[DFTB-Plus-User] Cannot calculate transport
Argo
argo.nurbawono at gmail.com
Wed Apr 15 14:13:58 CEST 2015
hi.
i have never used dftb-negf program, but i have some experience in
calculating density matrix from negf green function technique for
transport calculations (dft+negf variant).
there are many many ways that the countour integral can fail in negf,
and your problem does not seem to have anything to do with the way you
compile the program- it is purely numerical issue. your program may be
just fine.
the green function has a small imaginary part (i*eta) that if the
default value is set too small, it will show strong singularity in the
inversion process. so maybe you can try increasing eta (wherever that is
in the dftb-negf input file) by 1 order magnitude. i dont know how that
is set in dftb input file, but it should be there.
you can try a small number of contour point first for the first try, and
then increase the contour point gradually to look for convergence.
you can try applying a finite bias voltage. often zero bias poses
problems in negf calculations, and there is a minimal bias you need to
apply in order to make the matrix invertible.
if you want "zero" bias, people usually take 0.02 volts or something
like that to mimic zero bias.
if the calculation crashes at a particular bias (eg. 0.2 volts), you can
try increasing/decreasing the bias by a small weird value (eg. to 0.203
or 0.197).
additionally you can also try increasing the electronic temperature
(smearing).
good luck.
On Wed, 2015-04-15 at 13:47 +0200, Alessandro Pirrotta wrote:
> Dear DFTB+ users,
>
>
> I have compiled and successfully tested (with autotest) dftb+mpi-negf.
>
>
> I have then run a drain, source and device calculation.
> Drain and source run fine, but then the device calculation crashes
> giving this output:
>
>
> Reading SKF file
> ....
> .....
> Done.
>
>
> Processed input in HSD format written to 'dftb_pin.hsd'
>
>
> Starting initialization...
> --------------------------------------------------------------------------------
> PGRID:ALLPROC: 1 x 1
> PGRID:ATOM: 1 x 1
> Poisson parallelized on 1 nodes
> Atomic density tolerance: 1.000000000000000E-005
> Atomic density cutoff: 9.39669825812203 a.u.
> Input PoissonBox= 30.0000 30.0000 30.0000 A
> PoissAcc= 1.000000000000000E-007
> Bulk Boundary Potential: No
> Atomic cutoff radius= 4.97251893391611 A
>
>
> CENTRAL REGION
> Atom start - end = 1 22
>
>
> CONTACT # 1
> Atom start - end = 23 118
> direction: 3
> Fermi Level= -4.70500000000000 eV
> mu= 0.136056922500000 V
>
>
> CONTACT # 2
> Atom start - end = 119 214
> direction: -3
> Fermi Level= -4.70500000000000 eV
> mu= -0.136056922500000 V
>
>
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> INIT MPI-NEGF ON 1 NODES
> CPU 0 READY
> PRINTING CPU: T
> Mode: Static calculation
> Contact upload: Yes
> Contact calculation: No
> Use Poisson solver: Yes
> Self consistent charges: Yes
> SCC-tolerance: 0.100000E-06
> Max. scc iterations: 2000
> Ewald alpha parameter: 0.000000E+00
> Spin polarisation: No
> Nr. of up electrons: 1091.000000
> Nr. of down electrons: 1091.000000
> Periodic boundaries: No
> Diagonalizer: Green's Functions (density matrix)
> Maximal SCC-cycles: 2000
> Electronic temperature: 0.100000E-07
> Initial charges: Set automatically (system chrg: 0.000E
> +00)
> Included shells: S: s, p, d
> C: s, p
> O: s, p
> H: s
> Au: s, p, d
> Extra options:
> --------------------------------------------------------------------------------
>
>
> ********************************************************************************
> ** Geometry step: 0
> ********************************************************************************
>
>
> MAXNEIGHBORS: 161
> Structure info:
> Number of PLs: 1
> Interacting PLs: 1 1
>
>
> iSCC Total electronic Diff electronic SCC error
> =========================================================================
> SOLVING POISSON EQUATION
> =========================================================================
> -------------------------------------------------------------------------
> Poisson Box internally adjusted:
> x range= -14.93910 15.06090; Periodic: F
> y range= -15.02760 14.97240; Periodic: F
> z range= -3.14441 15.18553; Periodic: F
> Mesh details:
> Lx= 30.000 nx= 129 dlx= 0.23437
> Ly= 30.000 ny= 129 dly= 0.23437
> Lz= 18.330 nz= 65 dlz= 0.28641
> -------------------------------------------------------------------------
> -------------------------------------------------------------------------
> Relative Poisson Error = 1.952627165542703E-008
> Number of cycles executed = 8/ 60
> -------------------------------------------------------------------------
> *************************************************************************
> =========================================================================
> COMPUTING DENSITY MATRIX
> =========================================================================
> CONTOUR INTEGRATION:*** 70 points
> srun: error: node244: task 0: Segmentation fault (core dumped)
> srun: Terminating job step 615175.0
>
>
> I have compiled it with mpif90, ifort 13.0.1, and openmpi-1.6.5-i4
> Any idea why the tests run fine and this does not?
>
>
> Kind regards,
> Alessandro
>
>
> Alessandro Pirrotta
> PhD student
>
>
>
> Faculty of Science
> Department of Chemistry &
> Nano-Science Center
> University of Copenhagen
> Universitetsparken 5, C321
> 2100 Copenhagen Ø
> Denmark
>
> DIR +45 21 18 11 90
> MOB +45 52 81 23 41
>
>
>
> alessandro.pirrotta at chem.ku.dk
>
> alessandro.pirrotta at gmail.com
>
>
> www.ki.ku.dk
>
>
>
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