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Convergence of NEGF for defective GNRs
Date: 2016/10/26 22:04
Name: S Dechamps   <samuel.dechamps@student.uclouvain.be>

Dear all,

I've been trying for a long time to converge a defective nano-ribbon with the following input file. Unfortunately, it is far from convergence, even after 300 iterations (see the bottom for the DFTSCF file). I already tried to change scf.iter.band and increased the number of kpoints. So what could help my system to converge ?

Thanks for your support

########################################
## SCF parameters ##
########################################
scf.EigenvalueSolver NEGF
scf.Min.Mixing.Weight 0.001
scf.energycutoff 500
scf.Max.Mixing.Weight 0.2
scf.maxIter 1400
scf.criterion 1e-11
scf.XcType LSDA-CA
scf.Mixing.History 35
scf.Init.Mixing.Weight 0.02
scf.Mixing.Type rmm-diisk
scf.Mixing.StartPulay 30
scf.ElectronicTemperature 300.0
scf.Mixing.EveryPulay 1
scf.SpinPolarization on
scf.Kgrid 110 1 1
scf.restart off

########################################
## NEGF parameters ##
########################################
NEGF.Poisson.Solver FFT

NEGF.tran.SCF.skip off
NEGF.tran.Analysis on
NEGF.tran.energyrange -2.0 2.0 1.0e-3
NEGF.tran.energydiv 301
NEGF.tran.Kgrid 360 1
NEGF.tran.Channel off # default on

NEGF.filename.hks.l lead.hks
NEGF.filename.hks.r lead.hks
#
NEGF.Num.Poles 100
NEGF.scf.Kgrid 1 1
NEGF.scf.Iter.Band 85
#
NEGF.bias.voltage 0.0
NEGF.bias.neq.energy.step 0.02
NEGF.bias.neq.im.energy 0.01
#
Dos.fileout off
NEGF.Dos.energy.div 301
NEGF.Dos.energyrange -2.0 2.0 5.0e-3
NEGF.Dos.Kgrid 1 1

########################################
## Structure ##
########################################
Atoms.SpeciesAndCoordinates.Unit Ang
LeftLeadAtoms.Number 90
<LeftLeadAtoms.SpeciesAndCoordinates
...
LeftLeadAtoms.SpeciesAndCoordinates>
RightLeadAtoms.Number 90
<RightLeadAtoms.SpeciesAndCoordinates
...
RightLeadAtoms.SpeciesAndCoordinates>
Atoms.Number 150
<Atoms.SpeciesAndCoordinates
...
Atoms.SpeciesAndCoordinates>
Species.Number 2
<Definition.of.Atomic.Species
H H0-s2 H0
C C5.0-s2p2d1 C5.0
Definition.of.Atomic.Species>

---------------------------------------------------------
doing so I get the following DFTSCF file :

***********************************************************
***********************************************************
SCF history at MD= 1
***********************************************************
***********************************************************

SCF= 1 NormRD= 1.000000000000 Uele= 0.000000000000
SCF= 2 NormRD= 46.478114710231 Uele= 0.000000000000
SCF= 3 NormRD= 46.385683944580 Uele= 0.000000000000
SCF= 4 NormRD= 33.143309267105 Uele= 0.000000000000
SCF= 5 NormRD= 27.811408334380 Uele= 0.000000000000
SCF= 6 NormRD= 23.552783787506 Uele= 0.000000000000
SCF= 7 NormRD= 20.200563185816 Uele= 0.000000000000
SCF= 8 NormRD= 17.843545979999 Uele= 0.000000000000
SCF= 9 NormRD= 16.230845998835 Uele= 0.000000000000
SCF= 10 NormRD= 14.985336668306 Uele= 0.000000000000
SCF= 11 NormRD= 13.988382452847 Uele= 0.000000000000
SCF= 12 NormRD= 13.177085074472 Uele= 0.000000000000
SCF= 13 NormRD= 12.505614836807 Uele= 0.000000000000
SCF= 14 NormRD= 11.940184098613 Uele= 0.000000000000
SCF= 15 NormRD= 11.455744007506 Uele= 0.000000000000
SCF= 16 NormRD= 11.033800243063 Uele= 0.000000000000
SCF= 17 NormRD= 10.660649366477 Uele= 0.000000000000
SCF= 18 NormRD= 10.326173331311 Uele= 0.000000000000
SCF= 19 NormRD= 10.022770529569 Uele= 0.000000000000
SCF= 20 NormRD= 9.744808672919 Uele= 0.000000000000
SCF= 21 NormRD= 9.487947891378 Uele= 0.000000000000
SCF= 22 NormRD= 9.248929955858 Uele= 0.000000000000
SCF= 23 NormRD= 9.025120364696 Uele= 0.000000000000
SCF= 24 NormRD= 8.814553270862 Uele= 0.000000000000
SCF= 25 NormRD= 8.615553711519 Uele= 0.000000000000
SCF= 26 NormRD= 8.426851878317 Uele= 0.000000000000
SCF= 27 NormRD= 8.247307997012 Uele= 0.000000000000
SCF= 28 NormRD= 8.076066491631 Uele= 0.000000000000
SCF= 29 NormRD= 7.912298124894 Uele= 0.000000000000
SCF= 30 NormRD= 5.483931446996 Uele= 0.000000000000
SCF= 31 NormRD= 3.380902618035 Uele= 0.000000000000
SCF= 32 NormRD= 3.520544617990 Uele= 0.000000000000
SCF= 33 NormRD= 2.808094103992 Uele= 0.000000000000
SCF= 34 NormRD= 2.232992449847 Uele= 0.000000000000
SCF= 35 NormRD= 1.893491343458 Uele= 0.000000000000
SCF= 36 NormRD= 1.783336417867 Uele= 0.000000000000
SCF= 37 NormRD= 1.596830762009 Uele= 0.000000000000
SCF= 38 NormRD= 1.240133223957 Uele= 0.000000000000
SCF= 39 NormRD= 1.115045485280 Uele= 0.000000000000
SCF= 40 NormRD= 0.946357263332 Uele= 0.000000000000
SCF= 41 NormRD= 1.202445669665 Uele= 0.000000000000
SCF= 42 NormRD= 0.788373356344 Uele= 0.000000000000
SCF= 43 NormRD= 1.061188310647 Uele= 0.000000000000
SCF= 44 NormRD= 0.181697607932 Uele= 0.000000000000
SCF= 45 NormRD= 0.602157522084 Uele= 0.000000000000
SCF= 46 NormRD= 0.232652918996 Uele= 0.000000000000
SCF= 47 NormRD= 0.352448106073 Uele= 0.000000000000
SCF= 48 NormRD= 0.102849827753 Uele= 0.000000000000
SCF= 49 NormRD= 0.076089481166 Uele= 0.000000000000
SCF= 50 NormRD= 0.025305099111 Uele= 0.000000000000
SCF= 51 NormRD= 0.071199199885 Uele= 0.000000000000
SCF= 52 NormRD= 0.062170052791 Uele= 0.000000000000
SCF= 53 NormRD= 0.052423883336 Uele= 0.000000000000
SCF= 54 NormRD= 0.013201141336 Uele= 0.000000000000
SCF= 55 NormRD= 0.017335705369 Uele= 0.000000000000
SCF= 56 NormRD= 0.015739118973 Uele= 0.000000000000
SCF= 57 NormRD= 0.009110481797 Uele= 0.000000000000
SCF= 58 NormRD= 0.007089314053 Uele= 0.000000000000
SCF= 59 NormRD= 0.004484254103 Uele= 0.000000000000
SCF= 60 NormRD= 0.002880517013 Uele= 0.000000000000
SCF= 61 NormRD= 0.001410923665 Uele= 0.000000000000
SCF= 62 NormRD= 0.001040602525 Uele= 0.000000000000
SCF= 63 NormRD= 0.000640872429 Uele= 0.000000000000
SCF= 64 NormRD= 0.000540858259 Uele= 0.000000000000
SCF= 65 NormRD= 0.000479933349 Uele= 0.000000000000
SCF= 66 NormRD= 0.000432524481 Uele= 0.000000000000
SCF= 67 NormRD= 0.000298186879 Uele= 0.000000000000
SCF= 68 NormRD= 0.000131744053 Uele= 0.000000000000
SCF= 69 NormRD= 0.000182606904 Uele= 0.000000000000
SCF= 70 NormRD= 0.000081584066 Uele= 0.000000000000
SCF= 71 NormRD= 0.000092481575 Uele= 0.000000000000
SCF= 72 NormRD= 0.000097447449 Uele= 0.000000000000
SCF= 73 NormRD= 0.000067005348 Uele= 0.000000000000
SCF= 74 NormRD= 0.000044454663 Uele= 0.000000000000
SCF= 75 NormRD= 0.000022123615 Uele= 0.000000000000
SCF= 76 NormRD= 0.000012423453 Uele= 0.000000000000
SCF= 77 NormRD= 0.000007907606 Uele= 0.000000000000
SCF= 78 NormRD= 0.000005808727 Uele= 0.000000000000
SCF= 79 NormRD= 0.000010219875 Uele= 0.000000000000
SCF= 80 NormRD= 0.000004279514 Uele= 0.000000000000
SCF= 81 NormRD= 0.000002568054 Uele= 0.000000000000
SCF= 82 NormRD= 0.000001076456 Uele= 0.000000000000
SCF= 83 NormRD= 0.000000742021 Uele= 0.000000000000
SCF= 84 NormRD= 0.000000408055 Uele= 0.000000000000
SCF= 85 NormRD= 0.000000266408 Uele= 0.000000000000
SCF= 86 NormRD= 10.093133746743 Uele= 0.000000000000
SCF= 87 NormRD= 10.093133714317 Uele= 0.000000000000
SCF= 88 NormRD= 10.093133713732 Uele= 0.000000000000
SCF= 89 NormRD= 10.093133717178 Uele= 0.000000000000
SCF= 90 NormRD= 10.093133716662 Uele= 0.000000000000
SCF= 91 NormRD= 10.093133716075 Uele= 0.000000000000
SCF= 92 NormRD= 10.093133716203 Uele= 0.000000000000
SCF= 93 NormRD= 10.093133718807 Uele= 0.000000000000
SCF= 94 NormRD= 10.093133718326 Uele= 0.000000000000
SCF= 95 NormRD= 10.093133718418 Uele= 0.000000000000
SCF= 96 NormRD= 10.093133720144 Uele= 0.000000000000
SCF= 97 NormRD= 10.093133718599 Uele= 0.000000000000
SCF= 98 NormRD= 10.093133717081 Uele= 0.000000000000
SCF= 99 NormRD= 10.093133719222 Uele= 0.000000000000
SCF= 100 NormRD= 10.093133717344 Uele= 0.000000000000
SCF= 101 NormRD= 10.093133708141 Uele= 0.000000000000
SCF= 102 NormRD= 10.093133709043 Uele= 0.000000000000
SCF= 103 NormRD= 10.093133709027 Uele= 0.000000000000
SCF= 104 NormRD= 10.093133708917 Uele= 0.000000000000
SCF= 105 NormRD= 10.093133709875 Uele= 0.000000000000
SCF= 106 NormRD= 10.093133709454 Uele= 0.000000000000
SCF= 107 NormRD= 10.093133712167 Uele= 0.000000000000
SCF= 108 NormRD= 10.093133709942 Uele= 0.000000000000
SCF= 109 NormRD= 10.093133711058 Uele= 0.000000000000
SCF= 110 NormRD= 10.093133713086 Uele= 0.000000000000
SCF= 111 NormRD= 10.093133718940 Uele= 0.000000000000
SCF= 112 NormRD= 10.093133719725 Uele= 0.000000000000
SCF= 113 NormRD= 10.093133716709 Uele= 0.000000000000
SCF= 114 NormRD= 10.093133717437 Uele= 0.000000000000
SCF= 115 NormRD= 10.093133717464 Uele= 0.000000000000
SCF= 116 NormRD= 10.093133716435 Uele= 0.000000000000
SCF= 117 NormRD= 10.093133715953 Uele= 0.000000000000
SCF= 118 NormRD= 10.093133717719 Uele= 0.000000000000
SCF= 119 NormRD= 10.093133698329 Uele= 0.000000000000
SCF= 120 NormRD= 10.093133699615 Uele= 0.000000000000
SCF= 121 NormRD= 27.966167920378 Uele= 0.000000000000
SCF= 122 NormRD= 17.916020762704 Uele= 0.000000000000
SCF= 123 NormRD= 18.852540694857 Uele= 0.000000000000
SCF= 124 NormRD= 19.000454257806 Uele= 0.000000000000
SCF= 125 NormRD= 21.142854189847 Uele= 0.000000000000
SCF= 126 NormRD= 16.360295527617 Uele= 0.000000000000
SCF= 127 NormRD= 18.991980205105 Uele= 0.000000000000
SCF= 128 NormRD= 16.290463253540 Uele= 0.000000000000
SCF= 129 NormRD= 19.794446868427 Uele= 0.000000000000
SCF= 130 NormRD= 31.146319848341 Uele= 0.000000000000
SCF= 131 NormRD= 40.906120446304 Uele= 0.000000000000
SCF= 132 NormRD= 26.190558171213 Uele= 0.000000000000
SCF= 133 NormRD= 22.701039028918 Uele= 0.000000000000
SCF= 134 NormRD= 23.678128178593 Uele= 0.000000000000
SCF= 135 NormRD= 22.677952861645 Uele= 0.000000000000
SCF= 136 NormRD= 22.701437064188 Uele= 0.000000000000
SCF= 137 NormRD= 22.339972128220 Uele= 0.000000000000
SCF= 138 NormRD= 22.209097259352 Uele= 0.000000000000
SCF= 139 NormRD= 21.481955150498 Uele= 0.000000000000
SCF= 140 NormRD= 23.189412401123 Uele= 0.000000000000
SCF= 141 NormRD= 22.802836379700 Uele= 0.000000000000
SCF= 142 NormRD= 23.001679032635 Uele= 0.000000000000
SCF= 143 NormRD= 22.745196327973 Uele= 0.000000000000
SCF= 144 NormRD= 22.621748995811 Uele= 0.000000000000
SCF= 145 NormRD= 22.653729373076 Uele= 0.000000000000
SCF= 146 NormRD= 22.547278020968 Uele= 0.000000000000
SCF= 147 NormRD= 22.693071058624 Uele= 0.000000000000
SCF= 148 NormRD= 22.699471634709 Uele= 0.000000000000
SCF= 149 NormRD= 22.627587837344 Uele= 0.000000000000
SCF= 150 NormRD= 23.396385300927 Uele= 0.000000000000
SCF= 151 NormRD= 23.166344420548 Uele= 0.000000000000
SCF= 152 NormRD= 23.156504533489 Uele= 0.000000000000
SCF= 153 NormRD= 23.156975225255 Uele= 0.000000000000
SCF= 154 NormRD= 23.088537096199 Uele= 0.000000000000
SCF= 155 NormRD= 23.054534612239 Uele= 0.000000000000
SCF= 156 NormRD= 24.447811951672 Uele= 0.000000000000
SCF= 157 NormRD= 25.263147797112 Uele= 0.000000000000
SCF= 158 NormRD= 24.627560777335 Uele= 0.000000000000
SCF= 159 NormRD= 23.006612878052 Uele= 0.000000000000
SCF= 160 NormRD= 27.754068938840 Uele= 0.000000000000
SCF= 161 NormRD= 22.870664035900 Uele= 0.000000000000
SCF= 162 NormRD= 22.951697277094 Uele= 0.000000000000
SCF= 163 NormRD= 24.803857493634 Uele= 0.000000000000
SCF= 164 NormRD= 23.784994927406 Uele= 0.000000000000
SCF= 165 NormRD= 27.400255268979 Uele= 0.000000000000
SCF= 166 NormRD= 31.904069611016 Uele= 0.000000000000
SCF= 167 NormRD= 27.950600022073 Uele= 0.000000000000
SCF= 168 NormRD= 38.781295116791 Uele= 0.000000000000
SCF= 169 NormRD= 33.272122549049 Uele= 0.000000000000
SCF= 170 NormRD= 28.003184748957 Uele= 0.000000000000
SCF= 171 NormRD= 30.338556493037 Uele= 0.000000000000
SCF= 172 NormRD= 31.007966899478 Uele= 0.000000000000
SCF= 173 NormRD= 27.666810103419 Uele= 0.000000000000
SCF= 174 NormRD= 28.598941019926 Uele= 0.000000000000
SCF= 175 NormRD= 27.028362696200 Uele= 0.000000000000
SCF= 176 NormRD= 26.768092808540 Uele= 0.000000000000
SCF= 177 NormRD= 27.544251283809 Uele= 0.000000000000
SCF= 178 NormRD= 25.759151255315 Uele= 0.000000000000
SCF= 179 NormRD= 26.583991400775 Uele= 0.000000000000
SCF= 180 NormRD= 26.836915154167 Uele= 0.000000000000
SCF= 181 NormRD= 26.962787956940 Uele= 0.000000000000
SCF= 182 NormRD= 27.732072649313 Uele= 0.000000000000
SCF= 183 NormRD= 28.727295705107 Uele= 0.000000000000
SCF= 184 NormRD= 26.411012612307 Uele= 0.000000000000
SCF= 185 NormRD= 25.400427299415 Uele= 0.000000000000
SCF= 186 NormRD= 25.524892350950 Uele= 0.000000000000
SCF= 187 NormRD= 27.412863617159 Uele= 0.000000000000
SCF= 188 NormRD= 27.342019311136 Uele= 0.000000000000
SCF= 189 NormRD= 26.793217665616 Uele= 0.000000000000
SCF= 190 NormRD= 26.863376721287 Uele= 0.000000000000
SCF= 191 NormRD= 27.558541751097 Uele= 0.000000000000
SCF= 192 NormRD= 27.666929219970 Uele= 0.000000000000
SCF= 193 NormRD= 27.340069196212 Uele= 0.000000000000
SCF= 194 NormRD= 27.953445898208 Uele= 0.000000000000
SCF= 195 NormRD= 29.359922451185 Uele= 0.000000000000
SCF= 196 NormRD= 26.944637421547 Uele= 0.000000000000
SCF= 197 NormRD= 26.893222402533 Uele= 0.000000000000
SCF= 198 NormRD= 28.072016677498 Uele= 0.000000000000
SCF= 199 NormRD= 31.867109783702 Uele= 0.000000000000
SCF= 200 NormRD= 30.602226468585 Uele= 0.000000000000
SCF= 201 NormRD= 30.629991114227 Uele= 0.000000000000
SCF= 202 NormRD= 29.295745951030 Uele= 0.000000000000
SCF= 203 NormRD= 30.863125239213 Uele= 0.000000000000
SCF= 204 NormRD= 31.342832557849 Uele= 0.000000000000
SCF= 205 NormRD= 33.019797085468 Uele= 0.000000000000
SCF= 206 NormRD= 33.200085976226 Uele= 0.000000000000
SCF= 207 NormRD= 32.286977219190 Uele= 0.000000000000
...
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Re: Convergence of NEGF for defective GNRs ( No.1 )
Date: 2016/10/27 18:27
Name: Artem Pulkin

Following are my suggestions:

1. Having 110 k-points does not really matter. You may decrease it down to 10-1 k-point for sure.

2. I guess you have a charge sloshing problem. To check it, look if the occupation numbers go bananas (unphysically low or high) at 121st iteration and after. Set Kerker factor to something large to avoid it. I set

scf.Kerker.factor 35

for a 6-7 nm long scattering region. It does not look like you have that long system so you may try above value. Generally, larger - better (though there are drawbacks, ofc).

3. Try delaying the start of Pulay mixing by a few iterations. For example, I use the following combination:

NEGF.scf.Iter.Band 40
scf.Mixing.History 40
scf.Mixing.StartPulay 90

Here, I waive converged charged density for periodic boundary conditions: looking at your NormRD values it does not really help (same was in my case). Instead, I get a better history to start the Pulay mixing.

4. Finally, you may have to increase your scattering region. But I really encourage you to try cooking a proper mixing scheme because the computation times for a larger system will explode.
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Re: Convergence of NEGF for defective GNRs ( No.2 )
Date: 2016/10/28 15:37
Name: T. Ozaki

Hi,

While something happens at SCF=86,


SCF= 85 NormRD= 0.000000266408 Uele= 0.000000000000
SCF= 86 NormRD= 10.093133746743 Uele= 0.000000000000


the value of NormRD at SCF=85 is already enough to consider the calculation is convergent.
NormRD of 10^{-6} might be enough for transport calculations in most cases.

Regards,

TO
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Re: Convergence of NEGF for defective GNRs ( No.3 )
Date: 2016/10/28 18:07
Name: Artem Pulkin

At SCF=86 the periodic boundary conditions were replaced by the fixed ones.

NEGF.scf.Iter.Band 85

To the best of my knowledge, in older versions of OpenMX the charge density obtained at this step is not physical (because off-diagonal coupling terms in the Hamiltonian were neglected for simplicity, I guess). I believe one cannot use this Hamiltonian for transport calculations. It is easy to check it on an ideal nanowire model.

Artem
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Re: Convergence of NEGF for defective GNRs ( No.4 )
Date: 2016/11/07 19:58
Name: Vipin Kumar

Dear all,

This problem frequently occurs when we run the NEGF calculation. In NEGF calculation, the NormRD, after the completion of NEGF.SCF.Iter.Band steps, increases suddenly in most of the cases. Similar problem, I am also facing. I want to ask that, is there any simple way or a proper route to avoid this problem. We can play with Mixing parameters, no doubt, but is there any way to choose proper mixing scheme to avoid it in less time and less effort. How to pick the proper mixing scheme. Any help would be highly appreciated.

Thanks.
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Re: Convergence of NEGF for defective GNRs ( No.5 )
Date: 2016/11/08 23:02
Name: Artem Pulkin

"I want to ask that, is there any simple way or a proper route to avoid this problem."

If you think it is a problem, just set

NEGF.SCF.Iter.Band 0
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Re: Convergence of NEGF for defective GNRs ( No.6 )
Date: 2016/11/10 20:07
Name: S Dechamps  <samuel.dechamps@student.uclouvain.be>

Dear all,

setting :

NEGF.scf.Iter.Band 40
scf.Mixing.History 40
scf.Mixing.StartPulay 90

(note that the Kerker factor was set automatically to 20.5)

worked just fine for me.

Thanks a lot for the help,
Best
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