Re: [Pw_forum] Band Offsets too large

[Dae Kwang Jun]

Dear Mostafa Youssef,

Thank you. I get values that are much closer to literature.

Dae Kwang Jun

On Thursday, 30 June 2016, Mostafa Youssef  wrote:

> Dear  Dae Kwang Jun
>
> Equation (1) that you wrote is the correct one.
>
> And you are right  bulk V_AlAs and bulk V_GaAs are obtained in a similar
> way as in the interface but you need bulk cells.  Their values can be
> anything , positive or negative it does not matter and  in fact they are
> arbitrary.
>
>
> Regards,
> Mostafa
>
>
___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

Re: [Pw_forum] Band Offsets too large

[Mostafa Youssef]

Dear  Dae Kwang Jun

Equation (1) that you wrote is the correct one.

And you are right  bulk V_AlAs and bulk V_GaAs are obtained in a similar way as 
in the interface but you need bulk cells.  Their values can be anything , 
positive or negative it does not matter and  in fact they are arbitrary.


Regards,
Mostafa

___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

Re: [Pw_forum] Band Offsets too large

[Dae Kwang Jun]

Dear Mostafa Youssef,

Thank you for your reply. I am not sure whether I understand what it is
meant by "where EVBM_AlAs is referred to bulk V_AlAs and EVBM_GaAs is
referred to bulk V_GaAs."
I am assuming that the complete formula is either

(1)
EVBM_offset = (EVBM_AlAs - bulk V_AlAs) - (EVMB_GaAs - bulk V_GaAs) +
del_V_interface_AlAs/GaAs

or

(2)
EVBM_offset = (EVBM_AlAs + bulk V_AlAs) - (EVMB_GaAs + bulk V_GaAs) +
del_V_interface_AlAs/GaAs

Also, I am assuming that bulk V_AlAs and bulk V_GaAs are obtained in the
same way as it is for the electrostatic potential for the interface and
that their values are positive. Could you elaborate?

Sincerely,

Dae Kwang Jun



On Thu, Jun 30, 2016 at 6:56 PM, Mostafa Youssef  wrote:

> Dear Dae Kwang Jun
>
>
> In addition for each bulk calculation one needs to calculate the bulk
> average electrostatic potential.  Then for each compound you refer its EVBM
> to the electrostatic potential calculated in  its bulk (not yet the
> interface).  Only then you can use the interface electrostatic potential
> according too:
>
> EVBM_offset =  EVBM_AlAs   -  EVBM_GaAs +  del_V_interface_AlAS/GaAS
>
> where EVBM_AlAs is referred to bulk V_AlAs and EVBM_GaAs is referred to
> bulk V_GaAs.
>
>
> Regards,
> Mostafa
>
> ___
> Pw_forum mailing list
> Pw_forum@pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

Re: [Pw_forum] Band Offsets too large

[Mostafa Youssef]

Dear Dae Kwang Jun


In addition for each bulk calculation one needs to calculate the bulk average 
electrostatic potential.  Then for each compound you refer its EVBM to the 
electrostatic potential calculated in  its bulk (not yet the interface).  Only 
then you can use the interface electrostatic potential according too:

EVBM_offset =  EVBM_AlAs   -  EVBM_GaAs +  del_V_interface_AlAS/GaAS

where EVBM_AlAs is referred to bulk V_AlAs and EVBM_GaAs is referred to bulk 
V_GaAs.


Regards,
Mostafa
___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

Re: [Pw_forum] Band Offsets too large

[Dae Kwang Jun]

Dear Mostafa Youssef,

I believe that I did that. I am not sure whether we both have the same
thing on mind, however. Here is what I did. I calculated the band
structures for both AlAs and GaAs using pw.x with calculation = 'bands'
after the scf calculations. The VB Maxima of AlAs and GaAs occur at the k
point gamma.  The bulk band structure calculations are done with 8
electrons for both GaAs and AlAs (I used the same pseudopotential that I
used for the interface calculation). Thus, I used the 4th energy at the
gamma k point in the AlAs.bands.dat file and the GaAs.bands.dat file. I
compared my band structures with literature, and I believe that they are
correct. From the interface calculation I find which compound has a higher
average electrostatic potential. I added the absolute value of
the difference in electrostatic potential from the interface
calculation  to the valence band energy of that compound (the one with
higher average electrostatic potential). I then substracted from this value
the energy of the valence maximum of the other compound. And I get the
(wrong) high value. Sorry for the long email. Please let me know your
thoughts.

Sincerely,

Dae Kwang Jun

On Thursday, 30 June 2016, Mostafa Youssef  wrote:

> Dear Dae Kwang Jun,
>
> You also need 2 bulk calculations for AlAs and GaAs to get their band
> edges with respect to to their bulk electrostatic potentials. Then you can
> use the interface potential to align the band edges of the two
> semiconductors.  It looks like you missed this step.
>
>
>
> Mostafa
> MIT
>
>
> 
>
___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

Re: [Pw_forum] Band Offsets too large

[Mostafa Youssef]

Dear Dae Kwang Jun,

You also need 2 bulk calculations for AlAs and GaAs to get their band edges 
with respect to to their bulk electrostatic potentials. Then you can use the 
interface potential to align the band edges of the two semiconductors.  It 
looks like you missed this step.



Mostafa
MIT


___
Pw_forum mailing list
Pw_forum@pwscf.org
http://pwscf.org/mailman/listinfo/pw_forum

[Pw_forum] Band Offsets too large

[Dae Kwang Jun]

Dear all,

I tried to calculate the band offset for GaAs-AlAs. However, the valence
band offsets that I am getting are too large. I used 6 unit cells of GaAs
and 6 unit cells of AlAs stacked in the 001 direction. For the offset I
used the potential line up method. I used pw.x pp.x average.x to find the
potential line up, and I used pw.x bands.x plotband.x to find the valence
band maxima. Most literature agrees that the VBO should be around 0.44 eV
to 0.50 eV. However, I am getting 2.49 eV, which is too large. What could
be causing this?

Sincerely,

Dae Kwang Jun

Here is one of the input files that I used for the GaAs-AlAs interface

&CONTROL
calculation = 'scf'
verbosity = 'high'
restart_mode = 'from_scratch'
tstress = .true.
tprnfor = .true.
outdir = '/home/files'
prefix = '001_5x5_GaAs-AlAs'
pseudo_dir = '/home/espresso-5.4.0/pseudo'
/
&SYSTEM
ibrav = 6
a = 5.65
c = 67.8
nat = 96
ntyp = 3
ecutwfc = 70.0
occupations = 'smearing'
degauss = 0.01
/
&ELECTRONS
mixing_beta = 0.4
diagonalization = 'david'
/
ATOMIC_SPECIES
Ga69.723Ga.pw-mt_fhi.UPF
Al26.981Al.pw-mt_fhi.UPF
As74.921As.pw-mt_fhi.UPF
ATOMIC_POSITIONS {angstrom}
Ga 0.00 0.00 0.00
Ga 0.00 2.825000 2.825000
Ga 2.825000 0.00 2.825000
Ga 2.825000 2.825000 0.00
As 1.412500 1.412500 1.412500
As 4.237500 4.237500 1.412500
As 4.237500 1.412500 4.237500
As 1.412500 4.237500 4.237500
Al 0.00 0.00 33.92
Al 0.00 2.825000 36.725002
Al 2.825000 0.00 36.725002
Al 2.825000 2.825000 33.92
As 1.412500 1.412500 35.312500
As 4.237500 4.237500 35.312500
As 4.237500 1.412500 38.137501
As 1.412500 4.237500 38.137501
Ga 0.00 0.00 5.65
Ga 0.00 2.825000 8.475000
Ga 2.825000 0.00 8.475000
Ga 2.825000 2.825000 5.65
As 1.412500 1.412500 7.062500
As 4.237500 4.237500 7.062500
As 4.237500 1.412500 9.887501
As 1.412500 4.237500 9.887501
Ga 0.00 0.00 11.30
Ga 0.00 2.825000 14.125000
Ga 2.825000 0.00 14.125000
Ga 2.825000 2.825000 11.30
As 1.412500 1.412500 12.712501
As 4.237500 4.237500 12.712501
As 4.237500 1.412500 15.537500
As 1.412500 4.237500 15.537500
Ga 0.00 0.00 16.950001
Ga 0.00 2.825000 19.775002
Ga 2.825000 0.00 19.775002
Ga 2.825000 2.825000 16.950001
As 1.412500 1.412500 18.362501
As 4.237500 4.237500 18.362501
As 4.237500 1.412500 21.187500
As 1.412500 4.237500 21.187500
Ga 0.00 0.00 22.60
Ga 0.00 2.825000 25.425001
Ga 2.825000 0.00 25.425001
Ga 2.825000 2.825000 22.60
As 1.412500 1.412500 24.012501
As 4.237500 4.237500 24.012501
As 4.237500 1.412500 26.837502
As 1.412500 4.237500 26.837502
Ga 0.00 0.00 28.25
Ga 0.00 2.825000 31.075001
Ga 2.825000 0.00 31.075001
Ga 2.825000 2.825000 28.25
As 1.412500 1.412500 29.662500
As 4.237500 4.237500 29.662500
As 4.237500 1.412500 32.487499
As 1.412500 4.237500 32.487499
Al 0.00 0.00 39.54
Al 0.00 2.825000 42.375000
Al 2.825000 0.00 42.375000
Al 2.825000 2.825000 39.54
As 1.412500 1.412500 40.962498
As 4.237500 4.237500 40.962498
As 4.237500 1.412500 43.787498
As 1.412500 4.237500 43.787498
Al 0.00 0.00 45.21
Al 0.00 2.825000 48.025002
Al 2.825000 0.00 48.025002
Al 2.825000 2.825000 45.21
As 1.412500 1.412500 46.612499
As 4.237500 4.237500 46.612499
As 4.237500 1.412500 49.437500
As 1.412500 4.237500 49.437500
Al 0.00 0.00 50.850002
Al 0.00 2.825000 53.675003
Al 2.825000 0.00 53.675003
Al 2.825000 2.825000 50.850002
As 1.412500 1.412500 52.262501
As 4.237500 4.237500 52.262501
As 4.237500 1.412500 55.087502
As 1.412500 4.237500 55.087502
Al 0.00 0.00 56.50
Al 0.00 2.825000 59.325001
Al 2.825000 0.00 59.325001
Al 2.825000 2.825000 56.50
As 1.412500 1.412500 57.912498
As 4.237500 4.237500 57.912498
As 4.237500 1.412500 60.737499
As 1.412500 4.237500 60.737499
Al 0.00 0.00 62.150002
Al 0.00 2.8250