-    CRISTOBALITE X-I     -    SiO2

2x1x1 super structure. The crystal structure is fully relaxed (both unit cell parameters and atomic positions under symmetry constraints) at 10GPa. 

Crystal Structure 


Because of the translational symmetry all the calculations are performed in the primitive unit cell and not in the conventional unit cell. The following information regarding the structure is given with respect to this primitive unit cell, which sometimes can take an unintuitive shape.

Symmetry (experimental): 

Space group:  Theo 14  Theo P2_1/n 
Lattice parameters (Å):  6.7500  4.0633  6.8344 
Angles (°):  90  90  90 

Symmetry (theoretical): 

Space group:  Theo 14  Theo P2_1/n 
Lattice parameters (Å):  12.8731  3.8829  6.6716 
Angles (°): 

Cell contents: 

Number of atoms:  48 
Number of atom types: 
Chemical composition: 

Atomic positions (theoretical):

Si:  0.2508  0.0002  0.5013 
Si:  0.9959  0.4984  0.0008 
Si:  0.1787  0.9983  0.1178 
Si:  0.0697  0.5021  0.3759 
Si:  0.3209  0.0021  0.8831 
Si:  0.4325  0.5006  0.6255 
Si:  0.1358  0.4969  0.7584 
Si:  0.3632  0.5050  0.2441 
O:  0.1660  0.2247  0.3323 
O:  0.0822  0.7325  0.1664 
O:  0.3355  0.7743  0.6703 
O:  0.4183  0.2599  0.8346 
O:  0.2336  0.2345  0.7120 
O:  0.0223  0.7200  0.7949 
O:  0.2660  0.7656  0.2897 
O:  0.4767  0.2794  0.2056 
O:  0.1517  0.7314  0.5458 
O:  0.1027  0.2538  0.9567 
O:  0.3501  0.2688  0.4569 
O:  0.3961  0.7446  0.0439 
O:  0.2114  0.7614  0.9210 
O:  0.0439  0.2813  0.5813 
O:  0.2882  0.2385  0.0808 
O:  0.4549  0.7269  0.4164 
Si:  0.7458  0.0019  0.5004 
Si:  0.5008  0.4992  0.0012 
Si:  0.6812  0.9959  0.1184 
Si:  0.5670  0.4996  0.3753 
Si:  0.8192  0.9974  0.8748 
Si:  0.9308  0.5047  0.6174 
Si:  0.6359  0.4938  0.7570 
Si:  0.8852  0.0043  0.2589 
O:  0.6647  0.2332  0.3306 
O:  0.5834  0.7400  0.1675 
O:  0.8331  0.7666  0.6659 
O:  0.9155  0.2682  0.8306 
O:  0.7328  0.2327  0.7090 
O:  0.5233  0.7198  0.7959 
O:  0.7721  0.7810  0.2951 
O:  0.9824  0.2669  0.2099 
O:  0.6485  0.7319  0.5441 
O:  0.6054  0.2527  0.9577 
O:  0.8536  0.2489  0.4567 
O:  0.8997  0.7679  0.0450 
O:  0.7121  0.7514  0.9187 
O:  0.5444  0.2728  0.5844 
O:  0.7939  0.2191  0.0814 
O:  0.9623  0.7491  0.4196 
Atom type 

We have listed here the reduced coordinates of all the atoms in the primitive unit cell.
It is enough to know only the position of the atoms from the assymetrical unit cell and then use the symmetry to build the whole crystal structure.

Visualization of the crystal structure: 

Size:

Nx:  Ny:  Nz: 
You can define the size of the supercell to be displayed in the jmol panel as integer translations along the three crys­tallo­gra­phic axis.
Please note that the structure is represented using the pri­mi­tive cell, and not the conventional one.
 

Parameters of the Calculation 


All the calculations have been done using the ABINIT software. This is a list of the most representative parameteres used during the Raman calculation.


Number of electronic bands: 128
k-points  
   grid: 4 4 4 
   number of shifts: 
   shifts: 0.5 0.5 0.5 
Kinetic energy cut-off: 40 Ha  [=1088.464 eV ]
eXchange-Correlation functional:  

Pseudopotentials: 
Si:  silicon, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local 
O:  oxygen, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local