-    TOPAZ     -    Al2SiO4F2

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:  62  Pbnm 
Lattice parameters (Å):  4.6499  8.7968  8.3909 
Angles (°):  90.0  90.0  90.0 

Symmetry (theoretical): 

Space group:  62  Pbnm 
Lattice parameters (Å):  4.5849  8.6722  8.2651 
Angles (°):  90.0  90.0  90.0 

Cell contents: 

Number of atoms:  36 
Number of atom types: 
Chemical composition: 

Atomic positions (theoretical):

Al:  0.9039  0.1309  0.0826 
Si:  0.3983  0.9404  0.2500 
O:  0.7939  0.5320  0.2500 
O:  0.4572  0.7551  0.2500 
O:  0.7892  0.0105  0.9087 
F:  0.9022  0.7522  0.0571 
Al:  0.4039  0.3691  0.9174 
Si:  0.8983  0.5596  0.7500 
O:  0.2939  0.9680  0.7500 
O:  0.9572  0.7449  0.7500 
O:  0.2892  0.4895  0.0913 
F:  0.4022  0.7478  0.9429 
Al:  0.0961  0.8691  0.5826 
Si:  0.6017  0.0596  0.7500 
O:  0.2061  0.4680  0.7500 
O:  0.5428  0.2449  0.7500 
O:  0.2108  0.9895  0.4087 
F:  0.0978  0.2478  0.5571 
Al:  0.5961  0.6309  0.4174 
Si:  0.1017  0.4404  0.2500 
O:  0.7061  0.0320  0.2500 
O:  0.0428  0.2551  0.2500 
O:  0.7108  0.5105  0.5913 
F:  0.5978  0.2522  0.4429 
Al:  0.0961  0.8691  0.9174 
O:  0.2108  0.9895  0.0913 
F:  0.0978  0.2478  0.9429 
Al:  0.5961  0.6309  0.0826 
O:  0.7108  0.5105  0.9087 
F:  0.5978  0.2522  0.0571 
Al:  0.9039  0.1309  0.4174 
O:  0.7892  0.0105  0.5913 
F:  0.9022  0.7522  0.4429 
Al:  0.4039  0.3691  0.5826 
O:  0.2892  0.4895  0.4087 
F:  0.4022  0.7478  0.5571 
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: 

Size:

  
Nx:  Ny:  Nz:    
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.
 

Parameters of the Calculation 


All the calculations have been done using the ABINIT software. This is a list of the most representative parameteres used during the Raman calculation.


Number of electronic bands: 26
k-points  
   grid: 4 2 2 
   number of shifts: 
   shifts: 0.5 0.5 0.5 
Kinetic energy cut-off: 40 Ha  [=1088.464 eV ]
eXchange-Correlation functional: LDA pw90 

Pseudopotentials: 
Al:  aluminium, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local 
Si:  silicon, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local 
O:  oxygen, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local 
F:  fluorine, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local