- OLDHAMITE-NININGERITE SERIES - Mg₃CaS₄

This is a term of the MgS-Cas solid solution with ordered super-structure: every 4th Mg atom is replaced by 1 Ca. 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):	5.2787	5.2787		5.2787
Angles (°):	90	90		90

Cell contents:

Number of atoms:	8
Number of atom types:	3
Chemical composition:	0

Atomic positions (theoretical):

Ca:	0.0000	0.0000	0.0000
Mg:	0.0000	0.0000	0.0000
Mg:	0.0000	0.0000	0.0000
Mg:	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:

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	112	112	112	112
5	T1u	112	112	112	112
6	T1u	112	112	112	112
7	T2u	121	121	121	121
8	T2u	121	121	121	121
9	T2u	121	121	121	121
10	T1u	173	173	173	173
11	T1u	173	173	173	173
12	T1u	173	173	173	173
13	T1u	191	191	191	191
14	T1u	191	191	191	191
15	T1u	191	202	202	202
16	T2u	202	202	202	202
17	T2u	202	202	202	202
18	T2u	202	235	235	235
19	T1u	235	235	235	235
20	T1u	235	235	235	235
21	T1u	235	318	318	318
22	T1u	395	395	395	395
23	T1u	395	395	395	395
24	T1u	395	426	426	426

No.

Char.

ω TO

ω LOx

ω LOy

ω LOz

I ∥

I ⊥