TCM
UoC crest

Check2xsf and Spinors

This page serves to give a trivial example of using Castep, check2xsf and spinors. GaAs is used as an example.

For the .cell file, the following suffices:

%block LATTICE_CART
ang
 2.8268500  2.8268500  0.0000000
 2.8268500  0.0000000  2.8268500
 0.0000000  2.8268500  2.8268500
%endblock LATTICE_CART

%block POSITIONS_FRAC
 Ga  0.000000000  0.000000000  0.000000000
 As  0.250000000  0.250000000  0.250000000
%endblock POSITIONS_FRAC

%block SPECIES_POT
As  Asrel.RRKJ3.UPF
Ga  Garel.RRKJ3.UPF
%endblock SPECIES_POT

KPOINT_MP_GRID 2 2 2
KPOINT_MP_OFFSET 0.0 0.0 0.0

and for the .param file:

xc_functional   LDA
spin_treatment VECTOR
spin_orbit_coupling true
fix_occupancy   false
popn_calculate  false

One has to provide suitable pseudopotentials, for the OTF ones currently won't do. So they are provided here as Asrel.RRKJ3.UPF and Garel.RRKJ3.UPF. And that is it: one should then be able to run "castep GaAs". The .castep file should say "treating system as non-collinear spin".

Finally, a simple example of check2xsf interpreting the final output:

$ c2x -B=3 -v --null GaAs.check 
Castep version 16.110
Wavefunction grid     24 24 24
Cell volume 45.179174
natoms      2
Requested cut-off energy 408.171 eV
First FFT grid     24 24 24
spins=1   spinors=2
Found 3D data for band_vs0_k1_b3
  min=2.70772e-05  max=0.108625  sum=158.081  int=0.516635
Found 3D data for band_vs1_k1_b3
  min=2.56075e-05  max=0.101641  sum=147.901  int=0.483365

(Extract, as density, band number three, k-point 1 (implicit, modify with -k=), both spinor components (implict, modify with -S=), produce no output other than the above information about extrema and integrals.) Note that the sum of the two integrals is 1.0 exactly as norm-conserving pseudopotentials were used.