In this tutorial, we will present how to determine the magnetic ground state of the Chromium compound Cr. We will do a volume optimization of the 2 magnetic states FM and AFM of Cr in its crystal structure BCC.

We need 2 input files and 2 scripts.

Input files

Cr-mag.cell

%BLOCK LATTICE_ABC
2.88 2.88 2.88
90 90 90
%ENDBLOCK LATTICE_ABC

%BLOCK POSITIONS_FRAC
Cr    0.0  0.0 0.0  spin=2.0
#Cr    0.5  0.5 0.5  spin=2.0
#Cr    0.5  0.5 0.5  spin=-2.0  
%ENDBLOCK POSITIONS_FRAC

kpoint_mp_spacing 0.04

symmetry_generate

 

Cr-mag.param

task     SinglePoint          ! The TASK keyword instructs CASTEP what to do
xc_functional   PBE           ! Which exchange-correlation functional to use.
cut_off_energy  500 eV        !
opt_strategy    speed         ! Choose algorithms for best speed
spin_polarized : true 
nextra_bands : 18

 

Scripts

You may download the scripts  generate_EV-mag.sh and  plot_EV-mag.sh from the following links: 

$ wget https://raw.githubusercontent.com/jazairdz/Castep/refs/heads/main/generate_EV-mag.sh
$ wget https://raw.githubusercontent.com/jazairdz/Castep/refs/heads/main/plot_EV-mag.sh

 

Creating input files of FM and AFM states

$ cp Cr-mag.cell Cr-fm.cell

Uncheck the following line

Cr    0.5  0.5 0.5   spin=2.0
 
$ cp Cr-mag.cell Cr-afm.cell 

Uncheck the following line

Cr    0.5  0.5 0.5   spin=-2.0

$ cp Cr-mag.param Cr-fm.param
$ cp Cr-mag.param Cr-afm.param

 

Execution

$ sh generate_EV-mag.sh

$ sh plot_EV-mag.sh
 
We get the following plot

We see from the plot that the AFM state is the magnetic ground state.