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Difficult to get converge in spin polarized NEGF calculation
Date: 2015/09/17 01:54
Name: Pang   <pangr@sustc.edu.cn>

Dear all, I am trying to calcluate a STM system consisted of Ni, Cu, Co and organic pieces,300 atoms. The normal SCF get converged,and the electronic structures are well coincide with other code. but in NEGF, the SCF process does not converge, the following is the SCF parameters I used. Could anyone give me any suggestion?

scf.XcType GGA-PBE # LDA|LSDA-CA|LSDA-PW
scf.SpinPolarization on # On|Off
scf.ElectronicTemperature 1000.0 # default=300 (K)
scf.energycutoff 350.0 # default=150 (Ry)
scf.maxIter 300 # default=40
scf.EigenvalueSolver NEGF # Recursion|Cluster|Band
scf.Kgrid 1 3 3 # means n1 x n2 x n3
scf.Mixing.Type RMM-DIISK # Simple|Rmm-Diis|Gr-Pulay
scf.Init.Mixing.Weight 0.00010 # default=0.30
scf.Min.Mixing.Weight 0.00001 # default=0.001
scf.Max.Mixing.Weight 0.01 # default=0.40
scf.Mixing.History 60 # default=5
scf.Mixing.StartPulay 80 # default=6
#scf.criterion 1.0e-6 # default=1.0e-6 (Hartree)
scf.Mixing.EveryPulay 1
scf.Kerker.factor 50
#
# restart using *.rst
#

scf.restart off # on|off, default=off
NEGF.filename.hks.l lead1.hks
NEGF.filename.hks.r lead2.hks

NEGF.Num.Poles 100 # defalut=150
NEGF.scf.Kgrid 3 3 # defalut=1 1
NEGF.scf.Iter.Band 300
NEGF.bias.voltage 0.0 # 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)

Dos.fileout on # on|off, default=off
NEGF.Dos.energyrange -20.0 20.0 1.0e-4 #default=-10.0 10.0 5.0e-3 (eV)
NEGF.Dos.energy.div 3000 # default=200
NEGF.Dos.Kgrid 3 3 # default=1 1

NEGF.tran.energydiv 200 # default=200
NEGF.tran.energyrange -4 4 0.001 # default=-10.0 10.0 5.0e-3 (eV)
NEGF.tran.Kgrid 3 3 # default= 1 1


There are some additional information. The total magnetic moment of the system should be less than 86 muB. But I can see from the output that, before starting Pulay mixing, the Total Spin Moment increased from 8 to 130, after that, the Total Spin Moment vibrated around 100 muB. When I switched the NEGF.Poisson.Solver to FD, the Total Spin Moment became 0 muB and vibrated around 0 until the end. Is this normal?
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