potential to calculate physical properties like energy bandgap, density of states, optical parameters and SLME relevant to photovoltaic applications. According to the findings of this study, EPI is direct bandgap material with bandgap of 2.17 eV at k-point R with optical absorption coefficient higher than 104 cm−1, which endorses it as a suitable photovoltaic absorber material. The dependence of optical coefficients on angular frequency of incident electromagnetic radiation has also been discussed. The theoretical power conversion efficiency comes out to be 18.9%.

Cascade proton relays facilitate electron transfer across hydrogen‐bonding network

AbstractFunctioning as both hydrogen‐bonding donor and acceptor, the imidazole group of histidine holds a unique position in the proton transfer cascade of biological systems. For example, a histidine residue in the oxygen‐evolving photosystem II participates in the proton‐coupled electron transfer (PCET) reaction to facilitate light‐triggered one‐electron oxidation of a nearby tyrosine residue. As a minimalist synthetic model of such His–Tyr functional diad, three structural variants of benzimidazole–phenol conjugate were studied. We found that an increasing number of hydrogen bonds facilitate reversible one‐electron oxidation of the phenol ring. The reaction coordinates of this intriguing PCET process were mapped out by density functional theory computational studies to reveal oxidation‐driven conformational switching as an entry point to cascade proton relays stabilizing the phenoxyl radical. Strategic placement of hydrogen bonds thus tightly regulates the energy windows of electron transfer, which is an effective strategy for biological redoxphores of seemingly limited structural diversity.

Selective Photoactivation of Trithiocarbonates Mediated by Metal Naphthalocyanines and Overcoming Activation Barriers Using Thermal Energy.

Metal naphthalocyanines (MNcs) were demonstrated to be efficient photocatalysts to activate photoinduced electron-transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enabling well-controlled polymerization of (meth)acrylates under near-infrared (λ = 780 nm) light. Owing to their lower redox potential compared to previously explored photocatalysts, the activation of trithiocarbonate RAFT agents exhibited a unique selectivity that was dependent on the nature of the R group. Specifically, MNcs were capable in activating tertiary R group trithiocarbonates, whereas no activation of the trithiocarbonate possessing a secondary R group was observed. The combination of density functional theory calculations and experimental studies have revealed new mechanistic insights into the factors governing a PET-RAFT mechanism and explained this unique selectivity of MNcs toward tertiary carbon trithiocarbonates. Interestingly, by increasing the reaction temperature moderately (i.e., ∼15 °C), the energy barrier prohibiting the photoactivation of the trithiocarbonate with a secondary R group was overcome, enabling their successful activation.

Tin carbide monolayers decorated with alkali metal atoms for hydrogen storage

In this work, a density-functional study of hydrogen storage in tin carbide monolayers (2DSnC) decorated with alkali metals atoms (AM) such as Li, Na, and K, is reported. The most stable adsorption site for these alkali metal atoms on the 2DSnC is above a tin atom. The results indicate that the alkali metal atoms are chemisorbed on the 2DSnC and that electronic charge is transferred from the decorating atom to the 2DSnC. In all the studied cases, the hydrogen molecules are physisorbed on the AM-2DSnC (AM = Li, Na, and K) complexes and then these systems could be used for hydrogen storage. In particular, it is found that the K-2DSnC monolayer has the highest hydrogen-storage capacity, where a single potassium atom can adsorb up to 6 hydrogen molecules, followed by Na-2DSnC with 5 hydrogen molecules and Li-2DSnC with 3 hydrogen molecules. Finally, it can be estimated that when the K, Na and Li adatom-coverings respectively attain 40%, 44% and 70%, the hydrogen-storage gravimetric capacities of AM-2DSnC could overcome the US-DOE recommended target of 5.5 wt% for onboard automotive systems.

Insights into end‐capped modifications effect on the photovoltaic and optoelectronic properties of S‐shaped fullerene‐free acceptor molecules: A density functional theory computational study for organic solar cells

AbstractNon‐fused ring electron acceptors with different end‐capped substituents were designed to construct efficient organic solar cells (OSCs). End‐capped modification of acceptor materials is an efficient approach for developing high performance OSCs. In this report, five new S‐shaped fullerene‐free acceptor molecules (3P1 to 3P5) have been designed and examined through density function and time‐dependent density functional theories (TD‐DFTs). Designed molecules have twisted backbone with different out‐of‐plane rings that cause high solubility in dilute solvent. Different optoelectronic and photovoltaic properties of newly designed S‐shape molecules have been examined and explored through DFT tools. Orientation of frontier molecular orbitals (FMOs), light absorption range, exciton binding energy (Eb), oscillating strength (f), open circuit voltage (Voc), and transition density matrix (TDM) analysis have been performed for 3P1 to 3P5 molecules. Further, electron and hole reorganization energies are also estimated with excitation energy. Results of different computed parameters have recommended that these designed molecules are effective contributors for possible applications in the field of OSCs.