Magic number silicon dioxide-based clusters: laser ablation-mass spectrometric and density functional theory studies

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Laser ablation of porous siliceous materials produces magic number silica clusters.
• Understanding the atomic structure of these clusters is crucial for materials science.

Purpose of the Study:

• To investigate the structural origins of magic number silica clusters [(SiO(2))(n)O(2)H(3)](-) with n=4 and n=8.
• To provide a theoretical interpretation for the observed magic numbers and the absence of higher ones.

Main Methods:

• Density Functional Theory (DFT) calculations at the B3LYP/6-31G** level.
• Global structure searching using a genetic algorithm.
• Optimization of geometries and calculation of vibrational frequencies for various silica cluster configurations.

Main Results:

• DFT predicts pseudotetrahedral cage-like structures for the n=4 magic number cluster and its anion.
• The bare silica octamer (n=8) exhibits a linear chain structure.
• The n=8 complex cluster and its anion show a mixture of cubic cage-like and quasi-bicage structures, stabilized by O and H atoms.

Conclusions:

• Theoretical calculations provide a structural basis for the observed magic number silica clusters (n=4 and n=8).
• The stabilization mechanisms involving oxygen and hydrogen atoms are identified.
• The study offers preliminary insights into why higher magic numbers are not observed.