SiO2 Boisen M B, Gibbs G V, Bukowinski M S T Physics and Chemistry of Minerals 21 (1994) 269-284 Framework silica structures generated using simulated annealing with a potential energy function based on an H6Si2O7 molecule Sample: 22 _database_code_amcsd 0007887 4.2166 4.0206 7.6423 90 119.6668 90 Pc atom x y z Si1 0 .49891 0 Si2 .30231 .10448 .37836 O1 .34155 .26088 .58341 O2 .68329 .20774 .38310 O3 .13105 .27048 .86496 O4 .98917 .30762 .18536