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? 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 >> >
