c2x and Spinors
This page serves to give a trivial example of using Castep, c2x and spinors. GaAs is used as an example. From version 2.30 of c2x the same analysis can be performed on the output of Abinit or QE. The text below describes using Castep, but a corresponding input file for QE would be GaAs.in.
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 c2x 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.
(Note a change in Castep's
.check file format
introduced in Castep 18 caused the reading of spinor components
to fail until c2x was modified at version 2.34c.)