Fluxional and aromatic behavior in small magic silicon clusters:A full ah initio study of Si_n,Si_n~(1-),Si_n~(2-),and Si_n(1+),n=6,10 clusters

摘要

The structural,electronic,vibrational,optical,magnetic,and aromatic characteristics of Si_n,Si_n~(1-),Si_n~(2-),and Si_n~(1+),clusters have been calculated very accurately with a variety of high level ab initio techniques.These calculations have been performed with the aim to clarify existing ambiguities in the literature and to bring up the fluxional and aromatic characteristics of these species.The fluxional behavior,according to earlier conjecture of the present author,could be connected to the magic property.In addition such behavior could also explain the existence of conflicting results.The ab initio techniques include quadratic configuration interaction,coupled cluster,and multireference second order perturbation theory,together with density functional theory ("static" and time dependent) with the hybrid B3LYP functional.Various high quality correlation-consistent basis sets,ranging from 2Z up to 5Z quality,were employed.It is demonstrated that Si_6 is fluxional,fluctuating around a symmetric D_(4h) structure.Si_(10) is also fluxional but to a lesser degree,in contrast to Si_(10)~(1-) anion which is highly fluxional.For both clusters,in full agreement with Wade's and Lipscomb's rules for deltahedral boranes,the corresponding dianions have higher symmetry (O_h and D_(4d),respectively) and lower energy than the neutral clusters.The aromatic behavior of Si_6 fits better to a mixed conflicting aromaticity picture.This type of aromatic and fluxional behavior has also been observed in stable "magic" carbon clusters as C_6 and carbon fullerenes such as C_(20)-The present results,which support possible connection of fluxional and magic properties,are in excellent agreement with experimental measurements of ionization energies,electron affinities,and vibrationally resolved photoelectron spectra.