-    PLAGIOCLASE     -    (Na,Ca)(Si,Al)4O8

LABRADORITE - Theoretical structure, term in the plagioclase series treated as ideal solid solution using alchemical pseudopotentials. 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:  P-1 
Lattice parameters (Å):  7.599  7.533  6.081 
Angles (°):  106.12  101.66  114.92 

Symmetry (theoretical): 

Space group:  P-1 
Lattice parameters (Å):  7.6471  7.4941  7.0250 
Angles (°):    105.5  101.9 

Cell contents: 

Number of atoms:  26 
Number of atom types: 
Chemical composition: 

Atomic positions (theoretical):

Na:  0.2513  0.2807  0.1133 
Si:  0.8375  0.1723  0.2196 
Si:  0.1880  0.8234  0.2286 
Si:  0.5692  0.7966  0.3253 
Si:  0.8082  0.5726  0.3532 
O:  0.8669  0.1282  0.9871 
O:  0.5930  0.5808  0.2794 
O:  0.6954  0.9275  0.1989 
O:  0.9590  0.6857  0.2349 
O:  0.7333  0.3183  0.2783 
O:  0.3174  0.6943  0.2204 
O:  0.0785  0.2945  0.3867 
O:  0.3316  0.0605  0.4209 
Na:  0.7487  0.7193  0.8867 
Si:  0.1625  0.8277  0.7804 
Si:  0.8120  0.1766  0.7714 
Si:  0.4308  0.2034  0.6747 
Si:  0.1918  0.4274  0.6468 
O:  0.1331  0.8718  0.0129 
O:  0.4070  0.4192  0.7206 
O:  0.3046  0.0725  0.8011 
O:  0.0410  0.3143  0.7651 
O:  0.2667  0.6817  0.7217 
O:  0.6826  0.3057  0.7796 
O:  0.9215  0.7055  0.6133 
O:  0.6684  0.9395  0.5791 
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 4 4 
   number of shifts: 
   shifts: 0.5 0.5 0.5 
Kinetic energy cut-off: 38 Ha  [=1034.0408 eV ]
eXchange-Correlation functional: LDA pw90 

Pseudopotentials: 
Na:  sodium, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local  
Ca:  silicon, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local 
Al:  oxygen, fhi98PP : Trouiller-Martins-type, LDA Ceperley/Alder Perdew/Wang (1992), l= 2 local