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1.
Chemical bonding in representative astrophysically relevant neutral,cation, and anion HCnH chains 下载免费PDF全文
Ioan Baldea 《中国物理 B》2022,31(12):123101-123101
Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from ab initio computations for representative members of the astrophysically relevant neutral and charged HC2k/2k+1H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes, e.g., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC2k/2k+1H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study. 相似文献
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Zakieh Yousefi Hossein Eshtiagh‐Hosseini Alireza Salimi Janet Soleimannejad 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(5):386-393
In the title compound, [Cu(C7H3N2O4)(C4H5N2)(H2O)], (I), pyridine‐2,6‐dicarboxylate (pydc2−), 2‐aminopyrimidine and aqua ligands coordinate the CuII centre through two N atoms, two carboxylate O atoms and one water O atom, respectively, to give a nominally distorted square‐pyramidal coordination geometry, a common arrangement for copper complexes containing the pydc2− ligand. Because of the presence of Cu...Xbridged contacts (X = N or O) between adjacent molecules in the crystal structures of (I) and three analogous previously reported compounds, and the corresponding uncertainty about the effective coordination number of the CuII centre, density functional theory (DFT) calculations were used to elucidate the degree of covalency in these contacts. The calculated Wiberg and Mayer bond‐order indices reveal that the Cu...O contact can be considered as a coordination bond, whereas the amine group forming a Cu...N contact is not an effective participant in the coordination environment. 相似文献
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Reduction of Dimerization Tendency Due to the Decrease in Hybridization Index by Inclusion of 4s and 4p Semicore States as Valence States in Mon (n=2-18) Clusters: A First-Principles Study 下载免费PDF全文
Zhao-ye Gong Zhi-qiang Sun Yan-wen Ding Shuai Zhang Zhen-long Lv Xiao-fei Wang Li-ben Li Hai-sheng Li 《化学物理学报(中文版)》2021,34(5):639-648
Owing to the unique structural, electronic, and physico-chemical properties, molybdenum clusters are expected to play an important role in future nanotechnologies. However, their ground states are still under debate. In this study, the crystal structure analysis by particle swarm optimization (CALYPSO) approach is used for the global minimum search, which is followed by first-principles calculations, to detect an obvious dimerization tendency in Mo\begin{document}$ _n $\end{document} (\begin{document}$ n $\end{document} = 2\begin{document}$ - $\end{document} 18) clusters when the 4s and 4p semicore states are not regarded as the valence states. Further, the clusters with even number of atoms are usually magic clusters with high stability. However, after including the 4s and 4p electrons as valence electrons, the dimerization tendency exhibits a drastic reduction because the average hybridization indices \begin{document}$ H_{ \rm{sp}} $\end{document} , \begin{document}$ H_{ \rm{sd}} $\end{document} , and \begin{document}$ H_{ \rm{pd}} $\end{document} are reduced significantly. Overall, this work reports new ground states of Mo\begin{document}$ _n $\end{document} (\begin{document}$ n $\end{document} = 11, 14, 15) clusters and proves that semicore states are essential for Mo\begin{document}$ _n $\end{document} 相似文献
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Mixing ionic liquids (ILs) has been revealed as a useful way to finely tune the properties of IL-based solvents. The scarce available studies on IL mixtures have shown a quasi-ideal behavior of their physical properties. In this work, we have performed a thermophysical characterization of two binary IL mixtures, namely {4-methyl-N-butylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N]) + 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4])} and {[4bmpy][Tf2N] + 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate [emim][TFES]}. Both binary IL mixtures have been recently proposed as promising solvents in the (liquid + liquid) extraction of aromatic hydrocarbons from mixtures with alkanes. Densities, viscosities, refractive indices, thermal stability, and specific heats of the {[4bmpy][Tf2N] + [emim][EtSO4]} and {[4bmpy][Tf2N] + [emim][TFES]} IL mixtures have been measured as a function of both temperature and composition. Dynamic viscosities, refractive indices, and thermal stability of the {[4bmpy][Tf2N] + [emim][EtSO4]} mixture have exhibited strong deviations from the ideality, in contrast with the quasi-ideal properties of the {[4bmpy][Tf2N] + [emim][TFES]} mixture and the behavior of the imidazolium and pyridinium-based IL mixtures studied hitherto. The reliability of predictive methods of the thermophysical properties of the mixtures has also been evaluated. 相似文献
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Persistent homology has emerged as a popular technique for the topological simplification of big data, including biomolecular data. Multidimensional persistence bears considerable promise to bridge the gap between geometry and topology. However, its practical and robust construction has been a challenge. We introduce two families of multidimensional persistence, namely pseudomultidimensional persistence and multiscale multidimensional persistence. The former is generated via the repeated applications of persistent homology filtration to high‐dimensional data, such as results from molecular dynamics or partial differential equations. The latter is constructed via isotropic and anisotropic scales that create new simiplicial complexes and associated topological spaces. The utility, robustness, and efficiency of the proposed topological methods are demonstrated via protein folding, protein flexibility analysis, the topological denoising of cryoelectron microscopy data, and the scale dependence of nanoparticles. Topological transition between partial folded and unfolded proteins has been observed in multidimensional persistence. The separation between noise topological signatures and molecular topological fingerprints is achieved by the Laplace–Beltrami flow. The multiscale multidimensional persistent homology reveals relative local features in Betti‐0 invariants and the relatively global characteristics of Betti‐1 and Betti‐2 invariants. © 2015 Wiley Periodicals, Inc. 相似文献