[DFTB-Plus-User] DFTB-NEGF; SCC convergence with bias

[Gabriele Penazzi]

On 03/11/2015 11:47 PM, Michael Foster wrote:
> Hi,
>
> I'm trying to calculate the current (I) as a function of applied bias
> (V) for various molecules attached to metallic CNTs (currently working
> with 10,10); however, I'm having issues with SCC convergence. The
> system(s) converge no problem without a applied bias; however, when I
> apply a bias (e.g. 0.2 V for a ideal 10,10-CNT) the SCC will not
> converge. Attached is my dftb_pin.hsd file for a ideal 10,10-CNT with
> 0.2 V bias

Hi Mike,

convergence is often tricky. You can try the following:

1) Use smaller bias steps. Sometimes at a specific bias there may be
some physical reason for missing convergence (for example, a level
crosses the Fermi level) and you need to especially refine bias points
there around. I see you are reading the charge from previous
calculation, this is good.

2) Use finite temperature. This helps if a level needs to convergence to
a fractional occupation value.

3) Try smaller mixing parameters (e.g. 0.05).

Best,
Gabriele

>
> Thanks in advance for any help,
> Mike
>
>
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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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