[DFTB-Plus-User] NEGF: IV curve

[Gabriele Penazzi]

Hi Michael,

the default unit for the bias in the input file is Hartree (we borrow
energy units to be consistent with the rest of input), see manual. If
you want to apply V you have to specify [eV] after the potential
keyword.  Therefore you're applying 0.2H=5.4V, not 0.2V as you think.
Considering this, the conductance look fine and you're being able to
converge at quite high bias.

I don't know what happens at 0.1H, but if you go to quite large bias you
should maybe check you're electrostatic (is the device still long enough
to let the potential relax correctly) and understand better if you step
in some event which may change your device behaviour (e.g. crossing
other bands, injecting charge in defect states etc.)

Best
Gabriele




On 04/23/2015 02:05 AM, Michael Foster wrote:
> Hi,
>
> I'm trying to predict an IV curve for a 10,10-CNT but the result I'm
> getting seems a little strange (see Fig. below). Why is the current
> flatting out and even slightly decreasing as the drain voltage is
> increased?  For the calculations, the source voltage is constant (0 V)
> and I'm simply increasing the drain voltage in 0.01 V increments and
> reading in the previous charge file. The curve starts off as expected,
> linear (ohmic conduction) but diverges quickly. In addition, I can't
> get the system to converge with applied voltages larger then ~0.2 V.
> Any input will be appreciated. Attached is the input file.
>
> Thanks   
>
> Inline image 2
>
>
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-- 
--
Dr. Gabriele Penazzi
BCCMS - University of Bremen

http://www.bccms.uni-bremen.de/
http://sites.google.com/site/gabrielepenazzi/
phone: +49 (0) 421 218 62337
mobile: +49 (0) 151 19650383

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