[DFTB-Plus-User] DFTB+NEGF: Net accumulated charge and supercell calculations

Yuranan Hanlumyuang yhanlumyuang at uh.edu
Tue Mar 19 19:37:06 CET 2013

   I have a few more questions about nanowire calculations. I would like to
determine the net accumulated charge
on a nanowire under some applied gate bias.

   (1) I obtained the accumulated charge by summing the net atomic charges
reported in the file 'detailed.out'
With zero bias the accumulated charge is however not zero.   In a normal
SCC calculation,  the accumulated
charge is in the order of 10^-8 - 10 ^-7.  In the GreenFunction case, I got
the net charge of about  -0.001. Is this number
considered insignificant? Is this non-zero charge a result of my choice of
parameters in the Eigensolver (GreenFunction)?

   (2) A cluster geometry is used in the above calculations.  I haven't had
any success with the supercell geometry. I kept getting
message like
   scfsum: 6 NaN NaN NaN

    These messages only appear in supercell calculations. Using the same
input parameters with cluster geometry gives me
no error messages. Is using cluster geometry sufficient for doing a
nanowire calculation?

   Thank you. I am gladful for all guidances I have received  from this
mailing list.

Yuranan Hanlumyuang
University of Houston
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