Theoretical Chemistry Accounts最新文献

Abstract

We performed several types of ab initio calculations, from Hartree-Fock to Complete-Active-Space second-order perturbation theory and Coupled Cluster, on compact clusters of stoichiometry X (_4) Y (_4) , where X and Y are atoms belonging to the second row of the periodic table. More precisely, we considered the “cubic” structures of three isoelectronic groups, having a total of 48, 52, and 56-electrons, respectively. Notice that the highly symmetric cubic clusters of type X (_8) are characterized by an (O_h) symmetry group, while the X (_4) Y (_4) structures, with X (ne) Y, have at most a (T_d) symmetry. Binding energies and wave function analysis of these clusters have been performed, in order to investigate the nature, and the electron delocalization of these systems and establish a comparison between them. To this purpose, we also computed the Total-Position Spread tensor for each structure, a quantity which is related to the multi-reference nature of a system wave function.

This study focuses on investigating the spring properties of helicenes through DFT theoretical calculations. The energy change during stretching was observed by incrementally scanning the distance between both ends of the helicene from its stable state. The stiffness (k value) of each helicene was also determined at different stretching states. Interestingly, the k value was found to be non-constant during stretching, suggesting that helicenes do not behave as ideal springs. Furthermore, the effects of heteroatom doping and lateral π-extension on [6]helicene were examined, indicating that these factors have minimal impact on the spring nature of helicenes. Additionally, the study extended to longer helicenes, namely [12] and [18]helicenes. It was observed that the stiffness at the middle part of the helicene is greater than at the terminal parts, and the helical structures begin to collapse when the stretching length reaches approximately 2.5 times the stable state. We expected this work could bring innovative concept in future design of molecular devices.

γ-GeSe is a newly discovered two-dimensional (2D) material with exceptional electrical conductivity, which has generated significant interest in secondary ion battery. In this study, we have used first-principles calculations to evaluate the potential of γ-GeSe as an anode material for sodium-ion batteries. The results show that γ-GeSe has excellent stability properties with in-plane Young’s modulus as high as 30 Gpa and no imaginary frequencies in the phonon band spectrum. Upon adsorption of sodium, γ-GeSe undergoes a semiconductor-to-metal transition, enhancing electron conductivity. Moreover, Ab initio molecular dynamics calculations at room temperature (300 K) revealed the structural stability of γ-GeSe even after 10 ps of Na adsorption. We compute three distinct diffusion paths, with the lowest migration energy barrier of only 0.09 eV, indicating excellent migration rates. The calculated open-circuit voltage of 0.56 V (< 1 V) is crucial for anode material. Furthermore, the maximum theoretical capacity of γ-GeSe is determined to be 442 mAh/g. These findings provide valuable insights into the electrochemical energy storage potential of γ-GeSe as an anode material for sodium-ion battery.

Abstract

In the two-component relativistic density functional theory, the picture change error (PCE), which originates from insufficient transformation of operators, should be corrected. In this study, we examine the PCE in the fractional occupation number (FON) state based on the spin-free infinite-order two-component Hamiltonian. The PCE for the total and orbital energy changes is estimated with respect to the FON electrons of the highest occupied molecular orbital and 1s core orbital in noble gas atoms. PCE is significant in core orbitals in heavy elements but relatively small in light elements and valence orbitals. The delocalization error, which can be represented by the total energy deviation from the behavior of the exact energy, is overestimated by the lack of picture change correction of the two-electron operator and underestimated by that of the density operator. Corresponding to these results, the PCE influences the value of orbital energies and slope of orbital energy change to FON.

Abstract

The choice of solvent plays a crucial role in aldol reactions, often affecting both the conversion rate and stereoselectivity. In this study, we investigated the influence of solvents (water, methanol and hydroalcoholic) on the proline-catalyzed aldol reactions. We focused on elucidating the solute–solvent interactions at the rate-determining step and the stereoselective step. Our theoretical finding suggests, hydroalcoholic-mediated reaction exhibits a higher conversion rate as compared to pure water and pure methanol-mediated system with the generation of most stable transition state structure. This can be attributed to the existence of strong hydrogen bonding and the formation of stable six-membered transition state structures in hydroalcoholic-mediated system. In addition to this, our research demonstrates that the choice of solvent plays a crucial role in determining the percentage of enantiomeric excess in the reaction. Theoretical finding suggest that the anti-product is preferentially formed in the presence of water and hydroalcoholic media as solvents. Pure water and hydroalcoholic solvents surprisingly showed a higher enantiomeric excess for the anti-product due to formation of strong hydrogen bonding between reaction moiety and solvents. In contrast, methanol-assisted reactions resulted in a racemic mixture, consistent with experimental observations. Results reported in the present study contribute to the broader understanding of solvent effects in organic reactions and offer valuable insights for the design of organic reactions.

The current work investigated the interaction of ZnO nanoparticles (NPs) with glycine, tyrosine, methionine and phenylalanine. (ZnO)₁₂ cage-like cluster was modeled using the density functional theory to determine the adsorption energy, the preferred sites for adsorption of amino acids, and the electronic structure of the formed complexes. The findings suggest that pure amino acids interact with (ZnO)₁₂ via a chemisorption process. The thermodynamic parameters computed showed that the complexation is an exothermic process and enthalpy-driven. The oxygen atoms in the carboxyl groups of the four studied amino acids are involved in the adsorption process. PHE_Zn₁₂O₁₂ exhibits the highest adsorption energy (− 207.50 kJ/mol) due to its interaction with the Zn₁₂O₁₂ nanocluster through two different adsorption sites. The electronic and sensing properties were examined by analyzing the HOMO and LUMO energies and the HOMO–LUMO energy gap (|ΔEg|). The sensitivity of Zn₁₂O₁₂ nanocluster toward the studied amino acids was examined by comparing the percentage variation of the gap after the adsorption, which can reach the value of 38%, suggesting the potential of Zn₁₂O₁₂ nanocluster as a promising sensor for the detection of amino acids. Interaction region indicator (IRI) analysis was performed for a visual understanding of the different interactions occurring between the amino acids and the Zn₁₂O₁₂ nanocluster. The results of this study can shed some light on the possible application of ZnO-based nanobiosensors for detecting protein tyrosine/tryptophan nitration as an early symptom of several serious chronic diseases.

The primary objective of this study was to utilize high-level density functional theory calculations to optimize the synthetic parameters for a molecularly imprinted polymer (MIP) targeting cyhalothrin, a synthetic pyrethroid insecticide. A systematic structural and energetic analysis was performed to investigate various functional monomers, solvents, and cross-linker agents in order to obtain the optimal MIP synthetic conditions. The main findings indicate that p-vinylbenzoic acid, is the optimal functional monomer, chloroform are effective solvents, and pentaerythritol triacrylate is the recommended cross-linking agent. We firmly believe that this rational design offers valuable insights to experimentalists seeking to efficiently synthesize a MIP for the selective extraction of this widely used insecticide, thereby avoiding wasted laboratory resources and achieving high extraction yields.

Inspired by the remarkable photochemical and photophysical properties of novel 2-(2′-hydroxyphenyl)benzothiazole (HBT) derivatives that could be potentially applied across various disciplines, in this work, effects of solvent polarity on excited state hydrogen bond effects and excited state intramolecular proton transfer (ESIPT) reaction of 5-{2-[2-(4-amino-phenyl)-2,3-dihydro-benzofuran-6-yl]-vinyl}-2-benzothiazol-2-yl-phenol (E-HBT) are focused. By comparing the structural changes and infrared (IR) vibrational spectra of the E-HBT fluorophore in polar acetonitrile, moderate polar dichloromethane and nonpolar cyclohexane solvents, combined with the preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we can conclude that the hydrogen bond could be strengthened in S₁ state, which is favorable for the occurrence of ESIPT reactions. The charge recombination behavior of hydrogen bond induced by photoexcitation also further illustrates this point. Via constructing potential energy curves (PECs) based on restrictive optimization and searching transition state (TS) form, we confirm change of surrounding solvent polarity has a regulatory effect on the ESIPT behavior for E-HBT, that is, the higher the polarity of the solvent, the more favorable it is for the ESIPT reaction.

Temperature, concentration and pore size constitute critical factors influencing adsorption and diffusion in tobacco. Investigating the adsorption and diffusion behavior of tobacco not only advances fundamental theory but also provides practical guidance for the tobacco industry to optimize cigarette quality and performance through adjustments in production conditions. This study reports a multiscale simulation framework exploring the adsorption and diffusion of water, propylene glycol, glycerol and nicotine under the influence of these key factors. First-principles density functional theory calculations reveal the preference of H₂O to adsorb on O-top rather than H-top sites due to weak hydrogen bond interactions. Additionally, molecular dynamics simulations demonstrate that with increase in temperature, the diffusion properties of H₂O and other components enhance, attributed to intensified thermal vibrations and increased kinetic energy of the adsorbent. Intriguingly, with increase in concentration, the diffusion properties of all adsorbents initially increase and then decrease, intricately linked to hydrogen bond effects on system stability and the availability of accommodation space in the porous structure of cellulose. Furthermore, as pore size enlarges, the diffusion of adsorbents significantly increases due to the expansion of free space. In summary, the objective of this study is to provide a profound theoretical understanding for the cigarette industry, thereby contributing to the improvement of cigarette quality and flavor.

Density functional theory is widely used to theoretical investigation and comparison of electrode materials. In this paper, we propose novel theoretical approach to evaluate cyclability of intercalation electrode materials. Crystal structure of an intercalation electrode material have to be stable after deintercalation, which is called “structural stability”. Capability of an electrode to endure many cycles is called as “cyclability”. We suggest that changing in properties in atomic scale under intercalation/deintercalation (cycling) is responsible for low cyclability, while changing in cell parameters and unit cell properties is responsible for the primitive structural stability. Also, thermodynamic stability of the electrode polymorph after deintercalation can be another parameter of structural stability. We use layered oxides and spinel electrode materials, to verify the here proposed approach, respectively, for atomic forces and magnetic moment. As a consideration in analysis of calculated forces, LiCoO₂ is estimated to have the most stable cycling in the family. According to the results, Fe atoms in LiFeO₂ would experience huge changes in the force value after (de)lithiation, causing low cyclability, as observe in experiments. In term of changes in magnetic moment under (de)lithiation, our calculations show significant changes of magnetic moment for LiMn₂O₄, which justifies its low cyclability observed in the experimental studies.