International Journal of Quantum Chemistry最新文献

The collision reaction process of Si⁺ ions with HD molecules was studied using the time-dependent wave packet method within the energy range of 1.0–3.0 eV. Theoretical research results show that, except in the lower energy range, throughout the whole collision energy range studied, the competitive ability of the D + SiH⁺ product channel is stronger than that of the H + SiD⁺ channel. The comparison of integral cross sections with experimental results indicates that the results for the D + SiH⁺ and H + SiD⁺ channels are in general good agreement with the experimental values. The differential cross sections demonstrated that the angular distributions of products in both the H + SiD⁺ and D + SiH⁺ channels are almost forward–backward symmetric in the low collision energy range and primarily forward scattering at high collision energies. This indicates that as the collision energy increases, the reaction mechanism shifts from an insertion mechanism to a stripping mechanism.

Spontaneous time-reversal symmetry breaking phases are highly desirable due to their unique physical characteristics, low-dissipation electronic and spin responses, and potential applications in information technology. Altermagnets are distinguished by their unique spin-splitting properties that are not governed by conventional exchange interactions but instead arise from an unconventional symmetry-driven mechanism. Herein, we study the structural, electronic, and optical properties of altermagnet MnBr₂. The material has a rutile structure with lattice constants of a = b = 6.53315 Å, and c = 3.99758 Å. The antiferromagnetic state (AFM) was found to be more stable than the ferromagnetic state (FM) by calculating the energy difference between the FM and AFM states. To ensure thermodynamic stability, we calculated the formation energy, and the negative formation indicates that it is thermodynamically stable. We also calculated the phonon dispersion curve to ensure dynamic stability. The electronic band structure is calculated and found to exhibit the semiconducting nature of MnBr₂. We found the band splitting of 120 meV, indicating the altermagnet nature of MnBr₂. Furthermore, we investigated the optical parameters like the complex dielectric function, refractive index, absorption coefficient, reflectivity, and energy loss function in the energy range of 0–10 eV. Based on the obtained results, it can be suggested that MnBr₂ may be a potential candidate for spintronic applications.

The level of hydrogen peroxide (H₂O₂) in the human body is significantly associated with various pathological and physiological states, making it crucial to investigate its fluorescence sensing mechanism for synthesizing effective fluorescent probes. Herein, we used density functional theory and time-dependent density functional theory to investigate the fluorescence sensing mechanism of probe BTMFB for H₂O₂ detection. The theoretical results show that the fluorescence quenching mechanism of BTMFB is due to a non-radiative decay pathway dominated by the dark nπ* state. Subsequently, BTMFB reacts with H₂O₂ to form BTMB-OH, resulting in the turn-on fluorescence observed. The calculated potential energy curves indicate that BTFM-OH would undergo the ESIPT process under photoexcitation. The turn-on fluorescence is attributed to a local excitation mode for the bright ππ* state of the BTFM-OH-Keto. The reason for the high selectivity and rapid response speed of BTMFB for the detection of H₂O₂ is also explained by the calculated binding energy and reaction barrier, respectively.

Graphene nanoribbons (GNRs) have recently accumulated attention as alternative 2D semiconductors due to their remarkable electronic properties. The topological and entropy properties of graphene nanoribbons are very important to fully understand their electronic properties. Graphene nanoribbons with zigzag-shaped edges are narrow strips of graphene characterized by edges that form a zigzag pattern. In this study, we have obtained the analytical expressions for degree-based topological indices to uncover the structural properties of graphene nanoribbons composed of nanographene units with zigzag-shaped edges. Furthermore, we demonstrate the usefulness of different variations of hybrid arithmetic, geometric, harmonic, and Zagreb degree-based topological and entropy indices for these wavy zigzag nanoribbons.

Trifluoromethanesulfonyl fluoride (CF₃SO₂F) has attracted great interest as a promising replacement gas for sulfur hexafluoride in view of its excellent dielectric performance. The electronic structures of CF₃SO₂F and a total of seven dimeric complexes have been characterized theoretically using the M06-2X density functionals with the basis set up to 5-ζ (aug-cc-pV5Z + d) and Grimme's D3 dispersion corrections, the coupled-cluster with single, double, and non-iterative triple energies extrapolated to the complete basis set limit, and the symmetry-adapted perturbation theory (SAPT). The dimeric binding energies are in the range of 1–3 kcal mol⁻¹, depending strongly on the relative orientations of the monomers. The dominant dimerization occurs via the concerted interactions between CF₃ and SO₂ groups. A classical all-atom force field has been developed successfully for CF₃SO₂F on the basis of the SAPT-calculated decomposition asymptotes of the dimeric complexes. The vapor–liquid coexistence equilibria have been predicted using the hybrid Gibbs ensemble Monte Carlo algorithm. Theoretical vapor pressures and boiling point of CF₃SO₂F are in good agreement with the latest experimental data. In comparison with perfluoronitrile, CF₃SO₂F is superior in terms of liquefaction temperature but inferior in both viscosity and thermal conductivity. The present work sheds new light on the use of CF₃SO₂F as a promising alternative to dielectric and refrigerant fluids.

Computationally cost-effective methods with high accuracy are indispensable in the field of quantum chemistry. Recently, descriptor-based tuning methods of range-separated (RS) functionals have attracted theoreticians because of their improved performance in computing various chemical properties. In this article, we have assessed the performance of our newly developed electron localization function (ELF) tuned [J. Comput. Chem. 2017, 38, 2258] and solvent (Sol) tuned [J. Comput. Chem. 2020, 41, 295] RS functionals in the calculation of lowest singlet vertical excitation energies of a large set of molecules in gas and solvent continuum. Moreover, EOM-CCSD benchmark values of excitation energies have been generated in gas and solvents. Notably, the benchmark values under the influence of the solvent continuum have been computed using perturbation theory and density approach (PTED) to take care of solvent effects in EOM-CCSD calculations. This study envisages that our ELF and Sol-tuned functionals can accurately reproduce EOM-CCSD benchmark values. Furthermore, our Sol-tuned functionals can predict the decrease of excitation energies with solvent polarity, which is consistent with EOM-CCSD results.

Computational chemistry leverages computer simulation programs and theoretical models to anticipate molecular behavior, reactivity, and fascinating properties of metal complexes. In the current study, previously synthesized piroxicam complexes with Co, La, and Pr were investigated by employing and comparing three different functionals. Geometry optimization in gas and solvent, charge distribution and frontier molecular orbital (FMO), reactivity, stability, and Gibbs free energy in solution were investigated for the respective complexes calculated by employing B3LYP, M06, and M06l functionals through the Gaussian 9. The natural population analysis (NPA) revealed metal to ligand electron back-donation where the electrophilic active site primarily resides around the nitrogen and oxygen of the sulphonyl group, as affirmed by molecular electrostatic potential (MEP) diagrams. The global reactivity descriptors were analyzed by the computation of FMOs energies. The complexes were found to be stable, validated by large band gap energy, and relatively nonpolar in nature, which endowed them with the lipophilicity to permeate across biological membranes, corroborated by OSIRIS property analyzed through DATA WARRIOR 6. The theoretical calculations concluded that the studied complexes possess a high drug likeness score, an effective lipophilicity value, and biologically active characteristics with no side effects like tumorigenicity, mutagenicity, and irritability. Moreover, the biological interactions endured by metal complexes in the light of current speculative analysis have also been manipulated, crucial for the rational drug design.

Asphalt is composed of four main components, with over 50 different molecules identified to characterize asphaltenes, resins, aromatics, and saturates. However, there has been a lack of sufficient quantitative demonstration to determine the rationality of these molecules representing their respective components. In this investigation, 64 types of molecules representing the four components of asphalt were collected to develop a more realistic molecular model. Quantum chemical calculations were performed to determine the Mayer bond order, HOMO–LUMO gap, molecular mass, sp² hybrid carbon atom proportion, atomic charge, electrostatic potential, dipole moment, and molecular polarity index of the asphalt four-component molecules. Based on the statistical analysis of the aforementioned indicators, the rationality of the classification was demonstrated, and appropriate adjustments were made. The results indicated that saturates could be classified by Mayer bond order; Asphaltenes could be classified by the HOMO–LUMO gap and molecular mass; Resins and aromatics could be classified by molecular polarity index, average Mayer bond order, and sp² hybrid carbon atom proportion. This investigation provided a feasible method for classifying the four components of asphalt at the nanoscale and was expected to provide theoretical guidance for multi-scale investigation on asphalt performance.

The structures and properties of PtAg_n (n = 1–16) clusters have been studied by density functional theory (DFT). The Tpssh/def2-TZVP method is chosen in this work. Calculations reveal that the structures of PtAg_n (n = 1–16) clusters are planar structures when n = 1–3, while they present three-dimensional structures when n = 4–16. The coordination number of the Pt atom in PtAg_n (n = 1–16) clusters are in the range of 1–11. Pt atoms in PtAg_n (n = 1–16) clusters prefer to locate in the centers of the structures. The electronic structures are compared with available experimental and theoretical data. The stability analysis manifests that the clusters have odd-even stability properties. The study of catalytic properties on PtAg_n (n = 1–16) clusters perform similar interactions with one CO molecule. The Pt atom favors interacting with the carbon terminal of the CO molecule. According to the thermodynamic property study, the adsorption reactions of PtAg_n (n = 1–16) and CO are all spontaneous. The stability of PtAg_nCO (n = 1–16) clusters present odd-even properties. The projected density of states (PDOS) study reveals that the orbital hybridization phenomenon is present between the Pt and C atoms in the PtAg₆CO cluster.