Structures, Thermochemical Properties, and Bonding
of Mixed Alkaline-Earth-Metal Silicon Trimers Si<sub>3</sub>M<sup>+/0/–</sup> with M = Be, Mg, Ca
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Abstract
The
ground state geometries, electronic structures, and thermochemical
properties of binary alkaline-earth-metal silicon clusters Si<sub>3</sub>M with M = Be, Mg, Ca in neutral, cationic, and anionic states
were investigated using quantum chemical computations. Lowest-lying
isomers of the clusters were determined on the basis of the composite
G4 energies. Along with total atomization energies, thermochemical
parameters were determined for the first time by means of the G4 and
coupled-cluster theory with complete basis set CCSD(T)/CBS approaches.
The most favored equilibrium formation sequences for Si<sub>3</sub>M clusters emerge as follows: all Si<sub>3</sub>M<sup>+/0/–</sup> clusters are formed by attaching the M atom into the corresponding
cation, neutral and anion silicon trimer Si<sub>3</sub><sup>+/0/–</sup>, except for the Si<sub>3</sub>Mg<sup>+</sup> and Si<sub>3</sub>Ca<sup>+</sup> where the metal cations are bound to the neutral Si<sub>3</sub>. The resulting mixed tetramers exhibit geometrical and electronic
features similar to those of the pure silicon tetramer Si<sub>4</sub><sup>+/0/–</sup>. Electron localization function (ELF) and
ring current analyses point out that the σ-aromatic character
of silicon tetramer remains unchanged upon substituting one Si atom
by one alkaline-earth-metal atom