The Band Structure calculation of the silver (Lithium version)

 

Units in exciting

By default, all quantities in the exciting code are given in atomic units: Energies in Hartree, lengths in Bohr, etc. (see Input Reference). In case other units are desirable, they can be converted using templates as a post-processing to exciting's standard output.

 1. Electronic structure of silver: Groundstate calculation

 

To prepare your calculation, create a new, empty directory named Ag somewhere on your filesystem. In this directory, save the following lines as input.xml.

<input>
 
  <title>Ag</title>
 
  <structure speciespath="$EXCITINGROOT/species">
    <crystal scale="7.7201">
      <basevect>0.5 0.5 0.0</basevect>
      <basevect>0.5 0.0 0.5</basevect>
      <basevect>0.0 0.5 0.5</basevect>
    </crystal>
    <species speciesfile="Ag.xml" chemicalSymbol="Ag">
      <atom coord="0.0  0.0  0.0" />
    </species>
  </structure>
 
  <groundstate ngridk="8  8  8"></groundstate>
 
</input>

N.B.: Do not forget to replace in the input.xml the string "$EXCITINGROOT" by the actual value of the environment variable $EXCITINGROOT using the command

$ SETUP-excitingroot.sh

If the visualization program XCrySDen is set up appropriately (find here how to do this: XCrySDen Setup for exciting) you can visualize the structure in the exciting input file executing

$ xcrysden --exciting input.xml

After this, start the groundstate calculation by executing the following command in the Ag directory:

$ excitingser

The calculation should roughly take 1 minute. During the calculation, output files are created, which contain all kind of information on your material system and on the calculation. Some of the output files are already created at the beginning of the calculation and will not be changed anymore during the run. 

2. Electronic structure of silver: Band structure

 

Now we are ready for a more detailed view on the electronic structure: The band structure. In addition to the energy of each state, the band structure shows the dependence of the energy eigenvalues on the coordinates in k-space.

To calculate the band structure of silver, insert the subelement bandstructure in the element properties with the following specifications:

...
   <properties>
 
      <bandstructure>
         <plot1d>
            <path steps="100">
               <point coord="0.750   0.500   0.250" label="W"    ></point>
               <point coord="0.500   0.500   0.500" label="L"    ></point>
               <point coord="0.000   0.000   0.000" label="GAMMA"></point>
               <point coord="0.500   0.500   0.000" label="X"    ></point>
               <point coord="0.750   0.500   0.250" label="W"    ></point>
               <point coord="0.750   0.375   0.375" label="K"    ></point>
            </path>
         </plot1d>
      </bandstructure>
 
   </properties>
...

As you may have realized, we have removed the subelement dos now.

Now execute excitingser again on the command line:

$ excitingser

This makes the code produce the band structure, which is written to bandstructure.xml. To visualize the band structure, execute the following command:

$ xsltproc $EXCITINGVISUAL/xmlband2agr.xsl bandstructure.xml

Now you have produced the xmgrace file Ag_bandstructure.agr, which you can open, visualize and manipulate with xmgrace:

$ xmgrace Ag_bandstructure.agr

The result should look like this: