-    MAGNESITE     -    MgCO3

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:  167  R-3c 
Lattice parameters (Å):  4.6330  4.6330  15.0200 
Angles (°):  90.0  90.0  120.0 

Symmetry (theoretical): 

Space group:  167  R-3c 
Lattice parameters (Å):  5.5158  5.5158  5.5158 
Angles (°):  46.7  46.7  46.7 

Cell contents: 

Number of atoms:  10 
Number of atom types: 
Chemical composition: 

Atomic positions (theoretical):

Mg:  0.0000  0.0000  0.0000 
C:  0.2500  0.2500  0.2500 
O:  0.5286  0.9714  0.2500 
O:  0.9714  0.2500  0.5286 
Mg:  0.5000  0.5000  0.5000 
C:  0.7500  0.7500  0.7500 
O:  0.7500  0.4714  0.0286 
O:  0.2500  0.5286  0.9714 
O:  0.4714  0.0286  0.7500 
O:  0.0286  0.7500  0.4714 
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.
     

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.

Horizontal:
Xmin:
Xmax:
Vertical:
Ymin:
Ymax:
 
Choose the polarization of the lasers.
I ∥ 
I ⊥ 
I Total 

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
A2u
227
227
227
227
7.882e+38
0.8
1.281e+39
1.3
2.070e+39
2.1
5
Eu
227
227
227
227
7.882e+38
0.8
9.880e+38
1.0
1.776e+39
1.8
6
Eu
231
231
231
231
7
Eg
231
237
237
231
8
Eg
237
242
242
283
9
A2g
317
317
317
317
10
Eu
327
327
327
327
11
Eu
327
333
333
327
12
Eg
346
346
346
346
7.716e+39
7.8
1.107e+40
11.2
1.879e+40
19.0
13
Eg
346
346
346
346
7.716e+39
7.8
1.072e+40
10.8
1.844e+40
18.7
14
A1u
379
379
379
379
15
A2g
383
383
383
383
16
Eu
390
390
390
390
17
Eu
390
400
400
390
18
A2u
400
496
496
482
19
Eg
733
733
733
733
3.587e+39
3.6
5.413e+39
5.5
9.000e+39
9.1
20
Eg
733
733
733
733
3.587e+39
3.6
2.798e+39
2.8
6.385e+39
6.5
21
Eu
742
742
742
742
22
Eu
742
747
747
742
23
A2u
846
846
846
856
24
A2g
856
856
856
881
25
A1g
1105
1105
1105
1105
9.620e+40
97.3
2.632e+39
2.7
9.884e+40
100.0
26
A1u
1107
1107
1107
1107
27
Eu
1447
1447
1447
1447
28
Eu
1447
1466
1466
1447
29
Eg
1466
1466
1466
1466
1.008e+39
1.0
8.455e+38
0.9
1.854e+39
1.9
30
Eg
1466
1612
1612
1466
1.008e+39
1.0
1.407e+39
1.4
2.415e+39
2.4
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.