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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. 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 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 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. 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 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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