[QE-users] Fwd: how to extract the matrix elements from the valence bands to conduction bandsat the Brillouin zone center?

[Yu, Jingjing]

Could anyone tell me how to write the right codes and execute the right 
commands to get the matrix elelments from the valence bands to the 
conduction bands at the Brilloun Zone in Quantum espresso?
Thank you very much!

Best regards,
Jingjing
-------- Forwarded Message --------
Subject: 	[Extern] [QE-users] how to extract the matrix elements from 
the valence bands to conduction bandsat the Brillouin zone center?
Date: 	Thu, 9 Nov 2023 23:43:53 +0100
From: 	Yu, Jingjing <jy95vowa at studserv.uni-leipzig.de>
Reply-To: 	Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
To: 	users at lists.quantum-espresso.org



Hello everyone,

I am wondering how to extract the matrix elements from the valence bands 
to the conduction bands at the Brillouin zone center, Gamma point in 
Quantum espresso.

I tried to calculate the matrix elements of Si and I got the result in 
the p_avg.dat. But it looks weird, because the the corresponding matrix 
elements along x, y ,z directions (for example, three values |/M/_11 |^2 
along x.y,z directions) are totally different shown below.

*&p_mat nbnd=   6, nks=  29 /
             0.000000  0.000000  0.000000      4
   1
      0.00022045     0.02823071     0.03700090     0.13449672
      0.00458980     0.00203767     0.00400515     0.00964742
   2
      0.00327610     0.02056865     0.04947954     0.00093171
      0.00019941     0.07363126     0.09566180     0.03136617
   3
      0.00146403     0.07631971     0.06399219     0.00701410
      0.00016914     0.00944635     0.02901511     0.16348040*

Because Si has face-centered cubic crystal structure and the matrix 
elements  located at the same positions along x, y, z directions should 
be same, right?

My general calculation procedures are shown below:

*1. run scf.in*

&control
     calculation = 'scf'
     restart_mode='from_scratch'
     prefix = 'si'
     outdir = './outdir'
     pseudo_dir = '/home/yyb/qe-7.0/pseudo'
/
&system
     ibrav=2, celldm(1) =10.410909236,
     nat=2, ntyp=1,
     ecutwfc=40
     ecutrho=320
     nbnd=6
     occupations='smearing', smearing='gaussian',degauss=0.005
     !nosym = .true.
     !noinv = .true.
     !occupations = 'fixed'
     !input_dft = 'gaupbe'
     !nqx1 = 4, nqx2 = 4, nqx3 = 4,
     !x_gamma_extrapolation = .false.
     ! exxdiv_treatment = 'none'
/
&electrons
     conv_thr=1e-10
/
ATOMIC_SPECIES
  Si  28.0855  Si_ONCV_PBE-1.0.upf

ATOMIC_POSITIONS (alat)
  Si 0.00 0.00 0.00
  Si 0.25 0.25 0.25
K_POINTS (automatic)
   8 8 8 0 0 0

*2.run bands.x*

&bands
   outdir='./outdir/'
   prefix='si'
   filband='si.bands.dat'
   lp=.true.
   filp = 'p_avg.dat'
/

I don't know how to get the right result and could anyone who has the 
experience give me some help or suggestions?
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