-    OLDHAMITE-NININGERITE SERIES     -    MgCa3S4

This is a term of the MgS-Cas solid solution with ordered super-structure: every 4th Ca atom is replaced by 1 Mg. Because of symmetry, there is no Raman-active mode; all the modes are InfraRed-active. See article for details

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:  221  Pm-3m 
Lattice parameters (Å):       
Angles (°):  90  90  90 

Symmetry (theoretical): 

Space group:  221  Pm-3m 
Lattice parameters (Å):  5.5235  5.5235  5.5235 
Angles (°):  90  90  90 

Cell contents: 

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

Atomic positions (theoretical):

Mg:  0.0000  0.0000  0.0000 
Ca:  0.0000  0.0000  0.0000 
Ca:  0.0000  0.0000  0.0000 
Ca:  0.0000  0.0000  0.0000 
S:  0.0000  0.0000  0.0000 
S:  0.0000  0.0000  0.0000 
S:  0.0000  0.0000  0.0000 
S:  0.0000  0.0000  0.0000 
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.

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
T1u
74
74
74
74
5
T1u
74
74
74
74
6
T1u
74
113
113
113
7
T2u
113
113
113
113
8
T2u
113
113
113
113
9
T2u
113
117
117
117
10
T1u
121
121
121
121
11
T1u
121
121
121
121
12
T1u
121
149
149
149
13
T1u
177
177
177
177
14
T1u
177
177
177
177
15
T1u
177
180
180
180
16
T1u
286
286
286
286
17
T1u
286
286
286
286
18
T1u
286
298
298
298
19
T2u
298
298
298
298
20
T2u
298
298
298
298
21
T2u
298
307
307
307
22
T1u
311
311
311
311
23
T1u
311
311
311
311
24
T1u
311
372
372
372
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.