InAs band structure
InAs band structure
Hi all,
I am new to Abinit and have over the past few days been trying to simulate the band structure for bulk InAs. However it seems, that you have many choices for which Pseudopotentials to use. First I tried using the one that was used for bulk Si in the tutorial exercises, but that did not work, i.e. Abinit gave me an error (I am not sure why, since I find it hard to interpret the files specifying the Pseudopotentials).
My question is therefore: Which kind of Pseudopotential should I use for bulk InAs?
Also my end goal is actually not to calculate bulk band structure but rather band structure for finite InAs nanowires. I am however not sure how to do calculations on finite lattices. How is that done? I suppose you like, the H2 molecule, simply build up a system of finite building blocks, rather than assume an infinite lattice as in the case of the Si exercises.
I am new to Abinit and have over the past few days been trying to simulate the band structure for bulk InAs. However it seems, that you have many choices for which Pseudopotentials to use. First I tried using the one that was used for bulk Si in the tutorial exercises, but that did not work, i.e. Abinit gave me an error (I am not sure why, since I find it hard to interpret the files specifying the Pseudopotentials).
My question is therefore: Which kind of Pseudopotential should I use for bulk InAs?
Also my end goal is actually not to calculate bulk band structure but rather band structure for finite InAs nanowires. I am however not sure how to do calculations on finite lattices. How is that done? I suppose you like, the H2 molecule, simply build up a system of finite building blocks, rather than assume an infinite lattice as in the case of the Si exercises.
Re: InAs band structure
aaaa202 wrote:I tried using the one that was used for bulk Si in the tutorial exercises
You meant the same type, not literaly the same PP, right? In any case, for In and As you can find pseudopotentials at the Abinit website > Atomic Data/Pseudopotentials > Normconserving pseudopotentials.
aaaa202 wrote:I am however not sure how to do calculations on finite lattices. How is that done?
This question is too broad. I suspect the overall logic is similar to surface calculations (see lesson 4) but I've never done nanowire calculations myself.
Raul Laasner
Netherlands Institute for Space Research
Netherlands Institute for Space Research
Re: InAs band structure
Recent pseudo potential have been developed in Norm Conserving here : http://www.matsimresearch.com/
Or PAW atomic data here : http://www.abinit.org/downloads/PAW2
In any case, you should test the pseudos you use and validate the results against literature before going to nanowire.
For nanowire, you can do as for the H2 molecule : a big empty box with a nano wire inside.
Note that for such a system the energy cutoff might considerably increase and thus PAW may be the best choice for you.
Or PAW atomic data here : http://www.abinit.org/downloads/PAW2
In any case, you should test the pseudos you use and validate the results against literature before going to nanowire.
For nanowire, you can do as for the H2 molecule : a big empty box with a nano wire inside.
Note that for such a system the energy cutoff might considerably increase and thus PAW may be the best choice for you.
Re: InAs band structure
thanks for the answers, though I might need a little more help.
Say I download pseudopotentials for In and As from http://www.abinit.org/downloads/pseudodojo/pseudodojo. How do I tell my in file to use these for the calculation of the band structure? I remember in the tutorial for Si there was a line in the tbase3_x file, which specified ../../../Psps_for_tests/14si.pspnc, i.e. to use the file 14si.pspnc as pseudopotential. Should I replace this one line with the location of the Pseudopotential of In and As?
Also it seems that the pseudopotential files I can download from: http://www.pseudodojo.org/dojoauto.html?atom=In (or the PAW atomic datasets  do these contain information about the pseudopotential?) are not of the same type as 14si.pspnc. Will abinit understand these?
Say I download pseudopotentials for In and As from http://www.abinit.org/downloads/pseudodojo/pseudodojo. How do I tell my in file to use these for the calculation of the band structure? I remember in the tutorial for Si there was a line in the tbase3_x file, which specified ../../../Psps_for_tests/14si.pspnc, i.e. to use the file 14si.pspnc as pseudopotential. Should I replace this one line with the location of the Pseudopotential of In and As?
Also it seems that the pseudopotential files I can download from: http://www.pseudodojo.org/dojoauto.html?atom=In (or the PAW atomic datasets  do these contain information about the pseudopotential?) are not of the same type as 14si.pspnc. Will abinit understand these?
Re: InAs band structure
The structure of the 'files' file is described here: http://www.abinit.org/doc/helpfiles/for ... tml#intro1. Yes, you should replace 14si.pspnc with your own ones (either relative or full path). Each PP should be on a separate line. The PAW formalism is conceptually different, but from the user's point of view, analogous, to the pseudopotential approximation. In simple terms, it is usually better than PPs. You might start with normconserving PPs if you are new to DFT, and then proceed to the tutorials on PAW.
Raul Laasner
Netherlands Institute for Space Research
Netherlands Institute for Space Research
Re: InAs band structure
It doesn't seem like abinit will recognize the Pseudopotential file generated by http://www.pseudodojo.org/dojoauto.html?atom=In. The format is .pspn8, which I can save as a text document. Am I doing it wrong?
I choose Indium in the list of element and select Ind.out and click download 'psp8' file.
I choose Indium in the list of element and select Ind.out and click download 'psp8' file.
Re: InAs band structure
What is the error message? Perhaps you should be using a newer version of Abinit? Just a guess.
Raul Laasner
Netherlands Institute for Space Research
Netherlands Institute for Space Research
Re: InAs band structure
hmm i Think abinit does not recognize the file format for the generated pseudopotential file. If I generate it using your link the format is .psp8 ... is that a valid format? maybe Im failing to save it the right way.
Re: InAs band structure
Works for me. Make sure you use at least version 7.10.5. If there are still issues, find older pseudopotentials here http://www.abinit.org/downloads/psplinks/pseudopotentials.
Raul Laasner
Netherlands Institute for Space Research
Netherlands Institute for Space Research
Re: InAs band structure
hmm I think my problem is that when I save the pseudopotential file it messes up the format. It saves it as a .txt document and when I open it I can see that the text format is completely messed up. How do you save it to your computer? Is it because I am using windows, and I should use linux instead to get the right format of the Pseudopotential files?
Re: InAs band structure
I save the PP with the psp8 extension. I suggest you try it on Linux. I'm not familiar with Windows and am thus unable to help in that regard.
Raul Laasner
Netherlands Institute for Space Research
Netherlands Institute for Space Research
Re: InAs band structure
I have now managed to generate the band structure for InAs, which was the end goal. However it seems that the wavefunctions do not converge and I end up with the plot below with alot of fringes in the band structure.
I have made a convergence study with respect to the lattice parameter so I am not sure, what causes the problem not to converge? Which parameters can I change that will affect convergence?
I have made a convergence study with respect to the lattice parameter so I am not sure, what causes the problem not to converge? Which parameters can I change that will affect convergence?
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 InAswurtzite.png (60.13 KiB) Viewed 14155 times

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Re: InAs band structure
Hi!
1] What do you mean by converged the lattice parameters?
2] It looks like typical bands obtained with unconverged ecut and/or ngkpt. Did you converge the energy bands wrt these two parameters?
Best regards,
Igor
1] What do you mean by converged the lattice parameters?
2] It looks like typical bands obtained with unconverged ecut and/or ngkpt. Did you converge the energy bands wrt these two parameters?
Best regards,
Igor
Re: InAs band structure
I have now achieved the following plot of the band structure. Unfortunately it does not look at all like in this article (http://arxiv.org/pdf/condmat/0609616.pdf), where they calculate InAs wurtzite band structure in the GW approach. Do you have any idea how that might be? Have I done something wrong in my program?
Code: Select all
#Bulk InAs wurtzite
#
# Computation of the band structure.
# First, a SCF density computation, then a nonSCF band structure calculation.
ndtset 2
#Dataset 1 : usual selfconsistent calculation
kptopt1 1 # Option for the automatic generation of k points,
# taking into account the symmetry
nshiftk1 1
shiftk1 0.0 0.0 0.0 # These shifts will be the same for all grids
# 0.5 0.0 0.0
# 0.0 0.5 0.0
# 0.0 0.0 0.5
ngkpt1 12 12 12
prtden1 1 # Print the density, for use by dataset 2
toldfe1 1.0d10 # This value is way too large for most realistic studies of materials
#Dataset 2 : the band structure
iscf2 2
getden2 1
kptopt2 3
nband2 8
ndivk2 30 36 51 # 10, 12 and 17 divisions of the 3 segments, delimited
# by 4 points.
kptbounds2 0.0 0.0 0.5 # A point
0.0 0.0 0.0 # Gamma point
2/3 1/3 0 # K point
1.0 1.0 1.0 # Gamma point in another cell.
tolwfr2 1.0d13
enunit2 1 # Will output the eigenenergies in eV
#Definition of the unit cell for InAs wurtzite
acell 7.8602817707 7.8602817707 12.835877418
angdeg 90. 90. 120.
#rprim 0.5 0.86602540378 0.0
# 0.5 0.86602540378 0.0
# 0.0 0.0 1.0
spgroup 186
#Definition of the atom types
ntypat 2 # There is only one type of atom
znucl 49 33
#Definition of the atoms
natom 4 # There are four atoms in the unit cell
natrd 2
typat 1 2
xred # This keyword indicate that the location of the atoms
# will follow, one triplet of number for each atom
2/3 1/3 3/8
#1/3 2/3 7/8
2/3 1/3 0.0
#1/3 2/3 1/2
#Definition of the planewave basis set
ecut 50 # Maximal kinetic energy cutoff, in Hartree
prtvol 2
#Definition of the SCF procedure
nline 30
nnsclo 30
nstep 50 # Maximal number of SCF cycles
diemac 12.0 # Although this is not mandatory, it is worth to
# precondition the SCF cycle. The model dielectric
# function used as the standard preconditioner
# is described in the "dielng" input variable section.
 Attachments

 InAswurtzite2.png (34.98 KiB) Viewed 14122 times
Re: InAs band structure
I have not look at the reference but just to give you some hints, the band structure depends on the functional you use LDA/GGA and event the variant of functional (which LDA or GGA).
Then GW can be used for semiconductor to correct the band gap and more generally the eigen energies and thus the band structure.
Finally, the band structure also depends on the pseudo potential you use in case of norm conserving or atomic data in the cas of PAW calculation.
Jordan
Then GW can be used for semiconductor to correct the band gap and more generally the eigen energies and thus the band structure.
Finally, the band structure also depends on the pseudo potential you use in case of norm conserving or atomic data in the cas of PAW calculation.
Jordan
Re: InAs band structure
okay thanks, Im now trying to perform calculations using the gw method instead.
Actually can you help me understand something: As far as I know from litterature on DFT, it is a theory for calculating the ground state properties of the system. The Kohn sham energies and orbitals have no physical meaning themselves. So how is it that we are able to obtain the band structure in the first place?
Also can you explain to me how the nshiftk and shiftk work, I am not sure how the kgrid is assembled from them. I am now trying to simulate for wurtzite but I get the error that my kgrid does not respect the symmetries of the problem. How do I know what to choose?
Edit: How exactly are my values for ecutsigx, npwsigx, or nshsigx related to my kpoint grid? Because when I change to a grid that preserves the symmetry I get the error:
One of the three variables ecutsigx, npwsigx, or nshsigx
must be nonnull. Returning.
src_file: m_gsphere.F90
src_line: 1906
Actually can you help me understand something: As far as I know from litterature on DFT, it is a theory for calculating the ground state properties of the system. The Kohn sham energies and orbitals have no physical meaning themselves. So how is it that we are able to obtain the band structure in the first place?
Also can you explain to me how the nshiftk and shiftk work, I am not sure how the kgrid is assembled from them. I am now trying to simulate for wurtzite but I get the error that my kgrid does not respect the symmetries of the problem. How do I know what to choose?
Code: Select all
# Crystalline silicon
# Calculation of the GW correction to the direct band gap in Gamma
# Dataset 1: ground state calculation
# Dataset 2: calculation of the kss file
# Dataset 3: calculation of the screening (epsilon^1 matrix for W)
# Dataset 4: calculation of the SelfEnergy matrix elements (GW corrections)
ndtset 4
ngkpt 2 2 2 # Density of k points used for the automatic tests of the tutorial
#ngkpt 4 4 4 # Density of k points needed for a converged calculation
nshiftk 4
shiftk 0.0 0.0 0.0 # This grid contains the Gamma point, which is the point at which
0.0 0.5 0.5 # we will compute the (direct) band gap. There are 19 k points
0.5 0.0 0.5 # in the irreducible Brillouin zone, if ngkpt 4 4 4 is used.
0.5 0.5 0.0
istwfk *1 # For the GW computations, do not take advantage of the
# specificities of k points to reduce the number of components of the
# wavefunction.
# Dataset1: usual selfconsistent groundstate calculation
# Definition of the kpoint grid
shiftk1 0.5 0.5 0.5 # This grid is the most economical, but does not contain the Gamma point.
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
istwfk1 *0 # For the ground state, let the code use the timereversal symmetry
prtden1 1 # Print out density
# Dataset2: calculation of kss file
# Definition of kpoints
iscf2 2 # Non selfconsistent calculation
getden2 1 # Read previous density file
kssform2 3
nband2 105
nbandkss2 100 # Number of bands to store in KSS file
nbdbuf2 5
# Dataset3: Calculation of the screening (epsilon^1 matrix)
optdriver3 3 # Screening calculation
getkss3 1 # Obtain KSS file from previous dataset
nband3 25 # Bands to be used in the screening calculation
ecutwfn3 3.6 # Planewaves to be used to represent the wavefunctions
ecuteps3 6.0 # Dimension of the screening matrix
ppmfrq3 16.7 eV # Imaginary frequency where to calculate the screening
# Dataset4: Calculation of the SelfEnergy matrix elements (GW corrections)
optdriver4 4 # SelfEnergy calculation
getkss4 2 # Obtain KSS file from dataset 1
getscr4 1 # Obtain SCR file from previous dataset
nband4 100 # Bands to be used in the SelfEnergy calculation
ecutwfn4 5.0 # Planewaves to be used to represent the wavefunctions
ecutsigx4 6.0 # Dimension of the G sum in Sigma_x
# (the dimension in Sigma_c is controlled by npweps)
nkptgw4 1 # number of kpoint where to calculate the GW correction
kptgw4 # kpoints
0.000 0.000 0.000 # (Gamma)
bdgw4 4 5 # calculate GW corrections for bands from 4 to 5
icutcoul4 3 # old deprecated value of icutcoul, only used for legacy
#Definition of the unit cell for InAs wurtzite
acell 7.8602817707 7.8602817707 12.835877418
angdeg 90. 90. 120.
#rprim 0.5 0.86602540378 0.0
# 0.5 0.86602540378 0.0
# 0.0 0.0 1.0
spgroup 186
# Definition of the atom types
ntypat 2 # There are two types of atoms
znucl 49 33 # The keyword "znucl" refers to the atomic number of the
# possible type(s) of atom. The pseudopotential(s)
# mentioned in the "files" file must correspond
# to the type(s) of atom. Here they are In and As.
# Definition of the atoms
natom 4 # There are four atoms
natrd 2
typat 1 2 # They both are of type 1, that is, Silicon.
xred # This keyword indicate that the location of the atoms
# will follow, one triplet of number for each atom
2/3 1/3 3/8
#1/3 2/3 7/8
2/3 1/3 0.0
#1/3 2/3 1/2
# Definition of the planewave basis set (at convergence 16 Rydberg 8 Hartree)
ecut 8.0 # Maximal kinetic energy cutoff, in Hartree
# Definition of the SCF procedure
nstep 10 # Maximal number of SCF cycles
diemac 12.0 # Although this is not mandatory, it is worth to
# precondition the SCF cycle. The model dielectric
# function used as the standard preconditioner
# is described in the "dielng" input variable section.
# Here, we follow the prescription for bulk silicon.
tolwfr 1.0d10
# This line added when defaults were changed (v5.3) to keep the previous, old behaviour
iscf 5
#%%<BEGIN TEST_INFO>
#%% [setup]
#%% executable = abinit
#%% [files]
#%% files_to_test =
#%% tgw1_9.out, tolnlines= 70, tolabs= 7.000e02, tolrel= 3.000e02, fld_options= ridiculous
#%% psp_files = 14si.pspnc
#%% [paral_info]
#%% max_nprocs = 4
#%% [extra_info]
#%% authors =
#%% keywords = GW
#%% description =
#%%<END TEST_INFO>
Edit: How exactly are my values for ecutsigx, npwsigx, or nshsigx related to my kpoint grid? Because when I change to a grid that preserves the symmetry I get the error:
One of the three variables ecutsigx, npwsigx, or nshsigx
must be nonnull. Returning.
src_file: m_gsphere.F90
src_line: 1906
Re: InAs band structure
I won't be able to help you with all your question but i'll give a try
1) Yes you are right, DFT is not able, in theory to produce the band structure of the system. Indeed, we just know that the density and only the density matches between the real system and the fake KS system. But, surprisingly, it appears that the band structure produced with the KS wavefunctions is usually very close to the real system one and thus we make the short cut and assumption saying the band structure calculated with DFT+KS is the one of the system. But, a priori, nothing allows us to do this.
2) the shiftk and nshiftk are simply a way of better sampling the BZ with a reduced number of kpt compared to non shift grid. Read e.g. H. J. Monkhorst and J. D. Pack, Phys. Rev. B 13, 5188 (1976).
Usually if there is a message telling you the kmesh does not respect the symmetries of the problem, it means the Gamma point might have been shift and so removing the shifts should help.
Cheers
1) Yes you are right, DFT is not able, in theory to produce the band structure of the system. Indeed, we just know that the density and only the density matches between the real system and the fake KS system. But, surprisingly, it appears that the band structure produced with the KS wavefunctions is usually very close to the real system one and thus we make the short cut and assumption saying the band structure calculated with DFT+KS is the one of the system. But, a priori, nothing allows us to do this.
2) the shiftk and nshiftk are simply a way of better sampling the BZ with a reduced number of kpt compared to non shift grid. Read e.g. H. J. Monkhorst and J. D. Pack, Phys. Rev. B 13, 5188 (1976).
Usually if there is a message telling you the kmesh does not respect the symmetries of the problem, it means the Gamma point might have been shift and so removing the shifts should help.
Cheers
Re: InAs band structure
Hello aaaa2.
I have followed your whole discussion.
I am also a nurse in this work of Abinit.
I just want to know how you run the code,
with which .files file and with what command?
I have followed your whole discussion.
I am also a nurse in this work of Abinit.
I just want to know how you run the code,
with which .files file and with what command?