Journal of Computational Chemistry最新文献

The ring-expansion of the parent phenylphosphinidene (2) to 1-phospha-1,2,4,6-cycloheptatetraene (3) has been theoretically predicted; however, this isomer remains yet unobserved in previous experimental studies. Herein, we report the observation of 2 and 3 during photolytic (193 nm) dehydrogenation of phenylphosphine (1) in an Ar-matrix at 10 K. Upon subsequent photoexcitation at 365 nm, 3 prefers association with molecular hydrogen in the cryogenic matrix by reformation of 1; whereas, no interconversion between 3 and 2 could be observed under the irradiation conditions. When using phenylphosphine chloride (4) as the precursor, the 1:1 complex of 2 with HCl (2–HCl) stabilized by intramolecular ClH•••π hydrogen bond is generated in the matrix, and it undergoes photo-induced phosphinidene insertion into HCl by reformation of 4 upon photoexcitation at 365 nm. By photolyzing the matrix-isolated complex of 1 with molecular chlorine (1–Cl₂) at 310 nm, the 1:2 hydrogen-bonded complexes of 2 with HCl are efficiently generated. Further photoexcitation of 2–2HCl at 193 nm causes ring expansion in yielding of 3–2HCl, and the reverse ring contraction from 3–2HCl to 2–2HCl occurs upon subsequent photoexcitation at 365 nm. The identification of 3 and the hydrogen-bonded complexes 2–HCl, 2–2HCl, and 3–2HCl with matrix-isolation IR and UV–vis spectroscopy is supported by quantum chemical calculations at the B3LYP-D3/6-311++G(3df,3pd) level of theory.

This work investigates the direct and superexchange couplings in donor–bridge–acceptor electron transfer molecules by extracting diabatic information from the adiabatic wave functions obtained from multiconfigurational self-consistent field methods. Based on the numerical values of these couplings, the electron transfer mechanisms are derived for the three model systems, including 1,4-diazabicyclo[2.2.2]octane radical cation, [3,3]-spirarene, and [Fe(H₂O)₆—H₂O—Fe(H₂O)₆]⁵⁺, namely that spirarene and the other two molecules are controlled by the direct and superexchange mechanisms, respectively.

The counterpoise (CP) method, widely used to evaluate the basis set superposition error (BSSE) inherent in the supermolecular approach, is critically examined in the study of noncovalent interaction between rare gas atoms. Potential energy curves for the rare gas dimers (He₂, Ne₂, and Ar₂) are calculated with and without CP correction using the aug-cc-pVxZ basis sets (x = D, T, Q, 5) at multiple levels of theory (HF, MP2, MP4, and CCSD(T)). While CP correction effectively removes BSSE in the HF energy, which constitutes the major component of the total energies, in contrast, applying the CP correction energy to the electron correlation energy yields a positive BSSE, leading to systematically shallower potential energy curves, particularly when smaller basis sets are employed. We analyzed this contrasting behavior of the HF and electron correlation energy components in terms of the orbital basis inconsistency (OBI) and configuration basis inconsistency (CBI).

Pectin, a major class of matrix polysaccharides present in plant cell walls (PCW), contains widespread anionic saccharides that cross-link in the presence of cations. It modulates important functions such as cell–cell adhesion and determines the PCW's biomechanical properties. It is known that mono-, di-, and tri-valent cations facilitate cross-linking; however, significant knowledge gaps remain in understanding the structure and mechanism of pectin cross-linking. In this study, replica-exchange molecular dynamics (REMD) simulations were employed to elucidate the role of ionic charge, ionic radii, and functional groups on the cross-linking of homogalacturonan (HG), the most abundant pectin molecule. Our enhanced sampling approach in fully solvated environments suggests more effective cross-linking with higher-valent and smaller ions, and that the “zipper” conformation is more favorable than the prevalent “egg-box” conformation. These findings advance our fundamental understanding of pectin matrix structure in PCWs and provide a solid foundation to probe structure–property relationships in pectic polysaccharides.

The chemical stability and performance of non-fullerene acceptors (NFAs) are critical for achieving high power conversion efficiency (PCE) and device stability. This study presents a novel computational design strategy for addressing key stability challenges. The photochemical stability is improved by removing the vinylene bridge between the core and end groups, which often causes degradation and photoisomerization. All-fused non-fullerene acceptors (AFNFAs) are designed by directly fusing high-performance end groups with core units such as Y6 (FY6) and ITIC (FITIC). Density functional theory (DFT) and molecular dynamics simulations show that the new molecules exhibit superior optoelectronic properties and favorable bulk-phase morphologies. The results also show highly ordered packing of acceptor dimers and efficient charge transport. Additionally, the voltage losses associated with exciton diffusion, dissociation, and energetic disorder in electron affinities are minimal. Overall, the proposed AFNFAs with imide end groups emerge as promising candidates for stable high-performance acceptors in organic solar-cell applications.

This paper offers a reliable methodology to calculate HOMO-LUMO energy gaps in furan-fused helicenes ([n]FH) by employing 16 DFT functionals (B3LYP, B3LYP-D, B3LYP-D3, B3LYP-D3BJ, CAM-B3LYP, LC-BLYP, HSE06, LC-ωPBE, M06, MN15, PBE0, PBe0DH, ωB97XD, B2PLYP, B2PLYP-D3, and B2PLYP-D3BJ). The fundamental gaps (ΔE_CCSD(T) = IE − EA) are used as reference values for a reliable benchmark for energy gaps for oxa[n]helicenes ([n]FH, n = 1–4). [n]FH yields blue-shifted HOMO-LUMO gaps relative to sulfur-, selenium-, and tellurium-based analogues. A dimerization study reveals that oxa[n]helicenes are very resistant to dimerization in DCM solvent in neutral as well as cationic states. MD simulations using the COMPASSIII force field in DCM solvent demonstrate that oxa[n]helicenes are highly resistant to dimerization in cationic states in the presence of $��{\mathrm{PF}}_6^{-}�$ counter ions. Optimally tuned ω values for LC-ωPBE, LC-BLYP, and ωB97XD in DCM (SMD solvation model) are almost ~20 to 100 times less than those in the gas phase, with the HOMO-LUMO gaps in solvent much smaller. In addition, PBC-DFT calculations reveal that the band gap obtained at PBC-PBE0 and PBC-B3LYP levels is quite comparable to the energy gap obtained at optimally tuned ω values for LC-ωPBE, LC-BLYP, and ωB97XD in DCM solvent. HOMO-LSOMO gaps of oxa[n]helicene radical cations also blueshift compared to their S-, Se-, and Te-based counterparts. TDDFT calculation with CAM-B3LYP functional shows intense infrared absorption in furan-based helicene radical cations, reflecting optoelectronic potential. This research emphasizes that the accuracy in excited-state properties can be achieved with optimally tuned LC-ωPBE, LC-BLYP, and ωB97XD functionals, which are quite comparable to results obtained with the CAM-B3LYP functional for neutral and radical cations of oxa[n]helicenes. These radical cation systems showed comparable absorption in the infrared range like S-systems. Overall, our benchmarking studies lead to better predictions of HOMO-LUMO gaps of oxa[n]helicenes. This work offers the much-needed insights into the design of furan-based helicene, opening doors to future advanced organic materials for electronics and photonics technology.

Excited states of systems composed of linked fragments or stacked molecules are important for understanding their optoelectronic properties. These states, when projected to individual fragments, are either local (LEs) or charge transfer excitons (CTEs). However, the canonical molecular orbitals (CMOs) obtained from a typical calculation tend to delocalize, which makes the subsequent analysis of excited states cumbersome. In this work, we report a simple approach to address this problem by employing localized molecular orbitals (LMOs) as linear combinations of the CMOs in the occupied and virtual subspaces separately after a self-consistent field calculation. This separated linear combination ensures that configuration interaction singles (CIS), random phase approximation (RPA), and their corresponding density functional theory (DFT) counterparts [Tamm-Dancoff approximation time-dependent DFT (TDA-TDDFT) and TDDFT] calculations with LMOs are mathematically equivalent to those performed with CMOs. We performed tests on simple symmetric and asymmetric dimer systems and found that the excited states are numerically identical in excitation energies and transition moments for both LMOs and CMOs, except for very few states that are only found in either LMO or CMO (in symmetric cases). The LMO basis makes both qualitative and quantitative analyses of the excited states much more accessible, as the extent of LE and CTE contributions can be easily defined. Consequently, this simple yet robust approach can be useful for characterizing excitons in multichromophoric systems and in condensed phases, which is useful when studying problems pertaining to electron/excitation energy transfer processes.

The dipole moment is a simple electronic property with widespread experimental and theoretical applications. Using vibrational second-order perturbation theory (VPT2) and density functional theory (DFT), we calculate the dipole moments of 125 small molecules. While it is known that vibrational effects can significantly affect the dipole moments of molecules, there has been no large-scale study that assessed the effectiveness of including vibrational effects in dipole moment calculations using DFT-VPT2. We find that DFT-VPT2 dipole moments calculated with the aug-cc-PVTZ basis set and averaged across a variety of exchange-correlation functionals when compared to DFT dipole moments with no vibrational corrections have an absolute mean error that is lower by 0.003 Debye, a mean absolute error that is lower by 0.005 Debye, a mean percentage error that is lower in units of percentage points by 0.1, and a root mean squared error that is lower by 0.009 Debye relative to experiment for a test set of 125 small molecules. Calculated dipole moments are also often used as a proxy for the accuracy of the electronic density distribution. We investigate the correlation between dipole moments and electronic densities using a measure of the electron density error based on density profiles computed in a previous study (J. Phys. Chem. Lett. 2017 8 (15) 3488). We find that the correlation between the accuracy of the calculated dipole moment and the electronic density error is weak (all R² values are less than 0.5), suggesting that dipole moments are an inadequate metric for assessing electronic density errors. Based on the results in this study, we find it unnecessary to include VPT2 vibrational effects when using DFT to compute dipole moments, as any increase in accuracy is limited.