International Journal of Quantum Chemistry最新文献

Structures, energetics and chemical bonding in molecular and ionic complexes of diatomic halogens and interhalogens XX′ (X, X′ = Cl, Br, I) with hexamethylenetetramine (HMTA) were computationally studied at the M06-2X/def2-TZVP level of theory. The stability of the molecular HMTA·nXX′ complexes decreases with increasing n: 1 > 2 > 3 > 4 for all XX′. The bonding between HMTA and XX′ in molecular complexes is best described as donor–acceptor interaction. Complexes with interhalogens, in particular with ICl, feature stronger donor–acceptor interactions and their dissociation is predicted to be endergonic at room temperature. In contrast, the intermolecular interactions are predominantly van der Waals type or electrostatic. Intermolecular N…X interactions are too weak for building coordination polymers based on HMTA and molecular halogens.

We investigate the structural, elastic, and thermodynamic properties of spinel compounds MgSc₂X₄ (X = S, Se) under high pressure using first-principles calculations. The obtained equilibrium structures at zero pressure show good agreement with previous theoretical and experimental results. The elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, B/G ratio, sound velocity, and Debye temperature were calculated under zero pressure and high pressure conditions. The B/G ratio reveals that both materials exhibit ductility under high pressure. Based on the Born stability criteria for cubic crystals under pressure, MgSc₂S₄ and MgSc₂Se₄ demonstrate structural stability within the investigated pressure ranges (up to 14.5 GPa for MgSc₂S₄ and 11.5 GPa for MgSc₂Se₄), and are predicted to lose stability at 33.43 and 25.81 GPa, respectively. Calculated anisotropy factors indicate elastic anisotropy in these compounds. Furthermore, thermodynamic properties of MgSc₂X₄ (X = S, Se) under high temperature and pressure were investigated through the quasi-harmonic Debye model. This study provides theoretical foundations for potential high-pressure applications of MgSc₂X₄ (X = S, Se).

A global potential energy surface (PES) for the CH₂(1¹A′) was constructed using neural network method based on high-level ab initio points. The topographic features of the PES were discussed and compared with available theoretical and experimental values. The results indicate that the present PES is accurate and reliable. To further clarify the reality of the PES, the dynamics calculations of the C(¹D) + H₂ → H + CH(X²Π) reaction were performed using time-dependent wave packet method. Some meaningful dynamic results including reaction probability, integral cross section, differential cross section, and rate constant were calculated and compared with previous theoretical and experimental values. The reasonable dynamics results indicate that the present PES can be used to perform any kind of dynamics studies.

Based on the newly reported nonadiabatic potential energy surfaces, comprehensive adiabatic and nonadiabatic dynamical calculations for the S⁺ + HD reaction were carried out within the collision energy range of 1.0–4.0 eV. To quantitatively evaluate the nonadiabatic effects, a systematic comparison was conducted between the adiabatic and nonadiabatic dynamical results. The analysis demonstrates that the nonadiabatic effect induces negligible variation on the reaction probabilities and total integral cross sections. However, significant nonadiabatic influences were observed in the vibrational-rotational state distributions of products. The differential cross section analysis unveiled a distinct reaction mechanism. The SH⁺ + D channel exhibited a strongly forward-peaked angular distribution, indicating predominant direct abstraction dynamics through collinear attack geometry. In contrast, the SD⁺ + H channel shows a prominent backward-scattering component, attributed to impulsive rebound dynamics characterized by hard-sphere collisions.

To elucidate the pressure dependence of orthorhombic Mo₂BC properties, this study employs density functional theory (DFT) to investigate its mechanical, electronic, lattice dynamic, and thermal behavior. The obtained lattice parameters and elastic properties of Mo₂BC exhibit strong agreement with existing theoretical findings. The band structure calculations reveal that orthorhombic Mo₂BC maintains metallic behavior under pressures spanning 0–50 GPa. Mo₂BC demonstrates mechanical (Born stability criteria) and dynamic stability up to 50 GPa, with elastic constants and moduli exhibiting a monotonic increase with applied pressure. Notably, pressure induces a brittle-to-ductile transition in Mo₂BC within the 10–50 GPa. In-plane profiles of linear compressibility, shear modulus, and Young's modulus coupled with surface structural analyses highlight that anisotropy intensifies with increasing pressure. Furthermore, thermal properties (Gibbs free energy [F], internal energy [E], entropy [S], and heat capacity [C_V]) under combined high-temperature and high-pressure conditions were systematically investigated.

B3LYP and M06-L density functional calculations have been performed to evaluate the binding phenomena of the Fe(II), Co(II), Ni(II), and Cu(II) ions with the biologically important mandelic acid (MA) ligand in the gas phase and in the aqueous PCM model. The influence of the metal nature, spin states, coordination mode, chelate effects, and ring strain was explored. The direct interactions of the Fe(II), Co(II), Ni(II), and Cu(II) ions with the deprotonated MA⁻ ligand resulted in the stabilization of twenty-eight stable mandelate complexes. A similar chemical reactivity was observed for the Fe(II), Co(II), and Ni(II) ions towards the MA⁻ form, with the highest ΔE_Bond values calculated for the Cu(II) complexes. The AIM, FMO, and NBO results indicate that the nature of all MO chemical bonds is partly ionic and covalent, with a medium strength bond. The IR and UV-Vis absorption spectra of MA⁻ and mandelate complexes were calculated and compared to experimental spectra. The UV-Vis absorption bands of mandelate complexes involve metal-to-ligand charge transfer through d-π* electron transitions, particularly with relatively high intensities in the visible region of the spectrum for the five-coordinated Cu(II) complexes.

The fluorophore 2-butyl-4-hydroxyisoindoline-1,3-dione (BHD) has been obtained experimentally (RSC Adv., 2015, 5, 18177–18182). However, the influence of protic solvent and intermolecular hydrogen bond (InterHB) between BHD and solvent has not been considered. On this foundation, we systematically explored the effect of protic water on the ESIPT mechanism of BHD adopting density functional theory (DFT) and time-dependent DFT (TD-DFT). From a series of data, it can be ensured that the intramolecular hydrogen bonds (IntraHBs) and InterHBs in BHD and its hydrogen-bonded complexes (BHDH₂O, BHD(H₂O)_cyc) are enhanced upon photoexcitation. For BHD, BHDH₂O and BHD(H₂O)_cyc, the proton transfer process can only occur in the excited state. The potential barriers of ESIPT in BHD and BHDH₂O are 2.6362 and 3.8611 kcal/mol, respectively. Clearly, the extra InterHB that does not involve in the proton transfer reaction hinders the ESIPT process in BHDH₂O. For the cyclic hydrogen-bonded complex BHD(H₂O)_cyc, excited state double proton transfer (ESDPT) process occurs in a concerted but asynchronous protolysis pattern, requiring only conquering a potential barrier of 0.0356 kcal/mol, as shown in the potential energy curve. Compared with BHD, the two InterHBs in BHD(H₂O)_cyc obviously reduce the potential barrier and effectively accelerate the ESPT process.

Atomic basis sets play a central role in molecular chemistry and computational studies. While numerous large and specialized basis sets have been developed, the minimal STO-3G basis set continues to be used. It is commonly employed in the testing phase of calculations, for determining magnetic properties of larger systems, and for describing chemical environments in multilayer QM/QM' calculations focused on extended biological or material systems. The original STO-3G basis set was optimized to fit a single atomic Slater-type orbital, with no emphasis on energy or properties. In this study, we explore the possibilities, advantages, and drawbacks of re-optimizing the STO-3G basis set in the following ways: (i) targeting the total energy of different organic molecules rather than atoms during the optimization process; (ii) introducing different basis set “atom types” for the same atom, inspired by force fields; (iii) optimizing the basis set to improve equilibrium geometries and/or electric properties.

Heterocyclic compounds containing thiazolo and pyrimidine rings have attracted significant interest due to their diverse biological activities and structural versatility. The fusion of thiazole with pyrimidine or pyridine frameworks enhances their pharmacological potential and electronic stability. This work aimed to synthesize new heterocyclic derivatives based on benzylidene-thiazolidin-4-one scaffolds and evaluate their electronic, structural, and biological characteristics using both experimental and computational approaches. Benzylidene-thiazolidin-4-one derivatives 1 and 2 were condensed with guanidine hydrochloride to afford thiazolo[4,5-d]pyrimidin-5-amine and methyl benzoate 4. Subsequent reactions with malononitrile yielded thiazolo[4,5-d]pyrimidin-5(6H)-thione (5) and thiazolo[4,5-b]pyridine-6-carbonitrile 6. Density Functional Theory (DFT) calculations were performed to predict the molecular geometry, dipole moments, bond angles, bond lengths, and electronic properties. Reactivity and stability were evaluated from the HOMO–LUMO energy gap. Molecular docking studies were conducted to assess binding affinity with antibacterial and antimalarial protein targets. DFT analysis indicated that compound 3 exhibited the highest softness (σ = 16.129 au), whereas compound 6 behaved as a hard compound (σ = 18.519 au). HOMO electron density in compounds 3 and 5 was mainly localized on the NO₂ group (98.4–100%), while in compounds 4 and 6, it was delocalized across the dihydrothiazolo and aromatic rings. Excited states of compound (3) were assigned to π–π* transitions (λ = 208.09–223.42 nm) and n–π* transitions (λ = 255.38–324.46 nm). Molecular docking revealed strong ligand–protein interactions, including four conventional hydrogen bonds, confirming high stability and binding affinity toward antibacterial and antimalarial targets. The synthesized thiazolo[4,5-d] and thiazolo[4,5-b] derivatives demonstrated favorable electronic properties and strong protein binding affinities, suggesting their potential as promising scaffolds for antimicrobial and antimalarial drug development.

In this study, we achieve polarization and temperature-insensitive triple plasmon-induced transparency (triple-PIT) at terahertz frequencies using a novel graphene metamaterial comprising a graphene block, four graphene squares, and four graphene strips. The insensitivity of this structure to changes in the incident light's polarization angle is attributed to its high symmetry. The expressions of nth-order coupled mode theory are derived accurately, and its theoretical predictions closely align with the findings of numerical finite-difference time-domain simulations for a triple-PIT system with n = 4. Our results reveal that two synergistic single-PIT phenomena lead to a distinct and tunable triple-PIT effect in the designed metamaterial. This observation is further validated through field distribution studies. Additionally, given the continuous nature of graphene used in the metamaterial, its Fermi level and carrier mobility are easily and dynamically tunable under an applied voltage bias. Notably, the group index of the designed triple-PIT system varies between 603 and 817 as graphene's Fermi level rises from 0.8 to 1.2 eV. In contrast, the group index ranges between 778 and 1216 as graphene's carrier mobility increases from 2.5 to 4.5 m²/(V s). Moreover, the maximum group index reaches 1216 at 4.5 m²/(V s), demonstrating the potential of the system in slow-light applications. Thus, the proposed patterned graphene metamaterial and its related findings provide valuable insights for advancing optical switches, dynamically tunable modulators, multichannel filters, and high-performance slow-light devices.