2D material: h-BN sheet

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In this tutorial you will learn how to generate the Yambo SAVE folder for a 2D hBN sheet starting from a PWscf calculation.

Prerequisites

Previous modules

  • You must first follow the tutorial on bulk hBN.

You will need:

  • pw.x executable, version 5.0 or later
  • p2y executable
  • Follow the instructions in the File page and download and unpack the hBN-2D.tar.gz.

System characteristics

Atomic structure of 2D hBN

Hexagonal boron nitride sheet - 2D hBN:

  • 2D HCP lattice
  • Two atoms per cell, B and N (8 electrons)
  • Lattice constants: a = 4.716 [a.u.], c/a = 7 (supercell size)
  • Plane wave cutoff 40 Ry (~5000 RL vectors in wavefunctions)
  • SCF run: shifted 6x6x1 grid (12 k-points) with 4 bands
  • Non-SCF run: gamma-centred 6x6x1 (7 k-points) grid with 60 bands

DFT calculations

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

$ cd YAMBO_TUTORIALS/hBN-2D/PWSCF
$ ls
Inputs		Pseudos		PostProcessing		References
hBN_2D_scf.in	hBN_2D_nscf.in     hBN_2D_scf_bands.in  hBN_2D_nscf_bands.in 

The procedure is exactly the same as following in the Bulk_material:_h-BN tutorial, so no detailed explanations will be given here.

pw.x < hBN_2D_scf.in > hBN_2D_scf.out
pw.x < hBN_2D nscf.in > hBN_2D_nscf.out

The valence band maximum is computed at -4.29 eV. After these two runs, you should have a hBN_2D.save directory.

$ ls hBN_2D.save
data-file.xml charge-density.dat gvectors.dat B.pz-vbc.UPF N.pz-vbc.UPF
K00001	K00002 .... 	K00011	K00012

Conversion to Yambo format

Run the converter and check that the databases contain the information you expect:

$ cd hBN_2D.save
$ p2y
<---> DBs path set to .
<---> Index file set to data-file.xml
...
<--->  == P2Y completed ==

$ yambo -D
[RD./SAVE//ns.db1]------------------------------------------
Bands                           :  60
K-points                        :  7
G-vectors             [RL space]: 21817
Components       [wavefunctions]: 2736
...
[RD./SAVE//ns.wf]-------------------------------------------
Fragmentation                    :yes
Bands in each block             :  60
...
[RD./SAVE//ns.kb_pp_pwscf]----------------------------------
Fragmentation                    :yes
- S/N 0000908 -------------------------- v.04.01.02 r.00000 -

Note that the number of wavefunction components (G-vectors) is much higher than in the bulk hBN case (why?)

Continue using a SAVE 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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