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

Two-dimensional SiO₂ models (not DFT-optimized) as predicted by GRINSP

They can be porous too...

Models selected among 11157 CIF including 3D, 2D and 1D SiO₂

To be compared to the 4 models in a 2017 paper

Not exhaustive list (much more will be added during the next weeks)...

References for these predictions :

1- Inorganic structure prediction with GRINSP. A. Le Bail, J. Appl. Cryst. 38 (2005) 389-395. http://journals.iucr.org/j/issues/2005/02/00/cg5019/
2- Predicted corner-sharing titanium silicates. A. Le Bail, Z. Kristallogr., Suppl. 26 (2007) 203-208. https://www.researchgate.net/publication/228093494_Predicted_corner-sharing_titanium_silicates
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, Algérie (2005). http://arxiv.org/abs/cond-mat/0606025
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...