[QE-users] Error with pw2gw.x

[Shivesh Sivakumar]

Hello all,

I am trying to calculate the momentum matrix elements for my material with
HSE and HSE+U etc, which is not supported in QE. I already calculated the
matrix elements with PBE, but I want to see if the optical selection rules
change when the hybrid functional is turned on.

I set out to do this with the help of BerkeleyGW- They outline a relatively
simple way that takes into account only the wavefunctions in the inner
product (i.e. the dipole matrix element). This 'finite difference' method
is mentioned in the BerkeleyGW manual ( https://arxiv.org/pdf/1111.4429.pdf,
equation 46).

I tried porting my wavefunctions from QE to GW using pw2gw.x but I am
encountering some errors. Please bear with me while I outline the procedure
I used, and the doubts I have.

1) Use pp.x to save the wavefunction in a readable format. Here is my pp.x
input. To start with, I just want to calculate the matrix element between
the band edges at gamma point. The input below generates the wavefunction
at VBM GAMMA.

&INPUTPP
prefix='CrPs4SCF'
outdir='./'
filplot='wfn'
plot_num=0
kpoint=1
kband=92
/


&PLOT
output_format=5
iflag=3
filepp='./plots'
fileout='./exportgcf'
/

This seems to generate the wavefunction just fine. Did not encounter an
issue here.

2) To convert this wavefunction to a format that BGW can read, I used
pw2gw.x. Here's the input:

&input_pw2bgw
   prefix = 'CrPs4SCF'
   outdir = './'
   real_or_complex = 2
   wfng_flag = .true.
   wfng_file = 'realwfnGW'
   wfng_kgrid = .false.
   wfng_nk1 = 4
   wfng_nk2 = 6
   wfng_nk3 = 1
/

This seems to lead to an error :   Error in routine pw2gw (1):     reading
inputpp namelist.

Would someone be able to tell me where I might have gone wrong? I am also
confused as to what input the pw2gw file reads - Is it the wavefunction
directly from my first step i.e. the output 'plots' from my pp.x
calculation? or should I copy paste the whole SCF directory that includes
the .xml file and charge density data?

Best,
Shivesh Sivakumar
University of Washington-Seattle
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