How to include QED corrections

The following instructions assume familiarity with the main programs of the pCI package.

Steps to run a QED calculation

In this section, we will introduce calculations including QED corrections.

  1. Construct basis set by running hfd and bass to obtain HFD.DAT

  2. Run sgc0 to form an empty SGC.CON file

  3. cp HFD.DAT HFD-noQED.DAT - save a copy of HFD.DAT without QED

  4. Create a file qedpot.inp with number corresponding to the variant of the QED potential and the name of the HFD.DAT file.

    Click here to see a description of qedpot.inp.
    1            # kvar=1-5, Variant of QED potential
HFD.DAT      # name of file holding basis sets

  5. Create a file qed.in selecting options.

    Click here to see a description of qed.in.
    1   # 1 for general diagonalization, 2 for first-order
1   # 1 for no QED, 2 for QED
2   # 0 for Coulomb, 1 for Gaunt, 2 for Full Breit

  6. Loop until convergence:

    • Run qedpot_conf to construct selected QED potential

    • Run qed_rot to rotate orbitals to diagonalize Hamiltonian with QED corrections

  7. cp SGC.CON SGC-noQED.CON - save a copy of SGC.CON without QED

  8. Run qedpot_conf

  9. Rename SGCqed.CON to SGC.CON

  10. Run conf

You can also use the following batch.qed script for steps 3-9, making sure to change inputs relevant to your job.
#! /bin/bash -fe
kvar=1  # variant of QED potential
bin='./'
qedpot=$bin'qedpot_conf'
qedrot=$bin'qed_rot'
iter=25 # max number of iterations
#####################################
cat >qedpot.inp <<EndofFile
 $kvar
 HFD.DAT
EndofFile
#####################################
cat >qed.in <<EndofFile
1   # diagonalization
1   # 1 for noQED, 2 for QED
2   # 0 for Coulomb, 1 for Gaunt, 2 for Full Breit

EndofFile
#####################################
n=1
while [ $n -lt $iter ]; do
echo 'Iteration '$n
$qedpot >qp.res
$qedrot <qed.in >qr.res
grep 'changed' "QED_ROT.RES"
  if grep -q reached "QED_ROT.RES"; then
  echo 'Converged in '$n' iterations'
  break
  fi
  let n=n+1
done
cp SGC.CON SCG-noQED.CON
./qedpot_conf >qp.res
cp SGCqed.CON SGC.CON
#####################################