[DFTB-Plus-User] Gold Fermi Energy

[Gabriele Penazzi]

Hi Alessandro,

it's hard to give you a one-shot answer, for the following reason: in
principle, a robust parameterization should give consistent results
(i.e. a decent work function); in practice, as to do such a
parameterization for gold is very challenging, there may be parameters
out there tuned for one or another application but there's not any
"official" Au parameter on dftb.org yet I can refer to. If your
parameters have not been tested by someone else, you should do it yourself.

I am assuming you are working with SCC, as the non-scc case is quite
trivial. In SCC using the Fermi you get from your calculation should
ensure that you converge to a bulk gold with zero charge transfer, and I
would probably start from there. Then, whether for your particular case
the band alignment can still be decent for your investigation,
comparable with dft or even "better" for some lucky error cancellation,
I cannot know it. I think anyway that a "wrong" (meaning not consistent
with your lead calculation) Fermi level, if not too "wrong", will lead
to charge compensation in the gold buffers and give a rigid energy
shift, or at least this is what I saw in some systems. If this is the
case, qualitative results should be robust with respect to your choice
of Fermi level.

Best,
Gabriele



On 02/03/2015 12:39 PM, Alessandro Pirrotta wrote:
> Dear Gabriele,
>
> Thank you for your email. I have run the attached script and I get a
> gold Fermi energy of -2.9 eV.
> Do I want it to be close to the experimental value or do I take any
> value my parameters give me and use it for the transport calculation?
> The input files are attached.
>
> 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 <mailto:alessandro.pirrotta at chem.ku.dk>
>
> alessandro.pirrotta at gmail.com <mailto:alessandro.pirrotta at gmail.com>
>
> www.ki.ku.dk <http://www.ki.ku.dk/>
>
>
> On 3 February 2015 at 10:09, Gabriele Penazzi <penazzi at uni-bremen.de
> <mailto:penazzi at uni-bremen.de>> wrote:
>
>     Hi Alessandro,
>
>     you can calculate it with dftb itself, and be sure to be
>     consistent with your parameter set.
>     Anyway, if you have a "normal" junction with fermi level deep
>     between Homo-Lumo gap, I don't think it makes a huge difference
>     besides an overall shift, excess/defect charges should be
>     compensated in the gold buffers. But once you have one, be consistent.
>
>     Best,
>     Gabriele
>
>
>     On 02/03/2015 09:37 AM, Alessandro Pirrotta wrote:
>>     Dear DFTB+ community,
>>
>>     I would like to ask you if there is a correct value for the Fermi
>>     energy of gold.
>>     I am running an electron transport calculation of molecular
>>     junction with Au(111) and I am supposed to set the Fermi energy
>>     for the metal junction.
>>     I have found different values such -4.8 eV, -5.1 eV and -5.53 eV
>>     and I do not know on what basis I should pick one of them.
>>
>>     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 <tel:%2B45%2021%2018%2011%2090>
>>     MOB +45 52 81 23 41 <tel:%2B45%2052%2081%2023%2041>
>>
>>     alessandro.pirrotta at chem.ku.dk
>>     <mailto:alessandro.pirrotta at chem.ku.dk>
>>
>>     alessandro.pirrotta at gmail.com <mailto:alessandro.pirrotta at gmail.com>
>>
>>     www.ki.ku.dk <http://www.ki.ku.dk/>
>>
>>
>>
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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 <tel:%2B49%20%280%29%20421%20218%2062337>
>     mobile: +49 (0) 151 19650383 <tel:%2B49%20%280%29%20151%2019650383>
>
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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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