How to use the PWTK package for multiple calculations

To download and install the PWTK package click on the following link:

How to download and install PWTK package

PWTK allows (re)assigning namelist variables or the content of cards on the fly, which is useful when performing multiple calculations, where only a few parameters per calculation change.

We need 2 files: scf.si.in and si_pbe_v1.uspp.F.UPF

scf.si.in

&CONTROL
  calculation = 'scf'
       outdir = 'Si_example/'
   pseudo_dir = './'
 /

 &SYSTEM
        ibrav = 2
    celldm(1) = 10.2
          nat = 2
         ntyp = 1
      ecutwfc = 18.0
      ecutrho = 72.0
 /

 &ELECTRONS
     conv_thr = 1d-7
 /

ATOMIC_SPECIES
   Si  1.00  si_pbe_v1.uspp.F.UPF 

ATOMIC_POSITIONS alat 
   Si    0.00  0.00  0.00    
   Si    0.25  0.25  0.25    

K_POINTS automatic 
   4 4 4   1 1 1

As an example, let us perform a few tests on Si bulk. To this end, we will use the above scf.si.in input file. Below is the PWTK script that scans the energy cutoff (ecutwfc), k-point mesh (K_POINTS), and lattice parameter (celldm(1)):

# the "load_fromPWI" command loads the pw.x input file
load_fromPWI scf.si.in

#------------------------
# scan the energy-cuttofs
#------------------------
# the "scanpar" command loops over a parameter; it is similar to a
# one-parameter Tcl "foreach" command

scanpar e {10.0 14.0 18.0 22.0} {
   # load the new energy cuttofs
   SYSTEM "ecutwfc = $e, ecutrho = 4*$e"

   # perform the pw.x calculation (I/O files: scf.Si_e$e.in & scf.Si_e$e.out)
   runPW scf.Si_e$e

   # store $e and total energy in the 'ecut.dat' file 
   write ecut.dat [pwo_totene scf.Si_e$e.out]
}
# plot the result
plot -xl "ecutwfc (Ry)" -yl "Total energy (Ry)" ecut.dat


# let's perform below scans at ecutwfc = 18.0 Ry 
SYSTEM "ecutwfc = 18.0, ecutrho = 4*18.0"

#-----------------
# scan the kpoints
#-----------------

scanpar k {2 4 6} {
   # load new k-points
   K_POINTS automatic "$k $k $k   1 1 1"

   # perform the pw.x calculation (I/O files: scf.Si_k$k.in & scf.Si_k$k.out)
   runPW scf.Si_k$k

   # store $k and total energy into the 'k.dat' file 
   write k.dat [pwo_totene scf.Si_k$k.out]
}
# plot the result
plot -xl "K of the (KxKxK) k-point mesh" -yl "Total energy (Ry)" k.dat


#---------------------------
# scan the lattice-parameter
#---------------------------
# let's perform this scan at the 6x6x6 k-mesh
K_POINTS automatic "6 6 6   1 1 1"

# here we use the "seq" command, which behaves just like the Unix "seq" command
foreach a [seq 9.2 0.2 10.8] {
   # load new celldm(1)
   SYSTEM " celldm(1) = $a "

   # perform the calculation (I/O files: scf.Si_alat$a.in & scf.Si_alat$a.out)
   runPW scf.Si_alat$a

   # store $a and total energy into the 'alat.dat' file
   write alat.dat [pwo_totene scf.Si_alat$a.out]
}
# plot the result
plot -xl "A lattice paramater (bohr)" -yl "Total energy (Ry)" alat.dat

Let us store this script into the scan.pwtk file. The script is run from the terminal by executing: