Ferromagnetic calculation of the bcc Fe (Lithium version)

 Ferromagnetic calculation is a spin-polarized calculation which, is done in a second-variational scheme. This means that at each iteration of the selfconsistency, the non-magnetic equations are solved (first-variational scheme). Eigenfunctions obtained in this way are not the final solutions, but being close to them, they are used as a basis set for expanding the final wavefunctions to construct spinors in the second-variational scheme. 

Creating an input file

An input file for spin-polarized calculations contains the basic elements and attributes discussed in previous tutorials. In addition, exciting requires for these calculations to start with a magnetic atomic configuration by using an external field, bfieldc. This attribute is added to the subelement spin which is included in the element groundstate. In this example, the initial external field is parallel to the z axis and has a magnitude of 0.5.

  ...
  <groundstate ...>
    <spin bfieldc="0.0 0.0 0.5">
  ...

This external field bfieldc either vanishes during the self-consistent calculation or through an extra fictitious external magnetic contribution. This is added to the result via the attribute reducebf that damps the initial external magnetic field. For instance, in the following example, the choice reducebf=0.5 means that at every new iteration the external magnetic field will be reduced by half.

  ...
  <groundstate ...>
    <spin bfieldc="0.0 0.0 0.5"
          reducebf="0.5"
          spinorb="true">
    </spin>
  </groundstate>
  ...

The last attributes spinorb="true" is required for including spin-orbit coupling.

Furthermore, in order to decompose the magnetic moments into spin and orbital contributions, the element LSJ (notice that the xml input file is case sensitive!) must be given as a subelement of the now required element properties.

  ...
  <properties>
    <LSJ/>
  </properties>
  ...

A complete input file for a specific calculation will be given in Section 2.

How output files look like

The Cartesian components of the total magnetic moment per unit cell are written in the file MOMENT.OUT. An example for this file is shown here

...
 -0.6752316193E-20  0.1179704690E-19  -2.293664741

Similar informations are also contained in the file INFO.OUT, where the decomposition of the magnetic moment per atom, in the muffin-tin spheres, and in the interstitial space is also saved.

...
Moments :
 interstitial                :  -0.8860331678E-20  0.1232139874E-19  0.4445389422E-01
 muffin-tins
  species :    1 (Fe)
        atom    1                   :   0.2108015485E-20 -0.5243518432E-21  -2.338118635    
 total in muffin-tins        :   0.2108015485E-20 -0.5243518432E-21  -2.338118635    
 total moment                :  -0.6752316193E-20  0.1179704690E-19  -2.293664741    
...

The expectation value of the Cartesian components of L, S, and J=L+S are printed in the output file LSJ.OUT. Notice that these values should be multiplied by 2 to get the total value of the components of the orbital, spin, and total moment, respectively.

Expectation values are computed only over the muffin-tin

Species :    1 ()
 atom :    1
  L :  -0.5571546298E-19  0.2325110800E-17 -0.4724817308E-01
  S :  -0.1138754100E-18  0.2325908361E-19  -1.169575317    
  J :  -0.1695908730E-18  0.2348369884E-17  -1.216823490

 

Here, copy and paste the following input to which the element spin has been added.

<input>
 
  <title>FM bcc Fe</title>
 
  <structure  speciespath="$EXCITINGROOT/species/">
    <crystal scale="5.416">
      <basevect> 0.5     0.5    -0.5 </basevect>
      <basevect> 0.5    -0.5     0.5 </basevect>
      <basevect>-0.5     0.5     0.5 </basevect>
    </crystal>
    <species speciesfile="Fe.xml" rmt="2.3">
      <atom coord="0.00 0.00 0.00"/>
    </species>
  </structure>
 
  <groundstate ngridk="10 10 10"
               xctype="GGAPerdew-Burke-Ernzerhof"
               stype= "Methfessel-Paxton 1"
               swidth="0.01"
               rgkmax="7.0"
               nempty="5">
    <spin bfieldc="0.0 0.0 0.5"
          reducebf="0.5"
          spinorb="false">
    </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.

You can now run again exciting.

$ excitingser

Notice that in the file input.xml which is shown above, we added the calculation of the density of states inside the element properties. To visualize the density of states use the command lines

$ xsltproc --stringparam ID "t///" $EXCITINGVISUAL/xmldos2grace.xsl dos.xml > tdos.agr
$ xmgrace tdos.agr

The plot you obain is should be similar to this.