Bulk material: h-BN

In this tutorial you will learn how to generate the Yambo SAVE folder for bulk hBN starting from a PWscf calculation.

Prerequisites

You will need:

• PWSCF input files and pseudopotentials for hBN bulk (Download here)
• pw.x executable, version 5.0 or later
• p2y executable

System characteristics

Atomic structure of bulk hBN

Hexagonal boron nitride - hBN:

• HCP lattice, ABAB stacking
• Four atoms per cell, B and N (16 electrons)
• Lattice constants: a = 4.716 [a.u.], c/a = 2.582
• Plane wave cutoff 40 Ry (1500 RL vectors in wavefunctions)
• SCF run: shifted 6x6x6 grid with 8 bands
• Non-SCF run: unshifted 6x6x2 grid with 100 bands

DFT calculations

Unpack the tarfile. It uses the same file structure as other yambo tutorials:

$ tar -xcvf hBN-bulk.tar
$ cd YAMBO_TUTORIALS/hBN/PWSCF
$ ls
Inputs		Pseudos		PostProcessing		References
hBN_scf.in	hBN_nscf.in     hBN_scf_plot_bands.in  hBN_nscf_plot_bands.in 

First run the SCF calculation to generate the ground-state charge density, occupations, Fermi level, and so on:

pw.x < hBN_scf.in > hBN_scf.out

The output reports 36 k-points. The valence band maximum is at 5.13eV.

Next run a non-SCF calculation to generate a set of Kohn-Sham eigenvalues and eigenvectors across a denser k-point mesh, for occupied and unoccupied states:

pw.x < hBN_nscf.in > hBN_nscf.out

Note the presence of the following flags in the input file:

wf_collect=.true.
force_symmorphic=.true.

which are needed for generating the Yambo databases. Full explanations of these variables are given on the quantum-ESPRESSO input variables page.

After these two runs, you should have a hBN.save directory:

$ ls hBN.save
data-file.xml

Conversion to Yambo format

PWscf output is converted to the Yambo format using the p2y (pwscf to yambo), found in the yambo bin directory. Enter the hbn.save directory and launch p2y:

$ cd hBN.save
$ p2y
[output]

The code reports some information about the system and generates a SAVE directory:

$ ls 
SAVE HB,in etc
$ ls SAVE
ns.db1 ns.wf ns.kb_pp_pwscf
ns.wf_fragments_1_1 ...
ns.kb_pp_pwscf_fragment_1 ...

Finally, let's move the SAVE directory into a new clean folder:

mv SAVE ../YAMBO/

Advanced users

p2y accepts several command line options:

$ p2y -H
dfadsfas