International Journal of Quantum Chemistry最新文献

In this study, a series of novel chromophores featuring pyrazinoquinoxaline (PQ)-type variant conjugated bridges and powerful push-pull effects was designed and systematically investigated. These PQ chromophores possess unique ladder-type D-π_D-A, D-π_A-π_D-A, and D-π_A-A configurations, first proposed and explored in the nonlinear optical (NLO) field. A comprehensive investigation of core properties, including aromaticity, static hyperpolarizability, dipole moments, excited-state properties, stability, 2D second-order nonlinear response spectra, and structure–property relationships was conducted through multiple advanced analytical methodologies. The structure of PQ conjugated bridges, acceptor strength, and dielectric surrounding were found to exert significant impacts on the hyperpolarizabilities and dipole moments of new PQ chromophores. Intriguingly, in contrast to traditional polyene-bridged chromophores, PQ-type systems exhibit a V-shaped hyperpolarizability curve with increasing pyrazine rings on the conjugated bridge, accompanied by enhanced transition dipole moment squared, elevated polarity, a sharp decline in HOMO energy levels, and diminished aromaticity. The crucial states governing hyperpolarizability in PQ-type chromophores are S₃ or S₄ state. The number of pyrazine rings on the PQ-type bridge determines the key factors influencing hyperpolarizability. DN-PQ0-AS1 and DN-PQ6-AS1 exhibit remarkable hyperpolarizabilities and dipole moments in chloroform and acetonitrile, resulting in outstanding molecular hyperpolarizabilities. Significantly, DN-PQ6-AS1 and DN-PQ5-AS1 exhibit ultra-deep HOMO energy levels of −8.26 eV and −8.16 eV respectively, indicating that these chromophores possess exceptional oxidation resistance, chemical stability, and air stability. This directly solves the urgent problem of insufficient stability in the processing and polarization of NLO materials. The unique D-π_A-π_D-A, D-π_D-A, and D-π_A-A configurations in this system contain donor-acceptor pairs with various lengths and strengths, resulting in multilevel and multiscale characteristics of electronic transitions and charge transfers. These structural features critically influence hyperpolarizability density and 2D NLO responses. Several PQ chromophores exhibit excellent EOPE/OR performance (exceeding 1 × 10⁻²² esu). Notably, DN-PQ4-AS1 shows exceptional SHG response values (1.902 × 10⁻²³ esu). This mechanistic understanding of novel PQ conjugate systems provides innovative design strategies for developing multifunctional high-performance NLO materials.

A theoretical investigation at MP2 = full/aug-cc-pVTZ level has been carried out on the hydrogen and halogen bonded complexes of the HOCl molecule with various Lewis bases (N-, S-, and O-bases), aiming to identify a suitable descriptor for evaluating the bond strength in a generalized manner. A total of 24 halogen and hydrogen bonded complexes formed between the HOCl molecule and different electron donors have been investigated. The binding strength of these complexes was analyzed in relation to several descriptors, including proton affinity (PA), negative electrostatic potential (V_s,min), electron density ρ(r_c) at the bond critical point (BCP), charge transfer (CT), and hyperconjugation energy. Among these, the electron density emerged as the most reliable descriptor, showing a strong correlation with the binding strength across all the studied complexes, followed by hyperconjugation energy. In contrast, other parameters exhibited good correlations only when evaluated for specific bases but failed to maintain consistency across all types of complexes. These correlations not only contribute to a better understanding of the nature of hydrogen and halogen bonds with the HOCl molecule but also offer an effective approach for predicting their relative strengths, particularly in scenarios where both types of interactions coexist and compete with each other.

Small-molecule non-fullerene acceptors (SM-NFAs) featuring a three-dimensional and four-bladed propeller-like structure have gained attention due to their unique molecular framework as a guest component in ternary organic solar cells (TOSCs). However, there is currently a scarcity of theoretical research into the photovoltaic properties of these SM-NFAs. This gap is especially pronounced when it comes to comprehending how modifications to their end groups (EGs) influence their electronic structures. In this work, SF-BTA1, SF-BTA2, and SF-BTA3 SM-NFAs are selected since they have been experimentally synthesized and have different impacts on the performance of TOSCs. Using density functional theory (DFT) and time-dependent DFT (TDDFT), we have computed and analyzed their ground state and excited state properties, including molecular planarity, electrostatic potential maps and their corresponding fluctuations, dipole moments, frontier molecular orbitals, electron–hole distributions, UV–Vis absorption spectra, singlet-triplet energy gap difference (∆E_ST), and exciton binding energy, as well as the open-circuit voltage of OSCs based on these four-bladed propeller-like molecules. The theoretical results align well with experimental data. Furthermore, as a guest acceptor, SF-BTA1 exhibits the smallest electrostatic potential fluctuations and singlet-triplet energy gap (∆E_ST). This implies that these two factors could play crucial roles in evaluating whether a four-bladed propeller-like molecule is suitable to serve as an effective guest acceptor. Our results not only unveil the underlying mechanism about the roles of these NFAs in TOSCs but also provide valuable insights for the further design and optimization of highly efficient TOSCs.

The structure and UV/Vis-absorption spectra of Li₂S_n (n = 2–8) in sulfolane solution (Sl), as well as the thermodynamic parameters of their com- and disproportionation, have been studied using DFT to gain a deeper understanding of the nontrivial mechanistic steps underlying the S-shaped discharge voltage curve of the Li-S electrochemical system. Comproportionation of Li₂S_n was established using PBE0/6–311 + G(d,p) approximation with PCM to be thermodynamically favorable: the greater the difference in the oxidation states of the interacting forms, the more significant the Gibbs free energy drop. The transformations of Li₂S₃ and Li₂S₆ drop out of the general pattern: dis- and comproportionation for them are allowed equally, which can lead to a smooth change in the concentrations of Li₂S₈, Li₂S₄, and Li₂S₂ and, thus, provide a relatively constant potential in the low-voltage part of the Li-S battery discharge curve. UV/Vis-absorption spectra of Li₂S_n obtained using TD-DFT [TPSS/6–311 + G(d,p)] with PCM + explicit solvation were found to present allowed electronic transitions located from 30 000 to 50 000 cm⁻¹. It has also been observed that Li₂S_n self-association in Sl is relevant mainly for short-chain structures (n = 2–4); there is a dynamic equilibrium between different forms of Li₂S_n, and the solution is usually presented by a mixture of these forms.

Propylene oxide (PO) is a crucial chemical intermediate, but its conventional production methods come with several limitations. In contrast, the propylene gas phase epoxidation process has garnered significant interest due to its environmentally friendly approach, utilizing cost-effective and readily available raw materials and producing water as the sole byproduct. This study employs density functional theory to systematically explore catalytic propylene epoxidation on the Ag(100) surface. By systematically examining the effect of varying oxygen coverages on the Ag(100) surface, the research determines the saturation oxygen coverage through successive oxygen atom adsorption. Furthermore, it assesses the propylene epoxidation reaction at different oxygen coverage levels on the same surface. During this process, two parallel reaction pathways are studied: α-H-stripping to produce acrolein and the formation of a metal-epoxide intermediate (OMMP2) through epoxidation, which further produces PO and acetone (AC). For the primary competitive reaction, a lower oxygen coverage favors the first step of α-H abstraction, while the opposite is true for the epoxidation process; for the secondary competitive reaction, increasing the oxygen coverage favors the formation of PO and AC. The findings reveal that oxygen exposure substantially affects the primary competitive response and also exerts a considerable influence on the secondary competitive process. The second α-H abstraction to produce acrolein requires higher activation energy compared to the secondary competitive reaction producing PO, thus making PO more likely to be formed than acrolein as the oxygen coverage increases.

Using the time-dependent wave packet method, the reaction channels of Si(¹D) + H₂(X¹Σ_g⁺) (v₀ = 0–4, j₀ = 0–8) → H(²S) + SiH(X²П) were investigated on an accurate global potential energy surface of SiH₂(1²A′) in the collision energy range of 0.1–2.1 eV. Quantum dynamics calculations reveal interesting features of detailed dynamical quantities and underlying new mechanisms. The collision energy dependence and integral scattering cross-section of reaction probabilities with different total angular momenta are discussed in detail. The thermal rate constants of H₂ molecules under vibrational excitation and rotational excitation were analyzed. It was revealed that the vibrational excitation dominated the reactant activity; however, rotational excitation had a weak effect on the reaction due to the late barrier.

2,2-Diphenyl-1-picrylhydrazyl radical (DPPH^•) is widely used as a stable free radical for estimating radical scavenging activity of antioxidants. DPPH⁺ is an oxidized form and DPPH⁻ is a reduced form of DPPH^•. 2,2-Diphenyl-1-picrylhydrazine (DPPH-H) is a neutralized form of DPPH^•. In this study for the first time, the bonding and electronic characteristics of these molecules are directly compared using density functional theory calculations including dispersion corrections (DFT + Disp). The natural bond orbital (NBO) and electron localization function (ELF) analyses are performed to characterize the bonding and nonbonding orbitals and to describe the best resonance structure for these molecules. The canonical molecular orbital (CMO) analysis is used to determine the bonding nature of molecular orbitals involved in electronic transitions. It is found that the nonbonding orbitals of nitrogen atoms play the leading role in delocalization effects. The odd electron of the nitrogen atom in DPPH^• is engaged in the formation of the CN and NN π-bonds, which stabilize DPPH^• considerably. The molecular orbital (MO) and density of states (DOS) diagrams show that the energy gap of DPPH^• increases by losing an electron to form DPPH⁺ or accepting an electron to form DPPH⁻ or upon hydrogen atom abstraction to form DPPH-H. The time-dependent density functional theory (TD-DFT) calculated ultraviolet–visible (UV–Vis) absorption spectrum of DPPH^• shows two distinct bands in both ultraviolet and visible regions, while the other molecules have only a unique absorption band. A good agreement between the calculated data and the earlier experimental observations is obtained.

Metal–ligand interactions, particularly those involving noble metals, have not been extensively studied using energy decomposition analysis frameworks. Noble metals—Pyridine (Py) interactions are very interesting since this ligand has been used as a probe to sense metal nanoparticles' activity and optical properties. Understanding the nature of Cu, Ag, and Au interactions with Py is especially relevant for spectroscopic applications, such as Surface-Enhanced Raman Spectroscopy, where metal–ligand interactions play a critical role in signal enhancement and selectivity. This work uses a simple model of homometallic and heterometallic noble metal dimers in interaction with Py, and with supermolecular and SAPT schemes, we evaluate the strength of the XCu, XAg, and XAu–Py (XCu, Ag, Au) interactions. The potential energy surface across metal–Py distances was obtained using the PBE0, SAPT2+(CCD)δMP2, SAPT2+(CCD)δMP2 and SAPT2+(3)(CCD)δMP2 methods and was systematically compared against reference data obtained at the CCSD(T) level of theory. No single SAPT method universally reproduces the high-level CCSD(T) reference interaction energies across all metal–Py complexes analyzed. The bonding in XCu–Py complexes exhibits a predominantly electrostatic character, for which SAPT2+(CCD)δMP2 yields excellent agreement with CCSD(T) data. In contrast, accurate modeling of XAu–Py interactions requires an appropriate description of dispersion forces, making dispersion-inclusive SAPT variants: SAPT2+(3)δMP2, SAPT2+(3)(CCD)δMP2, essential. XAg–Py complexes exhibit intermediate behavior between the two extremes. The most stabilized metal–Py interactions correspond to those exhibiting the largest induction energy contributions. Furthermore, the extent of orbital overlaps at equilibrium structures may significantly influence overall stability.

Pesticides, biocides, and antiparasitic agents play a crucial role in protecting crops, public health, and livestock. Pesticides help control pests that damage crops, ensuring food security and higher agricultural yields. Biocides are essential for disinfecting surfaces, controlling harmful microbes, and preventing the spread of diseases in homes, hospitals, and industries. Antiparasitic agents are vital in veterinary and human medicine, treating and preventing infestations by parasites such as ticks, lice, and worms. Understanding the physicochemical properties of these drugs is essential for their effective application and safety assessment. In this study, we employ eigenvalue-based topological indices to estimate four key physicochemical properties—complexity, molecular weight, molar volume, and molar refractivity of 59 such drugs. A linear regression model is developed, where topological indices serve as independent variables and physicochemical properties as dependent variables. The results indicate that the Laplacian Estrada index is the most effective predictor of complexity ($��R^2�=�0.969�,�p�=�1.04�\times �{10}^{�-�44�}�$), while molecular weight is best estimated using the EA energy ($��R^2�=�0.946�,�p�=�6.72�\times �{10}^{�-�38�}�$). To validate our approach, we compare the predicted and actual values of molecular weight and complexity for Icaridin, Spinosyn A, and Spinosyn D, demonstrating high prediction accuracy. These findings highlight the potential of eigenvalue-based topological descriptors in computational drug characterization.

Due to the limitations of comprehensive experimental and theoretical research, rate coefficients are commonly derived through analogies with alcohols or estimations based on alkane data. Consequently, this paper delves into the critical H-abstraction reactions involving n-hexanol and radicals (Ḣ, HȮ₂, ȮH and ĊH₃), serving as foundational steps in the combustion mechanism. Rate coefficients are determined using traditional and variational transition state theory combined with Eckart tunneling correction. Emphasis on H-abstraction from C_α is evident in branching ratios for n-hexanol + Ḣ/HȮ₂/ĊH₃ systems, while the dominant reaction for n-hexanol + ȮH system shifts from C_ε above 330 K to C_β below 330 K. The total H-abstraction rate coefficient for n-hexanol + ȮH is calculated as k_OH = 12.76 × T^3.62 × exp. (472.81/T) (cm³mol⁻¹ s⁻¹), with the CBS-QB3 level reproducing experimental data commendably. Furthermore, the kinetics model proposed by Togbé et al. is refined through updated rate coefficients, validated against ignition delay times, showcasing notable agreement with experimental data. Reaction path and sensitivity analyses provide insights into crucial reactions and corresponding fuel consumption paths during n-hexanol oxidation.