- MAGNESITE - MgCO₃

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:	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):	5.5291	5.5291		5.5291
Angles (°):	49.01	49.01		49.01

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:	0.5280	0.9720	0.2500
O:	0.9720	0.2500	0.5280
Mg:	0.5000	0.5000	0.5000
C:	0.7500	0.7500	0.7500
O:	0.7500	0.4720	0.0280
O:	0.2500	0.5280	0.9720
O:	0.4720	0.0280	0.7500
O:	0.0280	0.7500	0.4720

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.

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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	226	226	226	226	8.646e+38 0.9	1.274e+39 1.3	2.139e+39 2.2
5	Eg	226	226	226	226	8.645e+38 0.9	1.214e+39 1.3	2.079e+39 2.1
6	Eu	228	228	228	228
7	Eu	228	234	234	228
8	A2u	234	240	240	279
9	A2g	313	313	313	313
10	Eu	327	327	327	327
11	Eu	327	334	334	327
12	Eg	345	345	345	345	7.658e+39 7.9	1.172e+40 12.1	1.938e+40 20.0
13	Eg	345	345	345	345	7.658e+39 7.9	9.880e+39 10.2	1.754e+40 18.1
14	A2g	377	377	377	377
15	A1u	383	383	383	383
16	Eu	391	391	391	391
17	Eu	391	401	401	391
18	A2u	401	496	496	483
19	Eg	733	733	733	733	3.478e+39 3.6	5.080e+39 5.2	8.558e+39 8.8
20	Eg	733	733	733	733	3.478e+39 3.6	2.870e+39 3.0	6.348e+39 6.5
21	Eu	741	741	741	741
22	Eu	741	746	746	741
23	A2u	847	847	847	856
24	A2g	856	856	856	881
25	A1g	1105	1105	1105	1105	9.449e+40 97.3	2.631e+39 2.7	9.712e+40 100.0
26	A1u	1107	1107	1107	1107
27	Eu	1448	1448	1448	1448
28	Eu	1448	1467	1467	1448
29	Eg	1467	1467	1467	1467	9.769e+38 1.0	8.750e+38 0.9	1.852e+39 1.9
30	Eg	1467	1612	1612	1467	9.769e+38 1.0	1.319e+39 1.4	2.296e+39 2.4

No.

Char.

ω TO

ω LOx

ω LOy

ω LOz

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