Top Page > Browsing

Convergence of NEGF in heterostructure Date: 2017/01/04 20:13 Name: S Dechamps   <samuel.dechamps@student.uclouvain.be> Dear all, I'm currently trying to converge a system made of two semi-infinite sheets of graphene, coupled by van der waals interaction (VdW-D3) : left lead central device right lead ----------|---------------- | | ----------------|------------- Nevertheless, the NEGF computations is not converging, even after 3000 iterations; with normRD remaining larger than 0.09, with cyclic variations between 0.09 and 10 (so no monotonically decreasing behavior). Regarding your previous advice for my charge sloshing problem (http://www.openmx-square.org/forum/patio.cgi?mode=view&no=2035), I already put in this case : scf.Mixing.History 40 scf.Mixing.StartPulay 90 as you can see, with no result for the convergence How could I attain a converged NEGF computation ? Best, S. Dechamps The input file is the following : ######################################## ## SCF parameters ## ######################################## scf.EigenvalueSolver NEGF scf.Min.Mixing.Weight 0.001 scf.energycutoff 500 scf.Max.Mixing.Weight 0.2 scf.maxIter 36000 scf.criterion 1e-09 scf.XcType GGA-PBE scf.Mixing.History 40 scf.Init.Mixing.Weight 0.02 scf.Mixing.Type rmm-diisk scf.Mixing.StartPulay 90 scf.ElectronicTemperature 300.0 scf.Mixing.EveryPulay 1 scf.SpinPolarization on scf.Kgrid 36 48 1 scf.restart off ######################################## ## MD parameters ## ######################################## MD.Type nomd MD.TimeStep 0.5 MD.maxIter 1 MD.Opt.criterion 0.0001 ######################################## ## NEGF parameters ## ######################################## NEGF.tran.SCF.skip off NEGF.Poisson.Solver FFT NEGF.tran.Analysis on NEGF.tran.energyrange -1.0 1.0 1.0e-3 NEGF.tran.energydiv 101 NEGF.tran.Kgrid 480 1 NEGF.tran.Channel off # default on NEGF.Channel.Nkpoint 1 # default=1 <NEGF.Channel.kpoint 0.0 0.0 NEGF.Channel.kpoint> NEGF.Channel.Nenergy 1 # default=1 <NEGF.Channel.energy 0.0 NEGF.Channel.energy> NEGF.Channel.Num 3 # defualt=5(for collinear), 10(for Non-collinear) NEGF.tran.CurrentDensity on NEGF.filename.hks.l lead-LL_C.hks NEGF.filename.hks.r lead-RL_C.hks NEGF.Num.Poles 100 NEGF.scf.Kgrid 48 1 NEGF.scf.Iter.Band 30 NEGF.bias.voltage 0.0 NEGF.bias.neq.energy.step 0.02 NEGF.bias.neq.im.energy 0.01 ######################################## ## Structure ## ######################################## Atoms.SpeciesAndCoordinates.Unit Ang LeftLeadAtoms.Number 8 <LeftLeadAtoms.SpeciesAndCoordinates ... LeftLeadAtoms.SpeciesAndCoordinates> RightLeadAtoms.Number 8 <RightLeadAtoms.SpeciesAndCoordinates ... RightLeadAtoms.SpeciesAndCoordinates> Atoms.Number 40 <Atoms.SpeciesAndCoordinates ... Atoms.SpeciesAndCoordinates> Species.Number 1 <Definition.of.Atomic.Species C C5.0_GGA-s2p2d1 C5.0_GGA Definition.of.Atomic.Species> ######################################## ## VdW ## ######################################## scf.dftD on # on|off, default=off version.dftD 3 # 2|3, default=2 DFTD3.damp zero # zero|bj, default=bj DFTD.IntDirection 1 1 0 # default=1 1 1 (1:on 0:off)

Page: [1]

Re: Convergence of NEGF in heterostructure ( No.1 ) Date: 2017/01/04 20:20 Name: S Dechamps  <samuel.dechamps@student.uclouvain.be> For the sake of clarity, I repost the scheme of the L|C|R system : | left lead | central device | right lead | |-----------|----------------| | | |----------------|------------| with ---- being an atomically thin layer Re: Convergence of NEGF in heterostructure ( No.2 ) Date: 2017/01/05 18:27 Name: Artem Pulkin Well, as far as I can understand you miss the purpose of the 'central device'. Your system should rather be [left]|-----central----- | | ------device-----|[right] I.e. the edge of the top graphene layer cannot be right above the right lead. Similarly, the edge of the bottom layer cannot be right below the left lead. Both terminations should be away from the leads as much as it is possible. The FFT solver makes no sense in this system either. Re: Convergence of NEGF in heterostructure ( No.3 ) Date: 2017/01/05 18:31 Name: Artem Pulkin The pseudo-image was trimmed. The correct one is: [=left=]|=====central=====-----|--------- --------|-----======device=====|[=right=] '-' corresponds to vacuum '=' is atomic monolayer Re: Convergence of NEGF in heterostructure ( No.4 ) Date: 2017/01/05 19:10 Name: S Dechamps  <samuel.dechamps@student.uclouvain.be> Same for my pseudo-image, my device is such as yours : [=left=]|=====central=====-----|--------- --------|-----======device=====|[=right=] '-' corresponds to vacuum '=' is atomic monolayer with an overlap region of about 2nm Re: Convergence of NEGF in heterostructure ( No.5 ) Date: 2017/01/05 19:39 Name: Artem Pulkin Well, than the periodic form of the potential screwed up your calculation. What is the total size of the central region? Re: Convergence of NEGF in heterostructure ( No.6 ) Date: 2017/01/05 20:16 Name: S Dechamps  <samuel.dechamps@student.uclouvain.be> It is the overlap region, plus a conventional cell of graphene on each interface with the leads, so a bit less than 3nm in total.

Page: [1]