International Journal of Quantum Chemistry最新文献

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.

This work presents a quantum mechanical charge field molecular dynamics (QMCF MD) simulation study exploring the structural and dynamic properties of hydrated Y³⁺ ions in an aqueous solution. The simulation results reveal the formation of two hydration shells over a simulation time of 180 ps. The first hydration shell predominantly consists of eight water molecules, with a lower probability of nine, indicating a flexible hydration structure. A total of 84 successful ligand exchange events were recorded during the simulation. The mean residence times of the water molecules in the first and second hydration shells were 18.0 and 2.27 ps, respectively. The square antiprism geometry was adopted for the octahydrate, whereas the gyroelongated square antiprism geometry was adopted for the nonahydrate. The vibrational stretching frequency of Y³⁺O bonds was determined to be 352 cm⁻¹, consistent with the experimental values of 384 and 379 cm⁻¹ of hydrated yttrium perchlorate and yttrium nitrate. These findings indicate that the QMCF MD simulations can effectively describe the hydration structure and dynamics of Y³⁺, providing valuable insights into the behavior of this rare earth ion in aqueous environments and complementing experimental studies of hydrated Y³⁺.

Herein, the structural features, mechanical stability, electronic response, optical properties, and thermoelectric aspects of Li₂YAuX₆ (X = Br or I) are examined via first-principles computations. The Born-Huang criterion, formation energy, and tolerance factor ensure the mechanical, thermal, and structural stabilities. Several elastic characteristics have been obtained, including elastic constants, moduli, ductility, wave velocities, Debye temperature, and melting points. The data on elastic features indicate that Li₂YAuBr₆ and Li₂YAuI₆ possess ductility and sufficient flexibility to be employed in flexible solar devices. Moreover, the estimated band gap values for Li₂YAuBr₆ and Li₂YAuI₆ are 2.65 and 2.15 eV, respectively. The obtained band structures demonstrate the semiconducting nature with indirect band gaps. The density of states has been ascertained to determine the contributing states in electronic transitions. The optical features have been calculated to evaluate the response of both materials to incoming light photons. Li₂YAuBr₆ is effective at photon absorption over the ultraviolet (UV) spectrum, whereas Li₂YAuI₆ demonstrates visible and UV light absorption, making them suitable for photovoltaics. Thermoelectric aspects have been calculated to analyze the performance of materials for deployment in wasted heat conversion technologies. The minimum heat conduction and increased power factor lead to considerable ZT values of 0.79 and 0.81. These findings suggest that these materials have great promise for application in photovoltaic and thermoelectric systems.

This study addresses the global rise in energy demand and the environmental challenges posed by fossil fuel usage, such as greenhouse gas emissions and pollution. It explores the potential of cluster catalysts, specifically gallium (Ga) and beryllium (Be) clusters, for splitting water molecules to generate hydrogen. Using density functional theory (DFT), we conducted an in-depth analysis of the interactions between Ga₅ and Ga₄Be clusters with water molecules and the mechanisms of hydrogen production. The results indicate that while Be doping slightly reduces the binding energy and structural stability of the clusters, it significantly decreases the band gap, promoting electron transfer and enhancing catalytic activity. Adsorption energy calculations reveal that Be doping notably increases the adsorption strength of water molecules on the cluster surface, particularly through the formation of Be-O chemical bonds. This enhanced adsorption effect facilitates the breaking of O-H bonds in water molecules, significantly lowering the reaction energy barrier and transforming the process from an energy-driven to a spontaneous exothermic reaction. Furthermore, the resulting hydrogen molecules are adsorbed on the cluster surface through van der Waals forces, making them easy to desorb. This indicates that the catalytic system is highly efficient in hydrogen production and holds strong potential for practical applications.

An accurate expression of the kinetic energy density of an electronic distribution in terms of the single-particle reduced density matrix for atomic and molecular systems is a long-standing problem in electron structure theory. Existing kinetic energy density functionals are generally expressed as modifications over kinetic energy of homogeneous electron gas and/or von Weizsäcker kinetic energy. A large class of these functionals also requires empirical parametrizations to make accurate predictions of the kinetic energy for atomic and molecular systems restricting their transferability. Moreover, the correct kinetic energy density which produces accurate local properties such as atomic shell structure is still an unsolved problem. In this work, we have developed an exact methodology that can be used to derive the kinetic energy of an electronic system of arbitrary spin multiplicity. One of the attractive features of this present analytical formalism is the possibility of systematic improvement of the kinetic energy by virtue of a novel perturbation series. Applying this methodology to simple model systems such as one-dimensional quantum harmonic oscillator and homogeneous electron gas produces a qualitatively correct $��N�$-dependence of kinetic energy as a result. A one-to-one correspondence between our formalism to the traditional Green's function formalism is also demonstrated.

To improve the overall properties of YB₁₂ ceramics, the influence of refractory metals on the structural stability, Vicker hardness, elastic properties, elastic anisotropy, and thermodynamic properties of YB₁₂ boride is studied using first-principles calculations. The result shows that the structural stability of TM-doped YB₁₂ becomes better with decreasing the valence electronic density for these refractory metals. In particular, the calculated Vickers hardness of Re-doped YB₁₂ is 40.2 GPa, which is higher than that of YB₁₂ (36.21 GPa) and the other TM-doped YB₁₂. The high hardness of TM-doped YB₁₂ is demonstrated by the change of Poisson ratio (δ) and B/G ratio. Naturally, the high hardness of Re-doped YB₁₂ is that the refractory metal enhances the localized hybridization between B and B atoms in B₁₂ cage, which is demonstrated by the change of the B–B covalent bond. In addition, YB₁₂ and TM-doped YB₁₂ borides exhibit elastic isotropy. Finally, it is found that these refractory metals (except for Re) enhance the melting point of YB₁₂.

We present how to use web technologies to generate a cross-platform GUI. Specifically, we use Electron to build a cross-platform desktop application with JavaScript, HTML, and CSS for the PyBEST quantum chemistry package. The interface offers easy access to PyBEST's methods, including Hartree-Fock (HF), Second-order Møller-Plesset perturbation (MP2), pair Coupled Cluster Doubles (pCCD), various Coupled Cluster (CC) ansätze, and Equation of Motion (EOM) approaches. Key features include molecular geometry input, Hamiltonian configuration, and method-specific settings through a tab-based interface. The GUI simplifies input generation and provides built-in validation to prevent common user errors. This development significantly reduces the learning curve for quantum chemistry software, enabling researchers to focus on scientific research rather than technical setup.