Dear Ahmed,
I calculated the Ef of graphene|Cu(111), the value is -3.67eV. But the
band structure is correct, according to the former papers. So Can I say that
my calculation is reasonable ? Best wishes.
Zhendong Guo
2010/12/26 Ahmed Huzayyin <[email protected]>
> Hi Everyone,
>
> I agree with Andrei comment below, the Ef generated by SIESTA cannot be
> used to calculate the work function. To determine the work function you need
> to apply the "Bulk Plus Band LineUp" method. For details please see "Van de
> Walle and Martin, 1987, Phys Rev B, no. 35, pp.8154". The method involves
> solving bulk system and a slab to pin down the *relative* energy between
> the vacuum and Ef (as Andrei mentioned below "a difference energy"). In
> general DFT and I believe SIESTA can reproduce the work function of metals
> with good accuracy (with 5% or so).
>
> Thanks
> Ahmed
>
> Ahmed Huzayyin
> PhD Candidate
> ECE Department
> University of Toronto
>
>
> ------------------------------
> *From:* "[email protected]" <[email protected]>
> *To:* [email protected]
> *Sent:* Sat, December 25, 2010 12:04:56 PM
> *Subject:* Re: Re: [SIESTA-L] Metal Fermi Levels
>
> > Dear apostnik,
> > Thanks for your instruction on this issue.
> > As you have said,we should find out the vacuum energy and then use the
> got
> > Fermi level from SIESTA to subtract it and this is the work function.
> >
> > Am I right?
>
> This is not exactly what I wanted to say;
> anyway I am not an expert in calculating work functions.
> There should be enough works done on this subject before,
> not necessarily with Siesta.
> In any case, the problem should reduce to extracting some energy difference
> between reasonably selected reference cases.
> This granted,
> the absolute numbers of these energies would not play a role.
>
> I intended to comment only on this narrow issue, being worried
> that the colleagues tended to take an absolute value of Ef,
> provided by Siesta, for a hint whether the calculation is good or bad.
> In fact you cannot decide based on this information only.
>
> Best regards
>
> Andrei Postnikov
>
>
> >
> > Thanks a lot.
> >
> > 2010-12-25
> >
> >
> >
> > Guangping Zhang
> >
> >
> >
> > 发件人: [email protected]
> > 发送时间: 2010-12-25 15:46
> > 主 题: Re: [SIESTA-L] Metal Fermi Levels
> > 收件人: [email protected]
> >
> >
> >
> > Dear BR/Yujia / Ronaldo,
> > it must have been discussed already a couple of times, but still:
> > The absolute value of the Fermi energy as it comes out of the calculation
> > is largely method-dependent. It makes sense to discuss its correct /
> wrong
> > position with respect to the band structure, but not relative to
> > zero level of energy, that is, typically, a somehow
> > averaged value of some potential. (For instance, in a calculation with
> > a FLAPW method, a "typical" Fermi energy might be +6 eV or so, so what?).
> >
> > In order to get the work function, you need to make comparison
> > with the potential in the vacuum far away from your sample.
> > The values from bulk calculation don't tell you much about this,
> > so be careful.
> >
> > Best regards
> >
> > Andrei Postnikov
> >
> >
> >> Dear BR/Yujia,
> >>
> >> The values of IP and EA, and of the work function as a consequence, is
> >> sensitive to the confinement imposed on basis orbitals. Using the
> >> default
> >> value of energy shift (0.01 Ry)
> >> I also obtained a value of fermi level for Au(111), -4.1eV, which
> >> greatly
> >> differs from those previously reported. I have obtained a better result,
> >> -5.1eV, decreasing the value of energy shift to 0.001 Ry. As it is
> >> possible
> >> to see in Nanotechnology *21* (2010) 065705, the value of Au(111) fermi
> >> level converges to that obtained using plane waves (-5.25eV) in the
> >> limite
> >> of very small basis set confinement.
> >>
> >> Best,
> >>
> >> Ronaldo
> >>
> >> On Fri, Dec 24, 2010 at 5:33 AM, zjuyangyj <[email protected]> wrote:
> >>
> >>> Dear all,
> >>> Recently I am calculating the work functions or fermi levels of
> >>> different
> >>> metals. However, my results seem to be incorrect. For example, I got
> >>> the
> >>> fermi level for Au as -3.68eV, which greatly differs from previous
> >>> theoretically or experimentally reported values, which range from
> >>> -4.8eV
> >>> to
> >>> -5.3eV. Also I got the fermi level for Pt as -3.99eV, also largely
> >>> differing
> >>> from correct values.
> >>>
> >>> I want to know what might be the possible reasons for incorrect fermi
> >>> levels, and when calculating fermi levels, what are the
> >>> important/relevant parameters? I am calculating very thin metal films
> >>> (tens
> >>> of atom layers), and I found the number of layers an important
> >>> parameter.
> >>> Also I want to know whether the fermi levels of bulk and thin film
> >>> metal
> >>> differs a lot.
> >>>
> >>> Thank you for your attention.
> >>>
> >>> BR/Yujia
> >>>
> >>
>
>
>
--
Zhendong Guo
Institute of Microelectronics and Optoelectronics, Room 516,
Dept. of Information Science & Electronic Engineering
Zhejiang University
Hangzhou, China, 310027
Phone: 15168215062
Email: [email protected]
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