-    CRISTOBALITE     -    SiO2

The crystal structure is fully relaxed (both unit cell parameters and atomic positions under symmetry constraints) starting from an experimental structure similar to the one reported in AMCSD 

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:  92  P4_12_12 
Lattice parameters (Å):  4.9717  4.9717  6.9223 
Angles (°):  90  90  90 

Symmetry (theoretical): 

Space group:  92  P4_12_12 
Lattice parameters (Å):  4.9507  4.9507  6.8964 
Angles (°):  90  90  90 

Cell contents: 

Number of atoms:  12 
Number of atom types:  2 
Chemical composition:  0 

Atomic positions (theoretical):

Si:  0.3000  0.3000  0.0000 
O:  0.2392  0.1041  0.1787 
Si:  0.2000  0.8000  0.2500 
O:  0.3959  0.7392  0.4287 
O:  0.2608  0.6041  0.0713 
Si:  0.7000  0.7000  0.5000 
O:  0.7608  0.8959  0.6787 
O:  0.8959  0.7608  0.3213 
O:  0.1041  0.2392  0.8213 
Si:  0.8000  0.2000  0.7500 
O:  0.6041  0.2608  0.9287 
O:  0.7392  0.3959  0.5713 
Atom type  X  Y  Z 

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.
     

Powder Raman 

Powder Raman spectrum

The intensity of the Raman peaks is computed within the density-functional perturbation theory. The intensity depends on the temperature (for now fixed at 300K), frequency of the input laser (for now fixed at 21834 cm-1, frequency of the phonon mode and the Raman tensor. The Raman tensor represents the derivative of the dielectric tensor during the atomic displacement that corresponds to the phonon vibration. The Raman tensor is related to the polarizability of a specific phonon mode.

Choose the polarization of the lasers.

I ∥ 
I ⊥ 
I Total 
Horizontal:
Xmin:
Xmax:
Vertical:
Ymin:
Ymax:
 

Data about the phonon modes

Frequency of the transverse (TO) and longitudinal (LO) phonon modes in the zone-center. The longitudinal modes are computed along the three cartesian directions. You can visualize the atomic displacement pattern corresponding to each phonon by clicking on the appropriate cell in the table below.

1
ac
0
0
0
0
2
ac
0
0
0
0
3
ac
0
0
0
0
4
B1
39
39
39
39
1.354e+37
0.0
1.016e+37
0.0
2.370e+37
0.0
5
B1
111
111
111
111
2.511e+39
5.2
1.883e+39
3.9
4.395e+39
9.1
6
E
142
142
142
142
7
E
142
143
143
142
8
A1
219
219
219
219
3.862e+40
80.0
2.269e+38
0.5
3.884e+40
80.5
9
E
265
265
265
265
4.295e+38
0.9
5.906e+38
1.2
1.020e+39
2.1
10
E
265
265
265
265
4.295e+38
0.9
5.906e+38
1.2
1.020e+39
2.1
11
B2
278
278
278
278
3.849e+38
0.8
5.293e+38
1.1
9.142e+38
1.9
12
A2
288
288
288
298
13
A1
357
357
357
357
6.832e+38
1.4
8.065e+36
0.0
6.912e+38
1.4
14
B1
368
368
368
368
6.268e+37
0.1
4.701e+37
0.1
1.097e+38
0.2
15
E
373
373
373
373
6.047e+36
0.0
8.314e+36
0.0
1.436e+37
0.0
16
E
373
378
378
373
6.047e+36
0.0
8.315e+36
0.0
1.436e+37
0.0
17
A1
404
404
404
404
4.800e+40
99.4
2.875e+38
0.6
4.828e+40
100.0
18
B2
432
432
432
432
1.588e+37
0.0
2.184e+37
0.0
3.772e+37
0.1
19
E
458
458
458
458
3.895e+36
0.0
5.356e+36
0.0
9.251e+36
0.0
20
E
458
482
482
458
3.896e+36
0.0
5.357e+36
0.0
9.253e+36
0.0
21
A2
482
521
521
529
22
E
607
607
607
607
3.542e+36
0.0
4.871e+36
0.0
8.413e+36
0.0
23
E
607
617
617
607
3.542e+36
0.0
4.871e+36
0.0
8.413e+36
0.0
24
B1
775
775
775
775
1.211e+39
2.5
9.085e+38
1.9
2.120e+39
4.4
25
B2
779
779
779
779
6.292e+37
0.1
8.651e+37
0.2
1.494e+38
0.3
26
A2
779
779
779
784
27
E
784
784
784
784
2.925e+38
0.6
4.022e+38
0.8
6.948e+38
1.4
28
E
784
784
784
799
2.925e+38
0.6
4.022e+38
0.8
6.948e+38
1.4
29
A1
1079
1079
1079
1079
9.158e+38
1.9
4.873e+38
1.0
1.403e+39
2.9
30
E
1081
1081
1081
1081
1.144e+37
0.0
1.573e+37
0.0
2.718e+37
0.1
31
E
1081
1082
1082
1081
1.144e+37
0.0
1.573e+37
0.0
2.718e+37
0.1
32
B1
1082
1086
1086
1082
1.756e+38
0.4
1.317e+38
0.3
3.074e+38
0.6
33
A2
1086
1127
1127
1127
34
B2
1127
1188
1188
1196
1.471e+36
0.0
2.023e+36
0.0
3.494e+36
0.0
35
E
1196
1196
1196
1196
2.226e+38
0.5
3.061e+38
0.6
5.287e+38
1.1
36
E
1196
1243
1243
1233
2.226e+38
0.5
3.061e+38
0.6
5.287e+38
1.1
No.  Char.  ω TO  ω LOx  ω LOy  ω LOz  I ∥  I ⊥  I Total 

You can define the size of the supercell for the visualization of the vibration.

Nx: 
Ny: 
Nz: 
Normalized
Raw
Options for intensity.