See what you will probably never see in reality, thanks to the PCOD...

Three-dimensional SiO2 models with lowest framework density (FD) as predicted by GRINSP

Models extracted from the PCOD 2009 update

(Selected among 11695 CIF including 3D, 2D and 1D SiO2 models)

Not exhaustive list, run again GRINSP and you will find more...

References for these predictions :

1- Inorganic structure prediction with GRINSP. A. Le Bail, J. Appl. Cryst. 38 (2005) 389-395.
2- Predicted corner-sharing titanium silicates. A. Le Bail, Z. Kristallogr., Suppl. 26 (2007) 203-208.
3- Powerpoint file : Contribution to the "Gordon Conference Style" Workshop : Global Optimisation Techniques Applied to the Prediction of Structures, 5-7 July 2006, University College London (.ppt or zipped)
4- Advances in structure prediction of inorganic compounds. A. Le Bail, Report of 2nd Algerian Crystallography Congress, AlgĂ©rie (2005).
5- Hypothetical AlF3 crystal structures, A. Le Bail, F. Calvayrac, J. Solid State Chem., 179 (2006) 3159-3166.
6- Inorganic structure prediction: too much and not enough, A. Le Bail, Solid State Phenomena 130 (2007) 1-6.
7- Frontiers between crystal structure prediction and determination by powder diffractometry, A. Le Bail, Powder Diffraction, S23 (2008) S5-S12.
8- Databases of virtual inorganic crystal structures and their applications, A. Le Bail, Phys. Chem. Chem. Phys. 12 (2010) 8521-8530. DOI: 10.1039/c003907c
Etc - search by yourself after all...

1- PCOD3101110  FD = 9.48   CIF

2-PCOD3101817   FD = 10.19   CIF

3-PCOD3101685   FD = 10.23   CIF