Search Results (15)

The activation and dissociation of O₂ molecules play a key role in the oxidation of toxic gas molecules and the oxygen reduction reaction (ORR) in hydrogen–oxygen fuel cells. The interactions between O₂ molecules and the surfaces of Fe-doped γ-graphyne were systematically explored, mainly adopting the combined method of the density functional theory with dispersion correction (DFT-D3) and the climbing image nudged elastic band (CI-NEB) method. The order of the formation energy values of these defective systems is E_f(Fe_C2) < E_f(Fe_C1) < E_f(Fe_D1) < E_f(V_C1) < E_f(V_D1) < E_f(V_C2) < E_f(Fe_D2) < E_f(V_D2), which indicates that the process of Fe dopant atoms substituting single-carbon atoms/double-carbon atoms is relatively easier than the formation of vacancy-like defects. The results of ab initio molecular dynamics (AIMD) simulations confirm that the doped systems can maintain structural stability at room temperature conditions. Fe-doped atoms transfer a certain amount of electrons to the adsorbed O₂ molecules, thereby causing an increase in the O-O bond length of the adsorbed O₂ molecules. The electrons obtained by the anti-bonding 2π* orbitals of the adsorbed O₂ molecules are mainly derived from the 3d orbitals of Fe atoms. There is a competitive relationship between the substrate’s carbon atoms and the adsorbed O₂ molecules for the charges transferred from Fe atoms. In the C1 and C2 systems, O₂ molecules have a greater advantage in electron accepting ability compared to the substrate’s carbon atoms. The elongation of O-O bonds and the amount of charge transfer exhibit a positive relationship. More electrons are transferred from Fe-3d orbitals to adsorbed O₂ molecules, occupying the 2π* orbitals of adsorbed O₂ molecules, further elongating the O-O chemical bond until it breaks. The dissociation process of adsorbed O₂ molecules on the surfaces of GY-Fe systems (C2 and D2 sites) involves very low energy barriers (0.016 eV for C2 and 0.12 eV for D2). Thus, our studies may provide useful insights for designing catalyst materials for oxidation reactions and the oxygen reduction reaction. Full article

The electronic and phonon bands of Skaergaardite are investigated using density functional theory (DFT) as implemented in Quantum ESPRESSO. Skaergaardite is a copper palladium mineral (CuPd) found in the Skaergaard intrusion with a CsCl-type (B2) structure. Due to its porous structure, it presents a large surface area available for interactions, which makes it a promising catalyst. The PBE-GGA functional with a Hubbard-like localized term (DFT+U) is combined with ultrasoft and norm-conserving pseudopotentials, and a conventional approach with a dense Monkhorst–Pack grid of k-points 12 × 12 × 12 is applied. The electronic valence bands are mainly constituted by 3d orbitals of Cu and 4d orbitals of Pd and a pseudo-gap can be recognized. With respect to DFT, DFT+U causes a general downward shift in the valence band. The acoustic and optical phonon branches are separated by a few cm⁻¹ gap at about 150 cm⁻¹ and show a density of state curve typical of ordered materials. These results highlight the reliability of DFT+U in studying bimetallic systems with scarce experimental benchmarks, offering insights into the behavior of Skaergaardite and its potential applications in material science such as reduction reactions and hydrogen storage. Full article

Hyperfine splittings play an important role in quantum information and spintronics applications. They allow for the readout of the spin qubits, while at the same time providing the dominant mechanism for the detrimental spin decoherence. Their exact knowledge is thus of prior relevance. In this work, we analytically investigate the relativistic effects on the hyperfine splittings of hydrogen-like atoms, including finite-size effects of the nucleis’ structure. We start from exact solutions of Dirac’s equation using different nuclear models, where the nucleus is approximated by (i) a point charge (Coulomb potential), (ii) a homogeneously charged full sphere, and (iii) a homogeneously charged spherical shell. Equivalent modelling has been done for the distribution of the nuclear magnetic moment. For the $1s$ ground state and $2s$ excited state of the one-electron systems ${}^1\mathrm{H}$, ${}^2\mathrm{H}$, ${}^3\mathrm{H}$, and ${}^3\mathrm{He}^{+}$, the calculated finite-size related hyperfine shifts are quite similar for the different structure models and in excellent agreement with those estimated by comparing QED and experiment. This holds also in a simplified approach where relativistic wave functions from a Coulomb potential combined with spherical-shell distributed nuclear magnetic moments promises an improved treatment without the need for an explicit solution of Dirac’s equation within the nuclear core. Larger differences between different nuclear structure models are found in the case of the anisotropic $2p_{3/2}$ orbitals of hydrogen, rendering these excited states as promising reference systems for exploring the proton structure. Full article

Two-dimensional (2D) materials have emerged as a frontier in materials science, offering unique properties due to their atomically thin nature. Among these materials, bismuthene stands out due to its exceptional optical, electronic, and catalytic characteristics. Bismuthene exhibits high charge carrier mobility, stability, and a tunable bandgap (0.3–1.0 eV), making it highly suitable for applications in transistors, spintronics, biomedicine, and photocatalysis. This work explores the so far reported synthesis methods for obtaining 2D bismuthene, including bottom-up approaches like chemical vapor deposition and molecular beam epitaxy, and top-down methods such as liquid-phase exfoliation and mechanical exfoliation. Recent advancements in understanding 2D bismuthene structural phases, electronic properties modulated by spin-orbit coupling, and its potential applications in next-generation photocatalysts are also reviewed. As is retrieved by our literature review, 2D bismuthene shows great promise for addressing significant environmental challenges. For instance, in CO₂ reduction, integrating bismuthene into 2D/2D heterostructures enhances electron transfer efficiency, thereby improving selectivity toward valuable products, such as CH₄ and formic acid. In organic pollutant degradation, bismuth subcarbonate (Bi₂O₂CO₃) nanosheets, obtained from 2D bismuthene, have demonstrated high photocatalytic degradation of antibiotics under visible light irradiation, due to their increased surface area and efficient generation of reactive species. Moreover, bismuthene-based materials exhibit potential in the photocatalytic water-splitting process for hydrogen production, overcoming issues associated with UV-light dependence and sacrificial agent usage. This review underscores the versatile applications of 2D bismuthene in advancing photocatalytic technologies, offering insights into future research directions and potential industrial applications. Full article

Over a wide and partly overlapping energy range, the single-electron capture cross-sections for collisions of metastable ${\mathrm{Sn}}^{2+}(5s5p \mathrm{P}_o^3)$ (${\mathrm{Sn}}^{2+\ast }$) ions with ${\mathrm{H}}_2$ molecules were measured (0.1–10 keV) and calculated (0.3–1000 keV). The semi-classical calculations use a close-coupling method on a basis of electronic wavefunctions of the (SnH₂)²⁺ system. The experimental cross-sections were extracted from double collisions in a crossed-beam experiment of ${\mathrm{Sn}}^{3+}$ with ${\mathrm{H}}_2$. The measured capture cross-sections for ${\mathrm{Sn}}^{2+\ast }$ show good agreement with the calculations between 2 and 10 keV, but increase toward lower energies, whereas the calculations decrease. Additional Landau–Zener calculations were performed and show that the inclusion of spin-orbit splitting cannot explain the large cross-sections at the lowest energies which we now assume to be likely due to vibrational effects in the molecular hydrogen target. Full article

Understanding the role of 3CLpro protease for SARS-CoV-2 replication and knowing the potential of flavonoid molecules like rutin, myricetin, and baicalein against 3CLpro justify an investigation into their inhibition. This study investigates possible bonds and reactivity descriptors of rutin, myricetin, and baicalein through conformational and electronic properties. Density functional theory was used to determine possible interactions. Analyses were carried out through the molecular electrostatic potential, electron localization function, Fukui function descriptors based on frontier orbitals, and non-covalent interactions. A docking study was performed using a resolution of 1.55 Å for 3CLpro to analyze the interactions of rutin, myricetin, and baicalein. Scores of structures showed that rutin is the best ligand, followed by myricetin and baicalein. Docking studies showed that baicalein and rutin can establish effective interactions with residues of the catalytic dyad (Cys145 and His41), but just rutin forms a hydrogen bond. Myricetin, in turn, could not establish an effective interaction with Cys145. Baicalein interaction arose with active residues such as Arg188, Val186, Gln189, and Gln192. Interactions of rutin and myricetin with Arg188 and Gln189 were also found. A critical interaction was observed only for rutin with the hydroxyls of ring A with His41, and also for Cys145 with rings B and C, which is probably related to the highest score of rutin. Full article

Structures characterized by the trigonal coordination of the gallium center that interacts with electron rich carbon sites are described. These interactions may be classified as Ga···C triel bonds. Their properties are analyzed in this study since these interactions may be important in numerous chemical processes including catalytical activities; additionally, geometrical parameters of corresponding species are described. The Ga···C triel bonds discussed here, categorized also as the π-hole bonds, do not change the trigonal configuration of the gallium center into the tetrahedral one despite total interactions in dimers being strong; however, the main contribution to the stabilization of corresponding structures comes from the electrostatic forces. The systems analyzed theoretically here come from crystal structures since the Cambridge Structural Database, CSD, search was performed to find structures where the gallium center linked to CC bonds of Lewis base units occurs. The majority structures found in CSD are characterized by parallel, stacking-like arrangements of species containing the Ga-centers. The theoretical results show that interactions within dimers are not classified as the three-centers links as in a case of typical hydrogen bonds and numerous other interactions. The total interactions in dimers analyzed here consist of several local intermolecular atom–atom interactions; these are mainly the Ga···C links. The DFT results are supported in this study by calculations with the use of the quantum theory of atoms in molecules, QTAIM, the natural bond orbital, NBO, and the energy decomposition analysis, EDA, approaches. Full article

A two-dimensional graphene-like carbon nitride (g-CN) monolayer decorated with the superatomic cluster NLi₄ was studied for reversible hydrogen storage by first-principles calculations. Molecular dynamics simulations show that the g-CN monolayer has good thermal stability at room temperature. The NLi₄ is firmly anchored on the g-CN monolayer with a binding energy of −6.35 eV. Electronic charges are transferred from the Li atoms of NLi₄ to the g-CN monolayer, mainly due to the hybridization of Li(2s), C(2p), and N(2p) orbitals. Consequently, a spatial local electrostatic field is formed around NLi₄, leading to polarization of the adsorbed hydrogen molecules and further enhancing the electrostatic interactions between the Li atoms and hydrogen. Each NLi₄ can adsorb nine hydrogen molecules with average adsorption energies between −0.152 eV/H₂ and −0.237 eV/H₂. This range is within the reversible hydrogen storage energy window. Moreover, the highest achieved gravimetric capacity is up to 9.2 wt%, which is superior to the 5.5 wt% target set by the U.S. Department of Energy. This study shows that g-CN monolayers decorated with NLi₄ are a good candidate for reversible hydrogen storage. Full article

This work explores the electronic structure as well as the reactivity of singlet diradicals, making use of multistate density functional theory (MSDFT). In particular, we show that a minimal active space of two electrons in two orbitals is adequate to treat the relative energies of the singlet and triplet adiabatic ground state as well as the first singlet excited state in many cases. This is plausible because dynamic correlation is included in the first place in the optimization of orbitals in each determinant state via block-localized Kohn–Sham density functional theory. In addition, molecular fragment, i.e., block-localized Kohn–Sham orbitals, are optimized separately for each determinant, providing a variational diabatic representation of valence bond-like states, which are subsequently used in nonorthogonal state interactions (NOSIs). The computational procedure and its performance are illustrated on some prototypical diradical species. It is shown that NOSI calculations in MSDFT can be used to model bond dissociation and hydrogen-atom transfer reactions, employing a minimal number of configuration state functions as the basis states. For p- and s-types of diradicals, the closed-shell diradicals are found to be more reactive than the open-shell ones due to a larger diabatic coupling with the final product state. Such a diabatic representation may be useful to define reaction coordinates for electron transfer, proton transfer and coupled electron and proton transfer reactions in condensed-phase simulations. Full article

Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)–Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)₂·2H₂O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel [Zn(μ-Pip)₂(4-Acpy)]₂ (1); a mixture of one dimer and two monomers [Zn(µ-Pip)(Pip)(Isn)₂]₂·2[Zn(Pip)₂(HPip)(Isn)]·2MeOH (2); and two dimers [Cd(μ-Pip)(Pip)(4-Acpy)₂]₂ (3) and [Cd(μ-Pip)(Pip)(Isn)₂]₂·MeOH (4). They exhibit bridged (1, µ₂-η¹:η¹), bridged, chelated and monodentated (2, µ₂-η¹:η¹, µ₁-η¹:η¹ and µ₁-η¹), or simultaneously bridged and chelated (3 and 4, µ₂-η²:η¹) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations. Full article

Atoms are proved to be semi-classical electronic systems in the sense of closeness of their exact quantum electron energy spectrum with that calculated within semi-classical approximation. Introduced semi-classical model of atom represents the wave functions of bounded in atom electrons in form of hydrogen-like atomic orbitals with explicitly defined effective charge numbers. The hydrogen-like electron orbitals of constituting condensed matter atoms are used to calculate the matrix elements of the secular equation determining the condensed matter electronic structure in the linear-combination-of-atomic-orbitals (LCAO) approach. Preliminary test calculations are conducted for boron B atom and diboron B₂ molecule electron systems. Full article

According to the existing paradigm, helium atoms and helium-like ions (hereafter, heliumic systems) in a relatively weak external static electric field do not exhibit the linear Stark effect—in distinction to hydrogen atoms and hydrogen-like ions. In the present paper we consider the classical dynamics of a muonic-electronic heliumic system in Rydberg states–starting from the concept from our previous paper. We show that there are two states of the system where the averaged electric dipole moment is non-zero. Consequently, in these states the heliumic system should exhibit the linear Stark effect even in a vanishingly small electric field, which is a counter-intuitive result. We also demonstrate the possibility of controlling the overall precession of the electronic orbit by an external electric field. In particular, we show the existence of a critical value of the external electric field that would “kill” the precession and make the electronic orbit stationary. This is another counter-intuitive result. We calculate analytically the value of the critical field and show that it is typically smaller or even much smaller than 1 V/cm. Full article

The application of donor-acceptor (D-A) conjugated polymer catalysts for hydrogen evolution reaction (HER) has shown great promise because of the tunability of such catalysts to have desired properties. Herein, we synthesized two polymer catalysts: poly[4,4′-(9-(4-aminophenyl)-9H-carbazole-3,6-diamine-alt-5-oxido-5-phenylbenzo[b]phosphindole-3,7-diyl)dibenzaldehyde] (PCzPO) and poly[N¹,N¹-bis(4-amino-2-fluorophenyl)-2-fluorobenzene-1,4-diamine-alt-5-oxido-5-phenylbenzo[b]phosphindole-3,7-diyl)dibenzaldehyde] (PNoFPO). The UV-vis absorption spectra showed that the less planar structure and the presence of electronegative fluorine atoms in the donor group of PNoFPO led to a higher optical gap compared to PCzPO, leading to almost five times faster HER rate using PCzPO compared to PNoFPO. However, density functional theory (DFT) calculations show that the frontier orbitals and the highest occupied molecular orbitals – lowest unoccupied molecular orbitals (HOMO-LUMO) gaps of PCzPO and PNoFPO D-A moiety models are very similar, such that, during light absorption, electrons move from donor to acceptor group where proton binding is preferred to happen thereafter. For both PCzPO and PNoFPO D-A moieties, H₂ formation through an intramolecular reaction with a barrier of 0.6–0.7 eV, likely occurs at the acceptor group atoms where protons bind through electrostatic interaction. The intermolecular reaction has nearly zero activation energy but is expected to occur only when the repulsion is low between separate polymers chains. Finally, experimental and DFT results reveal the importance of extended configurations of D-A polymers on HER rate. Full article

Flavonoids are known for their antiradical capacity, and this ability is strongly structure-dependent. In this research, the activity of flavones and flavonols in a water solvent was studied with the density functional theory methods. These included examination of flavonoids’ molecular and radical structures with natural bonding orbitals analysis, spin density analysis and frontier molecular orbitals theory. Calculations of determinants were performed: specific, for the three possible mechanisms of action—hydrogen atom transfer (HAT), electron transfer–proton transfer (ETPT) and sequential proton loss electron transfer (SPLET); and the unspecific—reorganization enthalpy (RE) and hydrogen abstraction enthalpy (HAE). Intramolecular hydrogen bonding, catechol moiety activity and the probability of electron density swap between rings were all established. Hydrogen bonding seems to be much more important than the conjugation effect, because some structures tends to form more intramolecular hydrogen bonds instead of being completely planar. The very first hydrogen abstraction mechanism in a water solvent is SPLET, and the most privileged abstraction site, indicated by HAE, can be associated with the C3 hydroxyl group of flavonols and C4’ hydroxyl group of flavones. For the catechol moiety, an intramolecular reorganization to an o-benzoquinone-like structure occurs, and the ETPT is favored as the second abstraction mechanism. Full article

Human chymase is a very important target for the treatment of cardiovascular diseases. Using a series of theoretical methods like pharmacophore modeling, database screening, molecular docking and Density Functional Theory (DFT) calculations, an investigation for identification of novel chymase inhibitors, and to specify the key factors crucial for the binding and interaction between chymase and inhibitors is performed. A highly correlating (r = 0.942) pharmacophore model (Hypo1) with two hydrogen bond acceptors, and three hydrophobic aromatic features is generated. After successfully validating “Hypo1”, it is further applied in database screening. Hit compounds are subjected to various drug-like filtrations and molecular docking studies. Finally, three structurally diverse compounds with high GOLD fitness scores and interactions with key active site amino acids are identified as potent chymase hits. Moreover, DFT study is performed which confirms very clear trends between electronic properties and inhibitory activity (IC₅₀) data thus successfully validating “Hypo1” by DFT method. Therefore, this research exertion can be helpful in the development of new potent hits for chymase. In addition, the combinational use of docking, orbital energies and molecular electrostatic potential analysis is also demonstrated as a good endeavor to gain an insight into the interaction between chymase and inhibitors. Full article