Antiferromagnetic calculation of bcc Cr ( Lithium version)

 

For an anti-ferromagnetic calculation, the only major change with respect to the ferromagnetic one is that the spin axis for each atom has to be specified. In exciting this is done by setting the attribute bfcmt of the element atom.

    ...
    <species speciesfile="Cr.xml">
      <atom coord="0.00 0.00 0.00" bfcmt="0.0  0.0  1.7"/>
      <atom coord="0.50 0.50 0.50" bfcmt="0.0  0.0 -1.7"/>
    </species>
    ...

To simulate the anti-ferromagnetic ordering for Cr in the bcc phase, we have to choose a unit cell which is twice as large the primitive cell of the bcc lattice and, therefore, contains two Cr atoms (do you know why?). The corresponding input file (input.xml) can be found in To-Do/AFM/step0.

<input>
 
  <title>AFM bcc Cr</title>
 
  <structure  speciespath="$EXCITINGROOT/species/">
    <crystal scale="5.4424">
      <basevect> 1.0     0.0     0.0 </basevect>
      <basevect> 0.0     1.0     0.0 </basevect>
      <basevect> 0.0     0.0     1.0 </basevect>
    </crystal>
    <species speciesfile="Cr.xml">
      <atom coord="0.00 0.00 0.00" bfcmt="0.0  0.0  1.7"/>
      <atom coord="0.50 0.50 0.50" bfcmt="0.0  0.0 -1.7"/>
    </species>
  </structure>
 
  <groundstate ngridk="8 8 8"
               xctype="GGAPerdew-Burke-Ernzerhof"
               stype= "Methfessel-Paxton 1"
               swidth="0.05"
               rgkmax="6.0"
               nempty="5"
               maxscl="20"
               vkloff="0.5  0.5  0.5">
    <spin bfieldc="0.0 0.0 1.0"
          reducebf="0.5"
          spinorb="true">
    </spin>
  </groundstate>
 
  <properties>
    <dos nsmdos="0" winddos="-0.3 0.3" />
    <LSJ/>
  </properties>
 
</input>

Also in this case, do not forget to replace in the input.xml the string "$EXCITINGROOT" by the actual value of the environment variable $EXCITINGROOT.

Now, run exciting.

$ excitingser

As we have seen before, the resulting total moment per unit cell is written in the output file MOMENT.OUT. In this case, obviously, the value should be very close to zero for anti-ferromagnetic systems. The result for the magnetic moment per atom can be found at the bottom of the file INFO.OUT.