[Wannier] quantum conductance and band structures
Zeina Salman
zaldolam at email.uark.edu
Thu Mar 31 23:00:34 CEST 2016
Dear users and developers,
I have been using wannier90. v1.2 for a while. I have run many examples in
the tutorial and other papers to make sure that I have good understanding.
I have focused recently on CNT, graphene, and other carbon based materials
as they are related to my research. However, I realize that I still face
some issues sometimes that might be related to misunderstanding some
concepts.
My first question is that why do I see straight bands (lines) when plotting
the band structure of a system? Are these valance bands besides having the
conduction bands? Is there a problem with the projections that I am
choosing or the system itself? What can be the reason for having these
bands as straight lines?
My second question is why does the quantum conductance plot has kind of
spikes at specific energy values, while it has zero values at others? I
understand it depends on the system, its electronic properties, etc. I
tried to run the calculations for systems in published papers as a way to
confirm mine. However, I do not get continuous values for the quantum
conductance as the published ones when I run the calculations for the same
system as theirs. Is it because of different methods of calculations? I am
totally confused although I realize it is quantum conductance not classical
conductance. Here is the link to one paper: Kindly, have a look at figure
(4). http://www.ncbi.nlm.nih.gov/pubmed/21406839
Last question is there any formula that I can use to calculate the current
from the quantum conductance? If so, what is it? I know that conductance
and current are related, but I am not sure about the quantum conductance vs
energy obtained using wannier90 codes.
Would you please help me with it? Any feedback and comments are greatly
appreciated. My questions may seem to you viral and basics, but I need
your help with them as I am working on something that I do not have the
required background in it. Feel free to advice and suggest anything because
I am willing to understand what I am doing. Apologies for the long email
and many thanks in advance
I appreciate your time
Zeina
Below are my scf and win input files for a system on 16 carbon atoms
forming a linear chain. Also, the attached file is an image that shows the
quantum conductance.
*scf.in <http://scf.in> *
&CONTROL
calculation = 'scf',
restart_mode= 'from_scratch',
verbosity = 'high'
pseudo_dir = '/share/apps/espresso/espresso-5.1/wannier90-1.2/pseudo',
outdir = './',
prefix = '16cc',
tstress = .f.,
tprnfor = .t.,
/
&SYSTEM
ibrav = 0,
cosbc = 0.,
cosac = 0.,
cosab = 0.,
nat = 16,
ntyp = 1,
ecutwfc = 30.,
ecutrho = 240.,
occupations = 'smearing',
smearing = 'gauss',
degauss = 0.03,
nspin = 1,
/
&ELECTRONS
mixing_beta = 0.4
electron_maxstep = 1000,
conv_thr = 1.D-10,
/
CELL_PARAMETERS {angstrom}
20.458886621 0.000000000 0.000000000
0.000000000 25.000000000 0.000000000
0.000000000 0.000000000 25.000000000
ATOMIC_SPECIES
C 12.0107 C.pbe-rrkjus.UPF
ATOMIC_POSITIONS (angstrom)
C -14.491185639 2.648257939 0.505011814
C -13.212548441 2.639140677 0.504993925
C -11.934057148 2.631250135 0.505001124
C -10.655273151 2.628096695 0.504983717
C -9.376861524 2.629562369 0.505014056
C -8.098078606 2.636882829 0.504994802
C -6.819628629 2.647859469 0.504997196
C -5.541017166 2.657794809 0.505001284
C -4.262199583 2.666003307 0.505000350
C -2.983358631 2.674866294 0.504996410
C -1.704642031 2.682927649 0.505005747
C -0.425711088 2.686224288 0.504970561
C 0.852918441 2.684017937 0.504994114
C 2.131876861 2.677086156 0.504990800
C 3.410495116 2.666998386 0.505016462
C 4.689291674 2.657031063 0.505027639
K_POINTS {automatic}
8 1 1 0 0 0
*win.in <http://win.in>*
num_bands = 100
num_wann = 80
num_iter = 100
dis_num_iter = 100
dis_win_max = 8.0
dis_froz_max = 3.5
dis_froz_min = -8.0
guiding_centres = .true.
mp_grid = 8 1 1
iprint = 2
num_dump_cycles = 100
num_print_cycles = 10
transport = true
transport_mode = bulk
one_dim_axis = x
dist_cutoff = 5.5
tran_win_min = -8.5
tran_win_max = 8.5
tran_energy_step = 0.01
fermi_energy = -5.0792
dist_cutoff_mode = one_dim
translation_centre_frac = 0.0 0.0 0.0
bands_plot = true
bands_plot_format = gnuplot
!search_shells = 50
begin kpoint_path
G 0.00000 0.00000 0.00000 F 0.12500 0.00000 0.00000
F 0.12500 0.00000 0.00000 Q 0.25000 0.00000 0.00000
Q 0.25000 0.00000 0.00000 Z 0.35000 0.00000 0.00000
Z 0.35000 0.00000 0.00000 W 0.50000 0.00000 0.00000
W 0.50000 0.00000 0.00000 B 0.75000 0.00000 0.00000
end kpoint_path
begin projections
C:sp3;pz
end projections
begin unit_cell_cart
Ang
20.458886621 0.000000000 0.000000000
0.000000000 25.000000000 0.000000000
0.000000000 0.000000000 25.000000000
end unit_cell_cart
begin atoms_cart
Ang
C -14.491185639 2.648257939 0.505011814
C -13.212548441 2.639140677 0.504993925
C -11.934057148 2.631250135 0.505001124
C -10.655273151 2.628096695 0.504983717
C -9.376861524 2.629562369 0.505014056
C -8.098078606 2.636882829 0.504994802
C -6.819628629 2.647859469 0.504997196
C -5.541017166 2.657794809 0.505001284
C -4.262199583 2.666003307 0.505000350
C -2.983358631 2.674866294 0.504996410
C -1.704642031 2.682927649 0.505005747
C -0.425711088 2.686224288 0.504970561
C 0.852918441 2.684017937 0.504994114
C 2.131876861 2.677086156 0.504990800
C 3.410495116 2.666998386 0.505016462
C 4.689291674 2.657031063 0.505027639
end atoms_cart
Begin KPoints
0.00000000 0.00000000 0.00000000
0.12500000 0.00000000 0.00000000
0.25000000 0.00000000 0.00000000
0.37500000 0.00000000 0.000800000
0.50000000 0.00000000 0.00000000
0.62500000 0.00000000 0.00000000
0.75000000 0.00000000 0.00000000
0.87500000 0.00000000 0.00000000
End KPoints
--
Zeina Salman
PhD Candidate
Microelectronics and Photonics Graduate Program
University of Arkansas
Fayetteville, AR 72701
Office: PHYS 244
Email: zaldolam at email.uark.edu <cxm075 at email.uark.edu>
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