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

Material properties

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)

Files

Unpack the TARFILE:

$ tar -xcvf hBN-bulk.tar
$ cd hBN/PWSCF
$ ls
hbn_bands.in	hbn_nscf.in hbn_scf.in	hbn_scf_b.in REFERENCES

DFT calculations

First run the SCF calculation in the usual manner, e.g.

pw.x < hBN_scf.in > hBN_scf.out

and then the non-SCF calculation to generate a set of Kohn-Sham eigenvalues and eigenvectors across a denser k-point mesh and 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 the next step. 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