- RINGWOODITE - Mg₂SiO₄

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:	227		Fd-3m
Lattice parameters (Å):	8.0709	8.0709		8.0709
Angles (°):	90.0	90.0		90.0

Symmetry (theoretical):

Space group:	227		Fd-3m
Lattice parameters (Å):	5.6170	5.6170		5.6170
Angles (°):	60.0	60.0		60.0

Cell contents:

Number of atoms:	14
Number of atom types:	3
Chemical composition:	0

Atomic positions (theoretical):

Si:	0.1250	0.1250	0.1250
Si:	0.8750	0.8750	0.8750
Mg:	0.5000	0.5000	0.5000
Mg:	0.5000	0.5000	0.0000
Mg:	0.5000	0.0000	0.5000
Mg:	0.0000	0.5000	0.5000
O:	0.2448	0.2448	0.2448
O:	0.2448	0.2448	0.7657
O:	0.2448	0.7657	0.2448
O:	0.7657	0.2448	0.2448
O:	0.7552	0.7552	0.2343
O:	0.7552	0.7552	0.7552
O:	0.7552	0.2343	0.7552
O:	0.2343	0.7552	0.7552

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	T1u	0	0	0	0
2	T1u	0	0	0	0
3	T1u	0	0	0	0
4	T2u	213	213	213	213
5	T2u	213	213	213	213
6	T2u	213	213	213	213
7	T2g	309	309	309	309	1.972e+37 0.1	2.712e+37 0.1	4.685e+37 0.1
8	T2g	309	309	309	309	2.053e+37 0.1	1.979e+37 0.1	4.032e+37 0.1
9	T2g	309	309	309	309	2.046e+37 0.1	3.358e+37 0.1	5.404e+37 0.1
10	T1g	350	350	350	350
11	T1g	350	350	350	350
12	T1g	350	350	350	350
13	T1u	351	351	351	351
14	T1u	351	351	351	351
15	T1u	351	351	351	351
16	Eu	357	357	357	357
17	Eu	357	357	357	357
18	Eg	377	377	377	377	9.782e+38 2.6	7.337e+38 1.9	1.712e+39 4.5
19	Eg	377	377	377	377	9.782e+38 2.6	7.337e+38 1.9	1.712e+39 4.5
20	T1u	419	419	419	419
21	T1u	419	419	419	419
22	T1u	419	450	450	450
23	T2u	450	450	450	450
24	T2u	450	450	450	450
25	T2u	450	542	542	542
26	T1u	547	547	547	547
27	T1u	547	547	547	547
28	T1u	547	554	554	554
29	Eu	554	554	554	554
30	Eu	554	560	560	560
31	A2u	581	581	581	581
32	T2g	594	594	594	594	6.062e+37 0.2	7.274e+37 0.2	1.334e+38 0.4
33	T2g	594	594	594	594	6.043e+37 0.2	9.014e+37 0.2	1.506e+38 0.4
34	T2g	594	594	594	594	6.062e+37 0.2	8.522e+37 0.2	1.458e+38 0.4
35	T2g	804	804	804	804	5.585e+39 14.8	9.411e+39 25.0	1.500e+40 39.8
36	T2g	804	804	804	804	5.585e+39 14.8	5.541e+39 14.7	1.113e+40 29.5
37	T2g	804	804	804	804	5.585e+39 14.8	8.087e+39 21.5	1.367e+40 36.3
38	A2u	813	813	813	813
39	T1u	816	816	816	816
40	T1u	816	816	816	816
41	T1u	816	829	829	829
42	A1g	829	975	975	975	3.766e+40 100.0	0.000e+0 0.0	3.766e+40 100.0

No.

Char.

ω TO

ω LOx

ω LOy

ω LOz

I ∥

I ⊥