Neutral and cationic free-space oxygen-silicon clusters <tex>SiO_{n}$</tex> (<tex>1\lt n\leq 6$</tex>), and possible relevance to crystals of <tex>SiO_{2}$</tex> under pressure

Motivated by the theoretical study of Saito and Ono (2011) on three crystalline forms of SiO2 under pressure, quantum-chemical calculations on various free-space clusters of SiOn and GeOn for 1 < n