Bulk material: h-BN

In this module 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
• pw.x executable, version 5.0 or later
• p2y and yambo executables
• Follow the instructions in the File page and download and unpack the hBN.tar.gz.

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 6x6x2 grid (12 k-points) with 8 bands
• Non-SCF run: gamma-centred 6x6x2 (14 k-points) grid with 100 bands

Conversion to Yambo format

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

$ cd hBN.save
$ p2y
...
<---> DBs path set to .
<---> Index file set to data-file.xml
<---> Header/K-points/Energies... done
...
<---> == DB1 (Gvecs and more) ...
<---> ... Database done
<---> == DB2 (wavefunctions)  ... done ==
<---> == DB3 (PseudoPotential) ... done ==
<--->  == P2Y completed ==

This output repeats some information about the system and generates a SAVE directory:

$ ls SAVE
ns.db1  ns.wf  ns.kb_pp_pwscf
ns.wf_fragments_1_1 ...
ns.kb_pp_pwscf_fragment_1 ...

These files, with an n prefix, indicate that they are in netCDF format, and thus not human readable. However, they are perfectly transferable across different architectures. You can check that the databases contain the information you expect by launching Yambo using the -D option:

$ yambo -D
[RD./SAVE//ns.db1]------------------------------------------
Bands                           : 100
K-points                        : 14
G-vectors             [RL space]:  8029
Components       [wavefunctions]: 1016
...
[RD./SAVE//ns.wf]-------------------------------------------
Fragmentation                    :yes
...
[RD./SAVE//ns.kb_pp_pwscf]----------------------------------
Fragmentation                    :yes
- S/N 006626 -------------------------- v.04.01.02 r.00000 -

In practice we suggest to move the SAVE folder into a new clean folder.

In this tutorial however, we ask instead that you continue using a SAVE folder that we prepared previously:

$ cd ../../YAMBO
$ ls
SAVE

Summary

From this tutorial you've learned:

• How to run a DFT calculation with PWscf in preparation for Yambo
• Convert the DFT output into the Yambo format
• How to check the contents of the netCDF databases

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