Search

A recently proposed local Fukui function is used to predict the binding site of atomic hydrogen on silicon clusters. To validate the predictions, an extensive search for the more stable SinH (n=3–10) clusters has been done using a modified genetic algorithm. In all cases, the isomer predicted by the Fukui function is found by the search, but it is not always the most stable one. It is discussed that in the cases where the geometrical structure of the bare silicon cluster suffers a considerable change due to the addition of one hydrogen atom, the situation is more complicated and the relaxation effects should be considered. [ABSTRACT FROM AUTHOR]

Photoelectron spectra of anionic clusters of silicon require reliable theoretical calculations for their assignment and interpretation. Electron propagator calculations in the outer valence Green’s-function approximation with two well-characterized, all-electron basis sets on vertical electron detachment energies (VEDEs) of anions are compared to similar calculations that employ Stuttgart pseudopotentials. Tests on Sin- clusters with n=3–7 exhibit an encouraging agreement between the all-electron and pseudopotentials results and between electron propagator predictions and experiments and values obtained from coupled-cluster calculations. To illustrate the capabilities of the new approach based on a Si pseudopotential and electron propagator methods, VEDE calculations on Si10- are presented. [ABSTRACT FROM AUTHOR]

Photoelectron spectra of anionic clusters of silicon require reliable theoretical calculations for their assignment and interpretation. Electron propagator calculations in the outer valence Green’s-function approximation with two well-characterized, all-electron basis sets on vertical electron detachment energies (VEDEs) of anions are compared to similar calculations that employ Stuttgart pseudopotentials. Tests on Sin- clusters with n=3–7 exhibit an encouraging agreement between the all-electron and pseudopotentials results and between electron propagator predictions and experiments and values obtained from coupled-cluster calculations. To illustrate the capabilities of the new approach based on a Si pseudopotential and electron propagator methods, VEDE calculations on Si10- are presented. [ABSTRACT FROM AUTHOR]

The potential energy surfaces of the [Si.sub.5][Li.sub.n.sup.5-6] (n = 5?7) systems were explored in detail to find feasible way to design three-dimensional star-like silicon structures using the appropriate ligands. The calculation results revealed that the important contribution of ionic character of the Si-Li interactions to induce the formation of a bridged structure and the contribution of reduction of the Pauli repulsion and the maximization of the orbital towards formation of star-like structure.

A range of cyclin-dependent kinases (CDK2) inhibitors are analyzed by a model of active site called the hinge region (HR) by utilizing a group of global reactivity indices decided with respect to density of states. It is proposed that in the HR-ligand interaction, the polarization effect is more than the charge transfer contribution by comparing the biological activity and global softness.

A simple model is presented to develop an empirical nucleophilicity scale based on the stretching force constants of the vibrational spectrum, where the B-HX hydrogen bonding system (where B is a base Lewis and HX is a dipole) is the benchmark to test the model. The results have shown that Legon and Millen nucleophilicity scale and the electrostatic potential derived scales can elucidate in good approximation the reactivity order of the nucleophiles only when the interactions with a probe electrophile is of the hard-hard type.

Extensive explorations of their potential energy surfaces, combined with high‐level quantum chemical computations, strikingly show that the lowest energy structures of the (Li6Si5)2–5 systems consist of 2–5 Si56− aromatic units, surrounded by Li+ counterions, respectively. These viable gas‐phase compounds are the pioneering reported cases of oligomers made by planar aromatic silicon rings. Based on the key evidence that these oligomers are energetically favored, and that their silicon rings aromaticity is thoroughly preserved, the Li6Si5 cluster is proposed as a potential assembly unit to build silicon‐lithium nanostructures, thus opening new paths to design Zintl compounds at the nanoscale level. Aromatic building blocks: After a systematic exploration of the potential energy surface of the (Li6Si5)2–5 clusters, it was found that the lowest energy structures in all cases are formed by multiple aromatic Si56− pentagonal units interacting electrostatically with lithium cations. These units maintain their geometric and electronic properties as revealed by chemical bonding and magnetic response analyses. [ABSTRACT FROM AUTHOR]

We present new evidence that supports the aromatic character of the clusters of formula: [M3(µ‐X)3X6]0/2– (M = Re and Tc, X = Cl, Br, I). Our computations clearly show that these clusters present a special response to an applied external magnetic field, which is characteristic of aromatic systems. Both analyzed response properties, the magnetically induced current density and the induced magnetic field, agree that the magnetic perturbation induces two concentric diatropic ring currents: the inner one inside the M3 core and the outer one around the M3(µ‐X)3 triangle. The flow strength of these two ring currents is significant, confirming the high diatropicity of these clusters. In the dianionic species, aromaticity is increased, mainly by an increment of the diatropicity of the inner ring current. These findings support a chemical bonding pattern with delocalized M–M bonds in these species. [ABSTRACT FROM AUTHOR]

Abstract: Herein we report the systematic exploration of the potential energy surfaces of a series of clusters with formula E5M7+ (E=C‐Pb and M=Li‐Cs). Fifteen of these combinations adopt a D5h three‐dimensional seven‐pointed star‐like structure in a singlet state, where M atoms interact electrostatically with the E5 ring. The determining factors in the relative preference of having the D5h structure over the most competitive isomer or vice‐versa are analyzed. These star‐shaped systems satisfy the 4n+2 Hückel's rule and exhibit a strong diatropic (σ and π) response to an external magnetic field. [ABSTRACT FROM AUTHOR]

Theoretical studies are essential for the structural characterization of clusters, when it comes to rationalize their unique size-dependent properties and composition. However, the rapid growth of local minima on the potential energy surface (PES), with respect to cluster size, makes the candidate identification a challenging undertaking. In this article, we introduce a hybrid strategy to explore the PES of clusters. This proposal involves the use of a biased initial population of a genetic algorithm procedure. Each individual in this population is built by assembling small fragments, according to the best matching of the Fukui function. The performance of a genetic algorithm procedure. The performance of the method is assessed on the PES exploration of medium-sized Si n clusters ( n = 12-20). The most relevant results are: (a) the method converges at almost half of the time used by the canonical version of the GA and, (b) in all the studied cases, with the exception of Si13 and Si16, the method allowed to identify the global minimum (GM) and other important low-lying structures. Additionally, the apparent deficiency of the proposal to identify the GM was corrected when a Si atom, or other low-lying isomers, were considered to build the clusters. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this paper, we provide solid evidence to show that among an overwhelming structural diversity, alkaline earth metals (Ca, Sr, Ba) have the ability to form inverted sandwich compounds with C6H6, C7H7+, and C8H82+ of Dnh symmetry and general formula [E–(CnHn)–E]n−6 (n = 6–8) with planar 10-π-electron aromatic cores by virtue of transferring two electrons per metal atom to the ring. However, the origin of the orbital interaction between the metals and the carbon ring is quite different; while [E–(C6H6)–E] complexes are dominated by δ-interactions, both π- and δ-interactions are important in [E–(C7H7)–E]+ and [E–(C8H8)–E]2+ complexes. [ABSTRACT FROM AUTHOR]

The stability of the LinBnH2n (n = 3–6) series was analyzed using quantum chemical calculations, and it was found that cyclic isomers are not energetically favored. This is different to what happens in their organic counterparts (CnH2n), where cyclopentane (C5H10) and cyclohexane (C6H12) are the low-lying isomers. Apparently, aromaticity is a key-stabilizing factor that needs to be considered for designing stable lithium-boron hydride analogues of cyclic organic compounds. This is verified in the Li3B3H3+ system, which has been designed as the smallest aromatic carbocation (C3H3+) analogue. The global minimum structure of Li3B3H3+ contains a triangular B3H32− moiety, which has structural and chemical bonding features similar to its organic counterpart. Besides, this new cluster is classified as aromatic according to both the 4n + 2 Hückel rule and the analysis of the induced magnetic field. This theoretical evidence leads us to propose this cluster as a viable target for experimental detection in the gas phase. [ABSTRACT FROM AUTHOR]