Density Functional Study Research Articles

Reactivity of a Hexaaryldiboron(6) Dianion as Boryl Radical Anions.

Our study unveils a novel approach to accessing boryl radicals through the spontaneous homolytic cleavage of B-B bonds. We synthesized a hexaaryl-substituted diboron(6) dianion, 1, via the reductive B-B coupling of 9-borafluorene. Intriguingly, compound 1 exhibits the ability to undergo homolytic B-B bond cleavage, leading to the formation of boryl radical anions, as confirmed by EPR studies, in the presence of the 2.2.2-cryptand at room temperature. Moreover, it directly reacts with diphenylacetylene, producing an unprecedented 1,6-diborylated allene species, where the phenyl ring is dearomatized. Density functional theory computational studies suggest that homolytic B-B bond cleavage is favored in the reaction path, and the formation of the boryl radical anion is crucial for dearomatization. Additionally, it achieves the dearomative diborylation of anthracene and the activation of elemental sulfur/selenium under mild conditions. The borylation products have been successfully characterized by NMR spectra, HRMS, and X-ray single-crystal diffraction.

Yielding high photovoltaic conversion efficiency by Pd-decoration on Si-based interface: A density-functional theory study

There has been showing great interest in boosting the performance of III-V/Si multi-junction solar cell, which is low-cost and offering high photovoltaic conversion efficiency. Adding noble-metal nano-array at the interface between the Si and III-V materials is one of most effective ways. This theoretical work comprehensively studied the atomic structure, electronic properties, and optical response of Pd-decoration on the Si(111) surface by using density-functional theory calculations. The structural stability calculations showed that Pd atoms could exist on Si surface in many forms. The calculated differential charge density with Bader charge showed that the charge transfer between Pd and Si atoms would increase the generation of electron-hole pairs. At the same time, Pd-decoration could reduce the work function and improve the optical conductivity of Si surface. In addition, the modification of Pd atoms would create new energy levels near the Fermi level in the band gap of Si surface. These energy levels enable Si bottom cell to undergo electron inter-band transitions under weak light irradiation, improving the utilization of weak light. This work provided a micro physical explanation for the improvement of III-V/Si solar cell by using noble-metal nano-array.

Understanding the effect of refractory metal chemistry on the stacking fault energy and mechanical property of Cantor-based multi-principal element alloys

Multi-principal-element alloys (MPEAs) based on 3d-transition metals show remarkable mechanical properties. The stacking fault energy (SFE) in face-centered cubic (fcc) alloys is a critical property that controls underlying deformation mechanisms and mechanical response. Here, we present an exhaustive density-functional theory study on refractory- and copper-reinforced Cantor-based systems to ascertain the effects of refractory metal chemistry on SFE. We find that even a small percent change in refractory metal composition significantly changes SFEs, which correlates favorably with features like electronegativity variance, size effect, and heat of fusion. For fcc MPEAs, we also detail the changes in mechanical properties, such as bulk, Young's, and shear moduli, as well as yield strength. A Labusch-type solute-solution-strengthening model was used to evaluate the temperature-dependent yield strength, which, combined with SFE, provides a design guide for high-performance alloys. We also analyzed the electronic structures of two down-selected alloys to reveal the underlying origin of optimal SFE and strength range in refractory-reinforced fcc MPEAs. These new insights on tuning SFEs and modifying composition-structure-property correlation in refractory- and copper-reinforced MPEAs by chemical disorder, provide a chemical route to tune twinning- and transformation-induced plasticity behavior.

Time-dependent density-functional theory study on nonlocal electron stopping for inertial confinement fusion

Understanding laser–target coupling is of the utmost importance for achieving high performance in laser-direct-drive (LDD) inertial confinement fusion (ICF) experiments. Thus, accurate modeling of electron transport and deposition through ICF-relevant materials and conditions is necessary to quantify the total thermal conduction and ablation. The stopping range is a key transport quantity used in thermal conduction models; in this work, we review the overall role that the electron mean free path (MFP) plays in thermal conduction and hydrodynamic simulations. The currently used modified Lee–More model employs various physics approximations. We discuss a recent model that uses time-dependent density functional theory (TD-DFT) to eliminate these approximations in both the calculation of the electron stopping power and corresponding MFP in conduction zone polystyrene (CH) plasma. In general, the TD-DFT calculations showed a larger MFP (lower stopping power) than the standard modified Lee–More model. Using the TD-DFT results, an analytical model for the electron deposition range, λTD−DFT(ρ,T,K), was devised for CH plasmas between ρ=[0.05−1.05] g/cm3, kBT=[100−1000] eV. We implemented this model into LILAC, for simulations of a National Ignition Facility-scale LDD implosion and compared key physics quantities to ones obtained by simulations using the standard model. The implications of the obtained results and the path moving forward to calculate this same quantity in conduction-zone deuterium–tritium plasmas are further discussed, to hopefully close the understanding gap for laser target coupling in LDD-ICF simulations.

High Thermoelectric Performance of Ge–Sb–Te Nanosheets: A Density Functional Study

High Thermoelectric Performance of Ge–Sb–Te Nanosheets: A Density Functional Study

Density Functional Study of Electrocatalytic Carbon Dioxide Reduction in Fourth-Period Transition Metal-Tetrahydroxyquinone Organic Framework.

This study investigates the utilisation of organometallic network frameworks composed of fourth-period transition metals and tetrahydroxyquinone (THQ) in electrocatalytic CO2 reduction. Density functional theory (DFT) calculations were employed in analysing binding energies, as well as the stabilities of metal atoms within the THQ frameworks, for transition metal TM-THQs ranging from Y to Cd. The findings demonstrate how metal atoms could be effectively dispersed and held within the THQ frameworks due to sufficiently high binding energies. Most TM-THQ frameworks exhibited favourable selectivity towards CO2 reduction, except for Tc and Ru, which experienced competition from hydrogen evolution reaction (HER) and required solution environments with pH values greater than 5.716 and 8.819, respectively, to exhibit CO2RR selectivity. Notably, the primary product of Y, Ag, and Cd was HCOOH; Mo produced HCHO; Pd yielded CO; and Zr, Nb, Tc, Ru, and Rh predominantly generated CH4. Among the studied frameworks, Zr-THQ displayed values of 1.212 V and 1.043 V, corresponding to the highest limiting potential and overpotential, respectively, while other metal-organic frameworks displayed relatively low ranges of overpotentials from 0.179 V to 0.949 V. Consequently, it is predicted that the TM-THQ framework constructed using a fourth-period transition metal and tetrahydroxyquinone exhibits robust electrocatalytic reduction of CO2 catalytic activity.

Coverage-dependent adsorption of n-hexane and isopropanol on silica: A density-functional study

This study delves into the adsorption behavior of both polar and non-polar molecules on silica surfaces, spanning a range from low coverage to full adsorption scenarios. Our results reveal that isopropanol exhibits a self-competitive adsorption mechanism on the surface. However, due to its thermodynamic stability, we anticipate fully covered pores under experimental conditions. In contrast, n-hexane demonstrates a substantial interaction with the hydrophilic substrate, displaying an enhanced adsorption effect whereby the adsorption gets stronger with an increasing number of molecules adhering to the pore’s surface. As a consequence, we predict a complete coverage of the pores under experimental conditions, accompanied by a discernible reduction in the mobility of these attached molecules. This observation carries significance, as alkanes are typically employed as probing molecules for measuring the geometric tortuosity of silica pores, assuming a reflective surface. Caution is advised, particularly for pores with thin diameters, in the order of a few molecular sizes.

Conversion of the greenhouse gases CH4 and CO2 to CH3COOH using transition metal Clusters: Two birds with one stone

Density functional theoretical studies are performed to investigate the conversion of carbon dioxide and methane to acetic acid using group 10 transition metal clusters in their free and carbon-supported states. The adsorption of CH4 is more feasible than CO2 for most of the clusters and the reaction is initiated with the adsorption of CH4 over the catalysts. Energy barrier for the reaction is reduced significantly using the clusters compared to that in free state which is further reduced when coronene is used as a carbon support. Among various metal clusters, the barrier is found to be the lowest for Ni3.

Experimental and density-functional theory simulation studies on the surface of Mn/Pb-activated scheelite

The results of this study indicate that lead and manganese ions can serve as effective activators for the flotation of scheelite using benzohydroxamic acid (BHA) collectors, and even the addition of a small amount of lead ions can significantly improve the recovery rate of scheelite. The roughness of scheelite treated with binary activators and BHA is 8.19 nm and 2.1 nm higher than that the roughness values of scheelite treated with Mn(NO3)2 and Pb(NO3)2 alone, respectively. The adsorbed products are uniformly distributed on the scheelite surface, and the adsorption forms a “strip-like and dot-like” morphology. Lead ions are mainly adsorbed on mineral surfaces through Pb-O(H)-Ca, and manganese ions are mainly adsorbed in the form of Mn (II) species (i.e., Mn-O-Ca). In the presence of BHA, compared with scheelite treated with manganese and lead ions alone, scheelite treated with binary activators exhibits a more negative zeta potential on its surface, a higher contact angle of 89.30°, and a more pronounced infrared adsorption characteristic peak (C-N-O). DFT calculations confirm that lead ions and manganese ions are adsorbed on the surface of scheelite (112) in the forms of Pb-O-W, Mn-O-W, and Mn-O(H)-Ca. Moreover, the Pb-O(H)-Mn structure covers the surface atoms of scheelite, forming a layer of active substance on the surface of scheelite, and the structure is more stable than in the case of single ion activation, according to the BHA adsorption calculations.

Synthesis, structural characterization of phenoxo-bridged zinc(II) complexes and their binding interaction with the spike protein of SARS-CoV-2

The research article reports the synthesis and structural study of the optimized geometry of selenium (Se) bearing 24- and 28- membered macrocyclic Schiff bases, LaH2 , LbH2 and their reactions with zinc metal ion. The reactions of the macrocyclic Schiff bases with ZnCl2 in 1:2 molar ratios result in the formation of bimetallic Zn(II) complexes having molecular composition [Se{(CH2)2N = CPh(4-CH3-C6H2O) PhC = O}2 · Zn2Cl2], (1) and [Se{(CH2)3N = CPh(4-CH3-C6H2O)PhC = O}2 · Zn2Cl2], (2). Moreover, as confirmed by various physico-chemical techniques such as elemental analysis, UV–Vis, FTIR,1H NMR, and mass spectrometry, the proligands underwent partial hydrolytic cleavage at one of the C = N positions and behave like hexadentate (N2O4) ligands binding to two Zn(II) ions via bridging through the Ophenolic atoms, which results in a square pyramidal geometry around Zn(II) with the chlorine atom occupying axial positions. Further, following density functional study, the stable optimized configuration of the Schiff bases LaH2 and LbH2 is found to adopt bowl shape geometry. Conversely, in molecular docking studies, the synthesized complex 1 exhibits a significantly stronger binding affinity (−8.7 kcal/mol) to the spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) as compared to the common coronavirus disease 2019 (COVID-19) treatment drugs such as chloroquine, hydroxychloroquine, and remdesivir with activity percentage showing more than 20% overall effectiveness than remdesivir and thus indicating its potential for COVID-19 therapeutics.

Effect of Fatty Acid Unsaturation on the Intermolecular Weak Interaction at the Low-Rank Coal-Water Interface: Density Functional Theory Calculations and Experimental Study.

The study on the effect of fatty acid saturation on low-rank coal (LRC) flotation is still limited. In this investigation, density functional theory (DFT) combined with Zeta potential and Fourier transform infrared spectroscopy (FTIR) was used to study the mechanism of intermolecular weak interaction at the LRC-water interface of fatty acids (decanoic acid (DA), undecylenic acid (UA), and phenyl propionic acid (PA)) with different saturations and different dodecane (D) composition hydrocarbon oil-fatty acid mixed collectors (D-DA, D-UA, D-PA). The findings demonstrated that the hydrogen bond interaction and electrostatic interaction between the UA/PA with unsaturated bonded carbon chains and the LRC molecular fragments/water molecules were stronger than DA without a saturated bond carbon chain, and UA/PA strengthened its interaction with water molecules on the whole, even PA molecules would preferentially interact with water molecules. The unsaturated bond had a minimal impact on the adsorption of the LRC hydrophobic site, and the strength of the hydrogen bond between the mixed collector and LRC is D-DA > D-UA > D-PA. In the actual flotation process, the strong hydrogen bonding and electrostatic interaction between UA/PA and water molecules weaken the collection performance of the mixed collector D-UA/D-PA for LRC, which also confirmed the research results of DFT, FTIR, and Zeta.

Feeling the strain: Enhancing the thermodynamics characteristics of magnesium nickel hydride Mg2NiH4 for hydrogen storage applications through strain engineering

This work is based on density functional theory (DFT) and studies the structural, electronic, thermodynamic properties and dehydrogenation kinetics of the hydride Mg2NiH4 under different uniaxial and biaxial strain applied to Mg2Ni or Mg2NiH4. structural properties are first studied based on generalized gradient (GGA) and local density (LDA). Thermodynamic and electronic properties and dehydrogenation kinetics are then studied using the GGA method based on the Perdew-Burke-Ernzerhor (PPE) approximation. The results obtained show that uniaxial/biaxial tensile and compressive strains are capable of inducing structural deformation by increasing the value of the strain step on both Mg2Ni and Mg2NiH4, and that these strains applied to Mg2NiH4 are capable of reducing the stability of the system more than strains applied to Mg2Ni, due to the contribution of strain energy. More specifically, it lowers the enthalpy of formation to −40 kJ/mol.H2 under compressive strain ε = −7.5% or biaxial tensile strain ε = +7.8%, which corresponds exactly to the ideal value suggested by the US Department of Energy (DOE) for materials suitable for hydrogen storage. And the decomposition temperature fell within the fuel cell operating range (PEM) of 289–393 K. On the other hand, under uniaxial and biaxial strains, the activation energy of hydrogen atom diffusion in Mg2NiH4 varied between 0.40 eV and 0.22 eV, resulting in a remarkable improvement in dehydrogenation properties. Analysis of the total (TDOS) and partial (PDOS) density curves shows that the Mg2NiH4 system has a metallic characteristic, and that this characteristic is maintained by increasing the strain pitch, with a variation in the energy width of the valence band.

Halogen-Bond-Promoted Direct Cross-Coupling of Trifluoromethylated Alkyl Bromides with Coumarins/Quinolinones: Unraveling Trifluoromethyl Effects.

This study introduces a novel approach involving XB-mediated cross-coupling of α-trifluoromethylated alkyl bromides with coumarins and quinolinones under visible light irradiation. Both density functional theory (DFT) calculations and experimental studies converge to suggest that the noncovalent interaction between alkyl bromides and DMAP, intensified by the α-trifluoromethyl group, plays a pivotal role in facilitating this chemoselective reaction.

Exploring multicomponent perovskites ReXO[formula omitted] (Re=Sm, Eu, Gd and X=Ti, Cr, Ni and Cu): Channeling properties through alloying

Multi-component systems involving the high-entropy and the medium-entropy perovskites stimulate the incorporation of additional components to facilitate the simultaneous customization of a range of properties, thereby unlocking their potential for novel functionalities. A new class of multicomponent perovskite oxides with the participation of rare earth elements has been synthesized. The three compositions which were produced by mechanical alloying involved Sm(Ti0.18Cr0.23Ni0.29Cu0.30)O3, Eu(Ti0.18Cr0.23Ni0.29Cu0.30)O3 and Gd(Ti0.18Cr0.23Ni0.27Cu0.32)O3. The Goldschmidt’s tolerance factor predicts the stability of the multicomponent perovskite crystal structures. Furthermore, to provide a theoretical viewpoint on the above perovskites, a density-functional study of all the structures along with the single-metallic perovskites has been performed. The formation energy of the structures (three multi-component and 12 single-metallic perovskites) confirms the stability and also their formation. Furthermore, the energy gap detected in the spin-down channels of the multicomponent materials suggests a promising potential for these systems as a spin filter in spintronic applications. The magnetic characteristic could be helpful for tuning the physical characteristics of the perovskites and could modify drastically their transport properties.

Unraveling Bulk versus Surface Passivation Effects in Highly Efficient p–i–n Perovskite Solar Cells Using Thiophene‐Based Cations

Defect passivation is nowadays considered a must‐have route for high‐efficiency perovskite solar cells. However, a general rule that correlates the choice of passivating agents with performance enhancements is still missing. Herein, two different thiophene salts that are used as passivating agents are compared, namely thiophene methylammonium chloride and thiophene ethylammonium chloride (TEACl), which are used for the passivation of bulk and surface defects in triple‐cation‐based metal halide perovskites. First, it is observed that the surface passivation method leads to better device performances reaching a power conversion efficiency of 23.56%, with reduced voltage losses and increased fill factor when compared with the reference. Second, it is demonstrated that the chemical structure of the cation dictates its capability either in passivating bulk defects effectively or to form a superficial two‐dimensional/three‐dimensional heterostructure, which happens only for the TEACl case. The chemical composition and the cation dimension are responsible for device performance enhancement as observed by a joint spectroscopic and density functional theory simulations study, providing rational guidelines for further smart device design.

Boosting hydrogen storage capacity in modified-graphdiyne structures: A comprehensive density functional study

Graphdiyne (GDY) is a recently discovered two-dimensional carbon allotrope that holds significant promise for applications in hydrogen adsorption and storage technology. This study investigates the impact of nitrogen doping and sodium decoration on the hydrogen adsorption capacity of GDY nanosheets while examining their influence on electronic and structural properties. Various deliberate impurities are introduced to create modified-GDY structures. Nitrogen doping triggers a transition from a semiconductor to a semi-metallic state, driven by differences in electronegativity and adjustments in bond lengths. Cohesive energy (Ecoh) is found to be −7.231 eV for the most stable N-doped GDY. In contrast, sodium decoration enhances conduction by modifying charge distribution. The other most stable structures are Na-decorated GDY with Eads of −3.804 eV and N, Na-decorated GDY with −3.347 eV. Modified-GDY structures exhibit higher hydrogen adsorption energies compared to pristine GDY, with N-doped GDY displaying the highest energy levels (Eads = −0.455 eV). Maximum hydrogen adsorption capacities are assessed for each structure, and a notable improvement is observed in Na-decorated GDY (19 H2), significantly enhancing the storage capacity to 13.8 wt%, which shows a 10.21 wt% increase in H2 adsorption compared to pure GDY (3.59 wt%). These findings underscore the potential of modified-GDY for hydrogen storage applications, highlighting the effectiveness of structural carbon modification in enhancing hydrogen adsorption capacity.

Leveraging Nonstrained C-C Bonds for Selective Carboacylation of an Unactivated Alkyne via Transient Dearomatization.

Carboacylation of an unsaturated bond represents a powerful transformation. However, only a few examples of carboacylation of alkyne have been reported through C-C bond scission and reconnection. Here, we report a method of carboacylation of an unactivated alkyne by utilizing nonstrained C-C bonds under gold(I) catalysis. The density functional theory computational and experimental studies reveal that the reaction proceeds through a C-to-C formal 1,3-acyl migration via a solvent cage-nested acylium cation.

A hybrid density functional study of tensile-induced changes in phonon dispersion, electronic structure and optical absorption of bilayer BN for optoelectronic applications

The electronic, phonon dispersion and optical properties of bilayer BN have been investigated with density functional theory (DFT) calculations. Interestingly, applying the biaxial strain of 4% converts the indirect band gap of bilayer BN to a direct band gap. We show that the interaction between the BN layers results in the removal of two-fold degeneracy and separation of ZA and ZO phonon modes near the Γ point. Across the entire range of applied biaxial tensile strains, the bilayer BN exhibits a dynamically stable behavior. The phonon bandgap of bilayer BN decreases under tensile strain. The bilayer BN has strong adsorption in the UV region and the optical absorption peaks are red-shifted by applying the tensile strain. These findings are essential for the strain engineering of bilayer BN and future fabrication of flexible electronic and optoelectronic devices.

CVD grown bi-layer MoS2 as SERS substrate: Nanomolar detection of R6G and temperature response

The two-dimensional bi-layer MoS2 is less investigated as compared to monolayer and few-layer (4–6 layers) MoS2 for fundamental aspects and applications such as photodetectors, transistors, etc. In the present work, we prepare triangular-shaped bi-layer MoS2 over SiO2/Si substrate via chemical vapour deposition (CVD) technique for surface enhanced Raman scattering (SERS) based detection of Rhodamine 6G (R6G). We perform density functional theory calculations and spectroscopy studies to investigate the semiconducting feature of bi-layer MoS2. We demonstrate the nanomolar concentration (10-9 M) limit for R6G detection at room temperature using pristine bi-layer MoS2 as SERS substrate. Further, we also examine the cryogenic response of the SERS detection of R6G with bi-layer MoS2 for the first time. The high detection limit of CVD-grown bi-layer MoS2 is ascribed to the charge transfer enabled via vibronic coupling between MoS2 and R6G molecules. This study paves the way for cryogenic-based SERS sensing.

A numerical Poisson solver with improved radial solutions for a self-consistent locally scaled self-interaction correction method

The universal applicability of density functional approximations is limited by self-interaction error made by these functionals. Recently, a novel one-electron self-interaction-correction (SIC) method that uses an iso-orbital indicator to apply the SIC at each point in space by scaling the exchange-correlation and Coulomb energy densities was proposed. The locally scaled SIC (LSIC) method is exact for the one-electron densities, and unlike the well-known Perdew–Zunger SIC (PZSIC) method recovers the uniform electron gas limit of the uncorrected density functional approximation, and reduces to PZSIC method as a special case when isoorbital indicator is set to the unity. Here, we present a numerical scheme that we have adopted to evaluate the Coulomb potential of the electron density scaled by the iso-orbital indicator required for the self-consistent LSIC calculations. After analyzing the behavior of the finite difference method (FDM) and the green function solution to the radial part of the Poisson equation, we adopt a hybrid approach that uses the FDM for the Coulomb potential due to the monopole and the GF for all higher-order terms. The performance of the resultant hybrid method is assessed using a variety of systems. The results show improved accuracy than earlier numerical schemes. We also find that, even with a generic set of radial grid parameters, accurate energy differences can be obtained using a numerical Coulomb solver in standard density functional studies.