International Journal of Quantum Chemistry最新文献

The unrestricted doubly occupied configuration interaction methods have enabled to describe satisfactorily $��N�$-electron systems, although they very often yield spin-contaminated wave functions. This contamination can partially be reduced by application of the half-projection technique [J. Garcia et al. J. Chem. Phys. 161, 224 112 (2024)]. In this work, we propose a new alternative treatment within the half-projection scheme, which leads to results in terms of potential energy curves and their corresponding $��\left({\hat{S}}^2\right)�$ expectation values in prototype strongly correlated $��N�$-electron systems. These results have been systematically compared with those obtained from previously reported treatments using half-projection techniques, with those of the ordinary unrestricted doubly occupied configuration interaction procedure, and with those arising from the full configuration interaction method. We show that the new proposed method allows for a further reduction in the spin contamination, while it does not require significant increases in computational costs.

Half-Heusler compounds are promising quantum materials for thermoelectric applications due to their excellent electronic properties, including semiconductivity, thermoelectricity and topological insulating behavior. However, optimizing their mechanical stability and optical phenomena remains a challenge. This study employs density functional theory (DFT) with the generalized gradient approximation (GGA-PBE) for the exchange-correlation functional to characterize the novel quaternary Half-Heusler alloys ANiSn_0.5M_0.5 (A = Zr, Ti; M = Si, Ge, Sb). The structural, electronic, thermodynamic, mechanical and optical properties were systematically analyzed. Although the compositions via fractional substitution are unexplored, this investigation reported a comparison analysis alongside prior articles on related samples. Surprisingly, structural analysis suggests that the samples exhibit a cubic to tetragonal transition, while elastic constants confirm that TiNiSn_0.5Si_0.5 and TiNiSn_0.5Sb_0.5 are highly mechanically stable materials. Moreover, Pugh's ratio of 2.01 (for TiNiSn_0.5Si_0.5) and 3.25 (for TiNiSn_0.5Sb_0.5), alongside Debye temperatures of 360.02 and 231.43 K, respectively, were obtained, indicating a ductile character and strong phonon scattering and potentially low lattice thermal conductivity. Electronic structure analysis shows that Sb doping introduces metallic behavior, while Si/Ge alloying maintains semiconducting character. Furthermore, optical behavior reveals higher absorption at the visible-lower UV regions, fluctuated reflectivity around 0.5 and a lower level of conductivity and dielectric constant. While fractional Sn-site substitution strategies have precedent in related half-Heusler families, the specific ANiSn_0.5M_0.5 compositions examined here, together with their combined electronic, mechanical, and optical characterization, have not been previously reported, and this investigation situates the results within the context of prior work on related compounds.

The structural, electronic, bonding, and optical properties of LiN_1−xP_xMg (x = 0, 0.25, 0.5, 0.75, and 1) half-Heusler alloys were investigated using density functional theory within the GGA and modified Becke–Johnson (mBJ) frameworks. Attention was given to the intermediate compositions (x = 0.25, 0.5, and 0.75), for which detailed theoretical data are not available in the literature. Structural optimization confirms the stability of all investigated compositions and shows that phosphorus substitution leads to a nonlinear expansion of the lattice together with a gradual reduction in stiffness. Among the studied alloys, the x = 0.5 composition exhibits the lowest equilibrium energy, indicating enhanced energetic stability. Electronic structure calculations reveal a clear composition-dependent evolution of the band gap, with direct-gap semiconducting behavior preserved up to x = 0.75 and a transition to an indirect band gap in LiPMg (x = 1). The mBJ calculations predict tunable band gaps ranging from 3.48 to 1.74 eV, highlighting the strong influence of alloying on the electronic properties. Bonding analyses based on COHP, charge transfer, and electron localization function calculations further show that replacing N with P modifies the bonding environment and promotes changes in electron distribution across the lattice. In addition, all compositions exhibit strong optical activity in the visible and ultraviolet regions, characterized by enhanced absorption, optical conductivity, and inter band transitions. These results demonstrate that phosphorus substitution offers an effective route for tailoring the electronic and optical response of LiN_1−xP_xMg alloys, making them promising candidates for future optoelectronic and photonic applications.

Organic solar cells based on donor–acceptor heterojunctions rely on interfacial charge transfer (CT) for exciton dissociation and charge transport. This study combines DFT, TD-DFT, and AIMD simulations to investigate the electronic structure and CT properties of PM6 donor dimers with PY-X non-fullerene acceptors (X = CH₃, OCH₃, CN, COCH₃, NH₂, NHCH₃), using PM6:PY-CH₃ as the reference. Three substituted derivatives are highlighted: PY-CN and PY-COCH₃ exhibit strong CT character (∼54%–51%), low band gaps (∼2.0 eV), and deep LUMO levels favoring electron transfer, while PY-NHCH₃ offers a high open-circuit voltage (1.76 eV) and fill factor (92%) despite weak CT (∼6.6%). Notably, after AIMD simulations in explicit chloroform, the most optically active excited state of the PM6:PY-CN dimer exhibits a high CT character (∼56.56%), together with the smallest band gap indicating highly efficient exciton dissociation. AIMD simulations in chloroform reveal that solvent-induced structural relaxation enhances CT interactions and stabilizes the donor–acceptor interface. Overall, substituent effects, solvent interfacial interactions, and π–π stacking are key modulators of exciton dissociation and charge transport, offering design guidelines for high-performance, stable organic solar cells.

Three-dimensional materials exhibiting through-space charge transfer (TSCT) have garnered extensive research interest in the field of nonlinear optics (NLO). In this work, density functional theory (DFT) was employed to systematically investigate a series of donor (D)-carbazole-acceptor (A) type compounds (1–6) and traditional D–A type compounds 7 and 8. Their geometric structures, absorption spectra, charge transfer characteristics, and second-order NLO properties were analyzed, with emphasis on clarifying the influences of D/A types and substitution positions on the first hyperpolarizability (β_tot) and charge transfer (CT) processes. The results reveal that replacing the acceptor unit from phthalimide (compound 6) to dibenzo[a,c]phenazine (compound 3) results in a 3.86-fold enhancement in the β_tot value, whereas variations in the donor moiety or substitution position exert relatively weaker effects. This demonstrates that the D-carbazole-A skeleton is highly sensitive to acceptor modifications and plays a dominant role in modulating the second-order NLO properties. Notably, the β_tot value of compound 6 (2.2 × 10⁻³⁰ esu) is significantly lower, which can be attributed to its unique orbital contributions (HOMO → LUMO + 1), distinct TSCT character, and smaller oscillator strength of the main excited state. In summary, the types and positions of substituents and the CT mode can effectively modulate the second-order NLO response, providing new strategies for the design of novel NLO materials.

The influence of the superbase nature on the reaction mechanism of the methanol isopropenylation with a propyne-allene mixture in the KOH·0.5H₂O/NMP and KOH/DMSO systems has been studied using a combined quantum chemical approach including DFT methods (B2PLYP-D2/6–311+G**//B3LYP/6–31+G* + PCM). The superbases are modeled by the pentasolvate complexes KOH·5NMP, KOH·H₂O·5NMP and KOH·5DMSO. According to the results obtained, the reaction proceeds preferentially via the addition of methoxide ion to allene, and this is the rate-determining stage. A significant decrease in the yield of the reaction product in the KOH·0.5H₂O/NMP system (KOH·H₂O·5NMP complex) compared to KOH/DMSO (KOH·5DMSO complex) is explained by a higher activation barrier associated with the hydration of the attacking nucleophile. The lower activation barrier of the rate-determining stage obtained in the presence of KOH·5NMP, compared to KOH·5DMSO, shows the competitiveness of the KOH/NMP system over KOH/DMSO in the vinylation of alcohols by propyne-allene mixture under anhydrous conditions.

Using first-principles DFT, we investigate the synergistic modulation of the electronic structure of monolayer MoSe₂ by biaxial strain and Frenkel defects for electrocatalytic hydrogen evolution. A biaxial compressive strain of −4% lowers the Frenkel defect formation energy from 2.41 eV to 1.85 eV. The defect-strain synergy introduces in-gap states, increases the density of states at the Fermi level, modulates the Mo d-band center, strengthens orbital hybridization, and optimizes surface charge distribution and work function. Consequently, the hydrogen adsorption free energy (ΔG_H*) changes from 1.92 eV on the pristine basal plane to −0.01 eV, approaching the ideal thermodynamic value. Detailed analysis of the correlation between the d-band center and ΔG_H* elucidates the microscopic origin of this optimization. Phonon dispersion and AIMD simulations confirm dynamical stability at room temperature. This work reveals the microscopic mechanism of strain–defect coupling in enhancing catalytic activity and provides a physical basis for the rational design of two-dimensional transition metal dichalcogenide electrocatalysts for clean energy applications.