- MAGNESITE - MgCO₃

Theoretical atomic positions and lattice parameters at experimental volum from 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):	4.6339	4.6339		15.0177
Angles (°):	90	90		120

Symmetry (theoretical):

Space group:	167		R-3c
Lattice parameters (Å):	5.6637	5.6637		5.6637
Angles (°):	48.38	48.38		48.38

Cell contents:

Number of atoms:	10
Number of atom types:	3
Chemical composition:	0

Atomic positions (theoretical):

Mg:	0.0000	0.0000	0.0000
C:	0.2500	0.2500	0.2500
O:	0.5257	0.9743	0.2500
O:	0.9743	0.2500	0.5257
Mg:	0.5000	0.5000	0.5000
C:	0.7500	0.7500	0.7500
O:	0.7500	0.4743	0.0257
O:	0.2500	0.5257	0.9743
O:	0.4743	0.0257	0.7500
O:	0.0257	0.7500	0.4743

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	Eg	204	204	204	204	6.473e+38 0.7	9.106e+38 1.0	1.558e+39 1.7
5	Eg	204	204	204	204	6.473e+38 0.7	9.321e+38 1.0	1.579e+39 1.7
6	Eu	227	227	227	227
7	Eu	227	230	230	227
8	A2u	230	235	235	271
9	A2g	292	292	292	292
10	Eu	292	292	292	292
11	Eu	292	296	296	292
12	Eg	314	314	314	314	8.918e+39 9.6	1.484e+40 16.0	2.376e+40 25.6
13	Eg	314	314	314	314	8.917e+39 9.6	1.019e+40 11.0	1.910e+40 20.6
14	A2g	342	342	342	342
15	Eu	342	342	342	342
16	Eu	342	347	347	342
17	A2u	347	358	358	358
18	A1u	358	462	462	445
19	Eg	720	720	720	720	3.027e+39 3.3	4.573e+39 4.9	7.600e+39 8.2
20	Eg	720	720	720	720	3.027e+39 3.3	2.362e+39 2.5	5.389e+39 5.8
21	Eu	726	726	726	726
22	Eu	726	729	729	726
23	A2u	848	848	848	857
24	A2g	857	857	857	877
25	A1g	1087	1087	1087	1087	9.019e+40 97.2	2.612e+39 2.8	9.281e+40 100.0
26	A1u	1089	1089	1089	1089
27	Eu	1422	1422	1422	1422
28	Eu	1422	1440	1440	1422
29	Eg	1440	1440	1440	1440	1.258e+39 1.4	1.613e+39 1.7	2.872e+39 3.1
30	Eg	1440	1583	1583	1440	1.258e+39 1.4	1.120e+39 1.2	2.378e+39 2.6

No.

Char.

ω TO

ω LOx

ω LOy

ω LOz

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I ⊥