- 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):	4.6330	4.6330		15.0200
Angles (°):	90	90		120

Symmetry (theoretical):

Space group:	167		R-3c
Lattice parameters (Å):	5.6667	5.6667		5.6667
Angles (°):	49.03	49.03		49.03

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:	0.5260	0.9740	0.2500
O:	0.9740	0.2500	0.5260
Mg:	0.5000	0.5000	0.5000
C:	0.7500	0.7500	0.7500
O:	0.7500	0.4740	0.0260
O:	0.2500	0.5260	0.9740
O:	0.4740	0.0260	0.7500
O:	0.0260	0.7500	0.4740

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	A2u	202	202	202	202	5.370e+38 0.6	6.490e+38 0.7	1.186e+39 1.3
5	Eu	202	202	202	202	5.370e+38 0.6	8.748e+38 0.9	1.412e+39 1.5
6	Eu	229	229	229	229
7	Eg	229	232	232	229
8	Eg	232	237	237	273
9	A2g	287	287	287	287
10	Eu	287	290	290	287
11	Eu	293	293	293	293
12	Eg	312	312	312	312	9.122e+39 9.7	1.423e+40 15.2	2.335e+40 24.9
13	Eg	312	312	312	312	9.122e+39 9.7	1.135e+40 12.1	2.047e+40 21.9
14	A1u	335	335	335	335
15	A2g	335	339	339	335
16	Eu	339	339	339	339
17	Eu	339	355	355	355
18	A2u	355	459	459	440
19	Eg	719	719	719	719	3.057e+39 3.3	3.773e+39 4.0	6.830e+39 7.3
20	Eg	719	719	719	719	3.057e+39 3.3	3.244e+39 3.5	6.302e+39 6.7
21	Eu	725	725	725	725
22	Eu	725	728	728	725
23	A2u	848	848	848	857
24	A2g	857	857	857	877
25	A1g	1085	1085	1085	1085	9.106e+40 97.2	2.607e+39 2.8	9.367e+40 100.0
26	A1u	1087	1087	1087	1087
27	Eu	1419	1419	1419	1419
28	Eu	1419	1436	1436	1419
29	Eg	1436	1436	1436	1436	1.341e+39 1.4	1.882e+39 2.0	3.223e+39 3.4
30	Eg	1436	1580	1580	1436	1.341e+39 1.4	1.008e+39 1.1	2.349e+39 2.5

No.

Char.

ω TO

ω LOx

ω LOy

ω LOz

I ∥

I ⊥