LiF BSE/TDDFT (OBSOLETE!)

Excited states for Lithium Fluoride

We will calculate the dielectric function of LiF by two different approaches, i.e. via the BSE formalism and then TDDFT utilizing the BSE-derived kernel.

The first step: BSE

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="inputtohtml.xsl" type="text/xsl"?>
 
<input xsi:noNamespaceSchemaLocation="../../xml/excitinginput.xsd"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsltpath="../../../xml/">
 
  <title>Lithium Fluoride, BSE and TDDFT spectrum</title>
 
  <structure speciespath="../../species">
    <crystal>
      <basevect>3.80402 3.80402 0.00000</basevect>
      <basevect>3.80402 0.00000 3.80402</basevect>
      <basevect>0.00000 3.80402 3.80402</basevect>
    </crystal>
    <species speciesfile="Li.xml">
      <atom coord="0.0000  0.0000  0.0000" bfcmt="0.0 0.0 0.0" />
    </species>
    <species speciesfile="F.xml">
      <atom coord="0.5000  0.5000  0.5000" bfcmt="0.0 0.0 0.0" />
    </species>
  </structure>
 
  <groundstate lradstep="2" lmaxvr="8" ngridk="4  4  4" vkloff="0.05 0.15 0.25">
      <solver evaltol="1e-300" type="Lapack" />
  </groundstate>
 
  <!-- Here are the excited-states parameters, defined in the "xs"-element-->
  <!-- Once the screening is calculated, use the run="skip" attribute for the
   "screening" element -->
  <!-- scissors correction 5.7eV = 0.20947H -->
  <xs xstype="BSE" nosym="true" ngridq="4 4 4" ngridk="4 4 4"
      vkloff="0.05 0.15 0.25" nempty="3" lmaxapwwf="3"
      lmaxemat="3" gqmax="3" broad="0.0073499"
      tevout="true" scissor="0.20947">
      <dosWindow intv="0.0 1.0" points="1200" ></dosWindow>
      <screening screentype="full" nempty="115" />
      <tddft fxctype="MB1" aresdf="false" aresfxc="false" />
      <BSE bsetype="singlet" nstlbse="5 4" />
      <qpointset>
          <qpoint>0.0 0.0 0.0</qpoint>
      </qpointset>    
  </xs>
</input>

The xmgrace graphics can be generated as follows

xsltproc EPSILON_to_xmgrace.xsl EPSILON_NAR_BSEsinglet_SCRfull_OC11.OUT.xml > EPSILON_NAR_BSEsinglet_SCRfull_OC11.OUT.xml.agr

and is viewed by invoking the command:

xmgrace EPSILON_NAR_BSEsinglet_SCRfull_OC11.OUT.xml.agr

The second step: TDDFT using the BSE-derived xc kernel

Since we do not need to calculate the groundstate again, we add the "do" attribute setting it to "skip":

  <groundstate do="skip" ...

In order to perform a TDDFT calculation we change the "xstype" attribute to "TDDFT":

  <xs xstype="TDDFT"  ...

A hint for the impatient users: The calculation of the screening can be skipped since it has already been performed for the BSE.
Simply set the "run" attribute to "skip" inside the "screening" element.

  <screening run="skip" ...

We again generate an xmgrace graphics:

xsltproc EPSILON_to_xmgrace.xsl EPSILON_NAR_FXC08_OC11_QMT001.OUT.xml > EPSILON_NAR_FXC08_OC11_QMT001.OUT.xml.agr

Results which are converged with respect to the k-point set are given here for comparison: LifResultsConverged