ypp Exciton Plot

[mdvorak]

Hello,
I have a couple of questions regarding exciton plotting with ypp. I am trying to plot the exciton with hole fixed for crystalline silicon. I would like a 3D plot over a few unit cells to look at the exciton spread out through the crystal, like in the H2 chain tutorial. It seems like I can only get a single unit cell though. The ypp input:

wavefunction # [R] Wavefunction
excitons # [R] Excitons
Format= "c" # Output format [(c)ube/(g)nuplot/(x)crysden]
Direction= "123" # [rlu] [1/2/3] for 1d or [12/13/23] for 2d [123] for 3D
FFTGvecs= 1471 RL # [FFT] Plane-waves
States= "25 - 25" # Index of the BS state(s)
Degen_Step= 0.0100 eV # Maximum energy separation of two degenerate states
% Cellsx
4 | 4 | 4 | # Number of cell repetitions (even or 1)
%
% Hole
0.000 | 0.000 | 0.000 | # [cc] Hole position in unit cell
%

And the header of the .cube file:

CUBE FILE
Generated with YPP 3 2
3 0 0 0
18 0 0.28334 0.28334
18 0.28334 0 0.28334
18 0.28334 0.28334 0
-1 -1 0 0 0
14 14 0 0 0
14 14 2.55003 2.55003 2.55003

No matter what I change cell repetitions to (like | 4 | 4| 4 |), I only get 18 divisions along each vector with step size 0.28334. 18*SQRT(0.283^2+0.283^2) gives the magnitude of my rprim vectors, 7.204, so the data is still confined to one unit cell. I would like to see the exciton over a few cells like the H2 chain.
The volumetric data after the header of the .cube file - I assume this is the norm squared of the wave function? Or just norm?
The energy differences between electron and hole listed in the exciton o.exc_amplitude_at_## are the QP corrected values, NOT the bare KS eigenvalues, right?

Thank you,
Marc Dvorak

[Daniele Varsano]

Dear Marc,

No matter what I change cell repetitions to (like | 4 | 4| 4 |)

That's quite strange, but I think that happens because as I can say from your cut and paste you have the variable
% Cellsx instead of Cells, may be you added an x by mistake. Anyway, your post give me the opportunity to note that
there is an error in the input file description that we should correct soon: the number of cell repetition have to be ODD!!,
in order mantain the hole in the center. Anyway the code should do it automatically, to the nearest odd number.
Moreover I think that the cube format has been not checked for non-cubic unit cells, try it, if not working I suggest you to move
to xcrysden format.

The volumetric data after the header of the .cube file - I assume this is the norm squared of the wave function? Or just norm?

Should be norm squared!!

The energy differences between electron and hole listed in the exciton o.exc_amplitude_at_## are the QP corrected values, NOT the bare KS eigenvalues, right?

Yes, if you applied the correction, otherwise they are the bare KS.

Cheers,

Daniele

[mdvorak]

Daniele,
Thank you, my exciton plotting is now working great (for .cube or .xsf). I suspect it was the mistyped "x". I am apparently not applying the QP corrections correctly. When I try to implement them, they are not being read and just the KS eigenvalues are being used. This is out of place on the forum, but can you specify the syntax for reading the ndb.QP file? I have

KfnQPdb= "E < /panfs/storage/scratch/mdvorak/exciton/zno/yambo21/SAVE/ndb.QP"

with all the other QP variables as their default - no scissor shift, nothing on W or Z. Is the "E < " necessary? Where in the report file would I see the QP corrections loaded? I only see reference to QP corrections here:

[04] External QP corrections (X)
================================


[05] External QP corrections (X)
================================

and these are blank! The printed energies at each k-point are the LDA values, not the QP values from the database.

Thank you,
Marc Dvorak

[Daniele Varsano]

Dear Marc,

the correct syntax should be:

Code: Select all

KfnQPdb="E < SAVE/ndb.QP"

,
so your input file should work.
Now I'm not sure that the thy are reported in the amplitude file, but
you can easily check if they are read correctly looking at the independent-particle
BSE spectra. It is reported in the BSE output spectrum file in the 4ty and 5th column.
There, looking at the onset you should recognize if they are correctly read.
Anyway, I'm quite sure they are not read, as in the report you should find
something like:

Code: Select all

[06] External QP corrections (K)

.
Try also to have a look to other post in the forum, as other people encountered
the same problem, somehow related with the netcdf libs.

Cheers,
Daniele

[claudio]

Dear Marc

I do not remember in which version the Quasi-Particle correction for the excitons amplitude
have been introduced but they are for sure supported in the last version of Yambo 3.2.4

Claudio

[myrta gruning]

Dear Marc

beside the report give a look at the log, it may tell you whether the database is read and if not why

if it is read you will find something similar to

Code: Select all

 
<01h-21m-28s> [09] External QP corrections (K)
<01h-21m-28s> [QP@K] E<SAVE/ndb.QP[ PPA XG:4989 Xb:1   500 Scb:1   500]

Best,
m

[mdvorak]

Thank you! Everything is working great now. The QP corrections are being read, I see it in the log. The peak in the absorption has also shifted by the QP correction to its proper spot around 3.5 eV.

Marc

[andrea marini]

Dear Mark, for our informations. What was the problem ?

Andrea

[mdvorak]

User error. I was looking for the database to be read here:

[01] Files & I/O Directories
============================

CORE databases in .
Additional I/O in .
Communications in .
Input file is yambo.in
Report file is ./r_optics_bse_em1s_em1d_ppa_bss
Log file is ./l_optics_bse_em1s_em1d_ppa_bss

under additional I/O. It does not appear here but is read later in its own section as you all have pointed out. My version (3.2.3.11) reports the KS energy difference in the amplitude list as well. The combination of these two led me to believe that QP energies were not being read.

Marc