This tutorial can be downloaded link.

1.0 Getting Started: GW calculation

In order to compute the GW electronic structure of the silane molecule you need to run pw.x, wstat.x and wfreq.x in sequence.

Step 1: Ground State

The ground state electronic structure of silane molecule with QuantumEspresso is obtained by running pw.x. The pseudopotential files for Si and H in UPF format can be downloaded from: QE-PP database, or from SG15 database. Check out the pw.x input description in order to generate an input file for QuantumEspresso called pw.in.

Download these files in your current working directory:

%%bash
wget -N -q http://www.west-code.org/doc/training/silane/pw.in
wget -N -q http://www.quantum-simulation.org/potentials/sg15_oncv/upf/H_ONCV_PBE-1.0.upf
wget -N -q http://www.quantum-simulation.org/potentials/sg15_oncv/upf/Si_ONCV_PBE-1.1.upf

Let’s inspect the pw.in file, input for pw.x.

%%bash
cat pw.in

&control
calculation  = 'scf'
restart_mode = 'from_scratch'
pseudo_dir   = './'
outdir       = './'
prefix       = 'silane'
wf_collect   = .TRUE.
/
&system
ibrav           = 1
celldm(1)       = 20
nat             = 5
ntyp            = 2
ecutwfc         = 25.0
nbnd            = 10
assume_isolated ='mp'
/
&electrons
diago_full_acc = .TRUE.
/
ATOMIC_SPECIES
Si 28.0855  Si_ONCV_PBE-1.1.upf
H  1.00794   H_ONCV_PBE-1.0.upf
ATOMIC_POSITIONS bohr
Si      10.000000   10.000000  10.000000
H       11.614581   11.614581  11.614581
H        8.385418    8.385418  11.614581
H        8.385418   11.614581   8.385418
H       11.614581    8.385418   8.385418
K_POINTS {gamma}

Run pw.in on 2 cores.

%%bash
mpirun -n 2 pw.x -i pw.in > pw.out

The output file pw.out contains information about the ground state calculation.

Step 2: Screening

The static dielectric screening is computed using the projective dielectric eigendecomposition (PDEP) technique. Check out the wstat.x input description and generate an input file for WEST called wstat.in.

Download this file in your current working directory:

%%bash
wget -N -q http://www.west-code.org/doc/training/silane/wstat.in

Let’s inspect the wstat.in file, input for wstat.x.

%%bash
cat wstat.in

{
"input_west": {
"qe_prefix": "silane",
"west_prefix": "silane",
"outdir": "./"
},
"wstat_control": {
"wstat_calculation": "S",
"n_pdep_eigen": 50
}
}

Run wstat.in on 2 cores.

%%bash
mpirun -n 2 wstat.x -i wstat.in > wstat.out

The output file wstat.out contains information about the PDEP iterations, and the dielectric eigenvalues can be found in the file west_prefix.wstat.save/wstat.json.

Step 3: GW

The GW electronic structure is computed treating the frequency integration of the correlation part of the self energy with the Contour Deformation techinique and by computing the dielectric screening at multipole frequencies with Lanczos iterations. Check out the wfreq.x input description and generate an input file for WEST called wfreq.in.

Download this file in your current working directory:

%%bash
wget -N -q http://www.west-code.org/doc/training/silane/wfreq.in

Let’s inspect the wfreq.in file, input for wfreq.x.

%%bash
cat wfreq.in

{
"input_west": {
"qe_prefix": "silane",
"west_prefix": "silane",
"outdir": "./"
},
"wstat_control": {
"wstat_calculation": "S",
"n_pdep_eigen": 50
},
"wfreq_control": {
"wfreq_calculation": "XWGQ",
"n_pdep_eigen_to_use": 50,
"qp_bandrange": [1,5],
"n_refreq": 300,
"ecut_refreq": 2.0
}
}

Run wfreq.in on 2 cores.

%%bash
mpirun -n 2 wfreq.x -i wfreq.in > wfreq.out

The output file wfreq.out contains information about the GW self-energy corrected electronic structure can be found in the file west_prefix.wstat.save/wfreq.json.