The DOS 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: Density of states

After you have completed the groundstate run and have obtained the corresponding total energy, you can go for more properties of the system. One of the most fundamental ones is the density of states (DOS). The DOS gives you information on the energy levels in your system, or — more precisely — about how many electronic states there are at any given energy.

To calculate it, you need to do the following simple modifications in input.xml (for more details, see Input Reference):

1. add the attribute do="skip" to the xml-element groundstate;
2. add the element properties after the groundstate element;
3. insert the subelement dos into the element properties;
4. add the attribute nsmdos="1" to the element dos.

The corresponding part of the input.xml should now look like this:

  ...
    <groundstate ngridk="8  8  8" do="skip">
    </groundstate>
 
    <properties>
        <dos nsmdos="1">
        </dos>
    </properties>
  ...

Then execute excitingser again on the command line:

$ excitingser

This time, the program will produce the following files:

filename description TDOS.OUT total DOS PDOS_S01_A0001.OUT partial density of states for each atom, l and m quantum number. IDOS.OUT interstitial DOS dos.xml all densities of states assembled in XML format.

To visualize the DOS, execute

$ xsltproc $EXCITINGVISUAL/xmldos2grace.xsl dos.xml > Ag_dos.agr

This produces the file Ag_dos.agr for xmgrace. Open it with the command

$ xmgrace Ag_dos.agr

This will open the plotting tool xmgrace and display the total and partial densities of states. The units in this plot are

• Energy (Hartree) for the x axis
• DOS (states/unit cell/Hartree) for the y axis.

Please note: In the DOS plots, energies are relative to the Fermi energy, i.e., E_F=0 Ha.

You can use xmgrace to change the plot appearance in any way you want, zoom in to see details of the DOS, or produce a figure in any format you like (ps, jpg, png, etc. …).

The DOS plot, by default, contains a partial DOS for any quantum number m and l, in this case up to l=4, i.e., up to the f states. Since the figure is crowded with this information, and in silver no f states are present, it is convenient to hide the latter.