No current in NEGF calculation

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No current in NEGF calculation

Date: 2017/04/10 13:42
Name: Bill Guo: Hello all,

I am trying to calculate current and conductance through stacked NbS2 and MoS2 layers. An illustration of the system:

-> || || || ->
-> || || || -> current direction
-> || || || ->
NbS2 MoS2 NbS2

My calculation finishes successfully but I see 0 current and no conductance. What could be the problem?

My input file:
##########################################################################################
#
# File Name
#

System.CurrrentDirectory ./ # default=./
System.Name negf-mos2-nbs2
level.of.stdout 1 # default=1 (1-3)
level.of.fileout 0 # default=1 (0-2)

NEGF.filename.hks.l lead-nbs2-l.hks
NEGF.filename.hks.r lead-nbs2-r.hks

NEGF.Num.Poles 150 # default=150
NEGF.scf.Kgrid 1 1 # default=1 1
NEGF.SCF.Iter.Band 10

NEGF.bias.voltage -1.0 # default=0.0 (eV)
NEGF.bias.neq.im.energy 0.01 # default=0.01 (eV)
NEGF.bias.neq.energy.step 0.02 # default=0.02 (eV)

NEGF.gate.voltage -16.0

Dos.fileout off # on|off, default=off
NEGF.Dos.energyrange -15.0 25.0 5.0e-3 #default=-10.0 10.0 5.0e-3 (eV)
NEGF.Dos.energy.div 200 # default=200
NEGF.Dos.Kgrid 1 1 # default=1 1

NEGF.tran.energydiv 200 # default=200
NEGF.tran.energyrange -10 10 1.0e-3 # default=-10.0 10.0 1.0e-3 (eV)
NEGF.tran.Kgrid 1 1 # default= 1 1

#
# Definition of Atomic Species
#

Species.Number 3
<Definition.of.Atomic.Species
Mo Mo7.0-s2p2d2 Mo_CA13
Nb Nb7.0-s2p2d2 Nb_CA13
S S7.0-s2p2d2 S_CA13
Definition.of.Atomic.Species>

#
# Atoms
#

Atoms.SpeciesAndCoordinates.Unit Ang # Ang|AU

Atoms.Number 12
<Atoms.SpeciesAndCoordinates
1 Mo 1.594199831 2.761235530 11.927202344 7.0 7.0
2 Mo 0.000000000 0.000000000 11.927202344 7.0 7.0
3 Mo 4.782599861 2.761235530 11.927202344 7.0 7.0
4 Mo 3.188400030 0.000000000 11.927202344 7.0 7.0
5 S 3.188400003 1.840823741 10.365363210 3.0 3.0
6 S 4.782599929 4.602059436 10.365363210 3.0 3.0
7 S 6.376800223 1.840823741 10.365363210 3.0 3.0
8 S 7.971000149 4.602059436 10.365363210 3.0 3.0
9 S 3.188400003 1.840823741 13.488271832 3.0 3.0
10 S 4.782599929 4.602059436 13.488271832 3.0 3.0
11 S 6.376800223 1.840823741 13.488271832 3.0 3.0
12 S 7.971000149 4.602059436 13.488271832 3.0 3.0
Atoms.SpeciesAndCoordinates>

#
# Lead-Left
#

LeftLeadAtoms.Number 12
<LeftLeadAtoms.SpeciesAndCoordinates # Unit=Ang.
1 Nb 1.679300144 2.908632724 5.427004769 6.5 6.5
2 Nb 0.000000000 0.000000000 5.427004769 6.5 6.5
3 Nb 5.037900045 2.908632724 5.427004769 6.5 6.5
4 Nb 3.358599901 0.000000000 5.427004769 6.5 6.5
5 S 3.358600130 1.939088540 3.866012022 3.0 3.0
6 S 5.037900375 4.847721437 3.866012022 3.0 3.0
7 S 6.717200232 1.939088540 3.866012022 3.0 3.0
8 S 8.396500476 4.847721437 3.866012022 3.0 3.0
9 S 3.358600130 1.939088540 6.987820566 3.0 3.0
10 S 5.037900375 4.847721437 6.987820566 3.0 3.0
11 S 6.717200232 1.939088540 6.987820566 3.0 3.0
12 S 8.396500476 4.847721437 6.987820566 3.0 3.0
LeftLeadAtoms.SpeciesAndCoordinates>

#
# Lead-Right
#

RightLeadAtoms.Number 12
<RightLeadAtoms.SpeciesAndCoordinates # Unit=Ang.
1 Nb 1.679300144 2.908632724 18.427202106 6.5 6.5
2 Nb 0.000000000 0.000000000 18.427202106 6.5 6.5
3 Nb 5.037900045 2.908632724 18.427202106 6.5 6.5
4 Nb 3.358599901 0.000000000 18.427202106 6.5 6.5
5 S 3.358600130 1.939088540 16.865363717 3.0 3.0
6 S 5.037900375 4.847721437 16.865363717 3.0 3.0
7 S 6.717200232 1.939088540 16.865363717 3.0 3.0
8 S 8.396500476 4.847721437 16.865363717 3.0 3.0
9 S 3.358600130 1.939088540 19.988271594 3.0 3.0
10 S 5.037900375 4.847721437 19.988271594 3.0 3.0
11 S 6.717200232 1.939088540 19.988271594 3.0 3.0
12 S 8.396500476 4.847721437 19.988271594 3.0 3.0
RightLeadAtoms.SpeciesAndCoordinates>

#
# SCF or Electronic System
#

scf.XcType GGA-PBE # LDA|LSDA-CA|LSDA-PW|GGA-PBE
scf.SpinPolarization off # On|Off|NC
scf.ElectronicTemperature 300.0 # default=300 (K)
scf.energycutoff 180.0 # default=150 (Ry)
scf.maxIter 100 # default=40
scf.EigenvalueSolver NEGF # DC|GDC|Cluster|Band
scf.lapack.dste dstevx # dstegr|dstedc|dstevx, default=dstegr
scf.Kgrid 1 1 1 # means n1 x n2 x n3
scf.Mixing.Type rmm-diisk # Simple|Rmm-Diis|Gr-Pulay|Kerker|Rmm-Diisk
scf.Init.Mixing.Weight 0.020 # default=0.30
scf.Min.Mixing.Weight 0.020 # default=0.001
scf.Max.Mixing.Weight 0.100 # default=0.40
scf.Mixing.History 20 # default=5
scf.Mixing.StartPulay 10 # default=6
scf.Kerker.factor 1.0 # default=1.0
scf.criterion 1.0e-7 # default=1.0e-6 (Hartree)
##########################################################################################

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Re: No current in NEGF calculation ( No.1 )

Date: 2017/04/11 15:21
Name: Fronquer

Dear Guo,

As I can observe from your input file, I think you forget the following tags to add in your NEGF file

NEGF.tran.Analysis on

NEGF.tran.CurrentDensity on

NEGF.tran.Channel on

Re: No current in NEGF calculation ( No.2 )

Date: 2017/04/11 18:24
Name: Bill Guo

Incredible. It's always the tiny things. Thanks so much Fronquer! Hopefully there are no other issues.

Re: No current in NEGF calculation ( No.3 )

Date: 2017/04/12 07:18
Name: Bill Guo

Actually those settings default to on, if I'm not mistaken? I get the same results with those lines. Still 0 current.

Re: No current in NEGF calculation ( No.4 )

Date: 2017/04/12 18:26
Name: T. Ozaki

Hi,

Did you check the transmission and confirm that the source-drain
bias window overlaps with the energy range of non-zero transmission?
Also, I've noticed that you applied a very large gate voltage for
such a narrow region, and been wondering that this may cause
an unphysical charge transfer between C0 and L0(R0) regions, resulting
in a physically unacceptable result.

Regards,

TO

Re: No current in NEGF calculation ( No.5 )

Date: 2017/04/12 18:42
Name: Artem Pulkin

Yep, 16 Volts per less than nm is unphyscial. Even for larger scattering regions, it does not make sense to probe valence or conduction states that are 16 eV away from the Fermi level: this value is much larger than the vacuum level in MoS2.

Re: No current in NEGF calculation ( No.6 )

Date: 2017/04/19 16:25
Name: Bill Guo

Hi Dr. Ozaki and Dr. Pulkin,

Thanks for your input. I have tried using 4V gate voltage and source-drain voltage of 2 and 3V, which should overlap with the non-zero transmission range. But nevertheless in every scenario I see no current, which seems bizarre. Which leads me to think that there is something else wrong with my parameter specifications, besides the voltages?

Re: No current in NEGF calculation ( No.7 )

Date: 2017/04/20 13:20
Name: T. Ozaki

Hi,

It would be better to check one by one.
Could you check the transmission and DOS of NbS2 bulk and MoS2 bulk,
respectively? Then, could you check PDOS of NbS2 and MoS2 in the device
configuration under zero bias voltage for both gate and source-drain
if the PDOS in the device resembles the bulk couterpart?
If this is what you expect, you can apply bias voltage to see how the
PDOS and transmission are altered under finite voltages.

Regards,

TO

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