How to create Quantum Espresso databases for an electron-phonon calculation with Yambo (1st part)

Here I show step-by-step how to use Quantum Espresso to calculate phonons and electron-phonon matrix-elements on a regular q-grid, with the final aim to allow Yambo to read these databases and calculate the temperature dependent correction to the electronic states.

I suggest to use Quantum Espresso v-6.1.0. I usually create first scf and nscf folders.

1) In scf I run a standard scf calculation choosing the k grid and setting force_symmorphic=.true. An ${PREFIX}.save folder will be automatically created.
2) In the main directory I copy the previously created ${PREFIX}.save directory and I run a dVscf calculation, meaning a phonon calculation setting the flag electron_phonon = ‘dvscf’, and a q grid equivalent to the k grid you used before.

&inputph
tr2_ph = 1e-16
prefix = '6HSiC'
fildvscf = '6HSiC-dvscf'
fildyn = '6HSiC.dyn'
electron_phonon = 'dvscf',
epsil = .true.
trans = .true.
ldisp = .true.
verbosity = 'high'
nq1=10, nq2 =10, nq3=2
/


3) In nscf folder I run an nscf calculation, setting the number of bands nbnd = … force_symmorphic=.true. and the same q grid as before. A ${PREFIX}.save folder will be automatically created.
4) In the main directory I copy and then overwrite the previous ${PREFIX}.save directory with the new one. Now I run an elph calculation setting electron_phonon = ‘yambo’, and the q grid.

&inputph
fildvscf = '6HSiC-dvscf'
fildyn = '6HSiC.dyn'
verbosity = 'high'
epsil = .true.
ldisp = .true.
tr2_ph = 1e-16
prefix = '6HSiC'
electron_phonon = 'yambo',
trans = .false.
nq1=10, nq2 =10, nq3=2
/

5) In nscf/${PREFIX}.save folder I run p2y and yambo to get the standard Yambo databases. Then I move the newly generated SAVE folder in the elph_dir one, already present in the main directory.
6) In the elph_dir folder I will run then yambo_ph -i -V kpt. An input file is automatically generated and the MinusQ flag must be uncommented, or written (if not present) on top of q-points lisst “% QptCoord”. This input will be then executed by yambo_ph.
7) Finally run ypp_ph -g to create the ypp.in input file,

gkkp             # [R] Electron-Phonon databases
DBsPATH= "." # Path to the PW el-ph databases
PHfreqF= "none" # PWscf format file containing the phonon frequencies
PHmodeF= "none" # PWscf format file containing the phonon modes
GkkpExpand # Expand the gkkp in the whole BZ

which once executed, produces ndb.elph_gkkp databases.

See the next post to learn to use Yambo for calculating temperature dependent electronic energy levels in the Heine Allen Cardona approach.

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