Top Page > Browsing
Work function calculations and the PAO cutoff radius
Date: 2017/12/15 23:18
Name: Konstantin Khromov   <k.yu.khromov@gmail.com>

Dear OpenMx users!

A'm trying to calculate the work function for the (100) surface in Molybdenum. For this purpose I've constructed a 1x1x5 slab periodic in x and y directions and having 10 atomic planes in z direction covered by about 1.5 nm vacuum region (approximately the same length as occupied by the atomic planes). The work function value is very sensitive to the PAO cutoff radius. The DFT_DATA13 database coming with opemnx contains the three version of PAO: Mp7.0.pao, Mo9.0.pao and Mo11.0.pao. While for the cutoff radii equal to 7 and a. u. I get underestimated, but at least reasonable by the order of magnitude values of work function equal to 2.9 and 3.7 eV respecitively, for the cutoff radius equal to 11 a. u. the work function value is about 30 eV, and both chemical potential and Hartree potential in the vacuum are very different from the case of 7 or 9 curoff radius. What may be so wrong with the the larger cutoff?

regargs,
Konstantin
メンテ
Page: [1]

Re: Work function calculations and the PAO cutoff radius ( No.1 )
Date: 2017/12/15 23:33
Name: Chi-Cheng Lee  <cclee.physics@gmail.com>

Hi Konstantin,

Could it be the problem already exists in bulk calculation? For example, are the
band structures of bulk consistent from different cutoff radii? If the band structure
of Mo11.0 shows some ghost bands, we are lucky to know it is due to the over completeness.
I have never calculated work function, but I guess adding some empty atoms in the vacuum
could help you get more accurate values.

Cheers,
Chi-Cheng
メンテ
Re: Work function calculations and the PAO cutoff radius ( No.2 )
Date: 2017/12/16 05:03
Name: Konstantin Khromov  <k.yu.khromov@gmail.com>

An update to my question.

The original question was related to openmx version 3.7 and Mo11.0.pao coming with the package.

Now I've recalculated the work function using openmx version 3.8 and Mo11.0.pao provided with the new version, keeping all the parameters exactly the same. The work function now is about 12 eV, much better that 30 eV, but still too large.

I actually tried introducing empty atoms into the vacuum region for Mp9.0.pao, resulted in less than 0.2 eV difference from the case with no empty spheres.
メンテ
Re: Work function calculations and the PAO cutoff radius ( No.3 )
Date: 2017/12/16 07:26
Name: Chi-Cheng Lee  <cclee.physics@gmail.com>

Hi Konstantin,

Have you checked the band structures of bulk or slab with different radii?
Are they very different or similar? I was guessing the longer radius could
give you a basis that is over complete. In that case, you should not trust the result.

Cheers,
Chi-Cheng

メンテ
Re: Work function calculations and the PAO cutoff radius ( No.4 )
Date: 2017/12/16 08:36
Name: T. Ozaki

Hi,

I think that the case of 11 a.u. is due to the overcompleteness of basis functions
which can be confirmed by an erratic band dispersion for the bulk calculation.

We have performed calculations of work function for metals before, and found that OpenMX
well reproduces the values comparable to those by plane-wave methods.
An example can be seen in the page 59 at

http://www.openmx-square.org/video_lec/OpenMX-Hands-on-2014Oct10.pdf

Adding a single ghost layer reaches almost convergent result, while 'no ghost'
underestimates the work function of Al(111) surface. For other metals, we confirmed
a similar behavior.

Regards,

TO
メンテ
Re: Work function calculations and the PAO cutoff radius ( No.5 )
Date: 2017/12/16 19:54
Name: Konstantin Khromov  <k.yu.khromov@gmail.com>

Hi, guys

Thanks a lot for your suggestions. I just want to clarify if a "ghost" is a synonym for an empty atom as described in the openmx manual?

Konstantin
メンテ
Re: Work function calculations and the PAO cutoff radius ( No.6 )
Date: 2017/12/16 21:29
Name: Chi-Cheng Lee  <cclee.physics@gmail.com>

Hi Konstantin,

I would consider "ghost" as "not real". When I mentioned ghost bands, I meant the bands not belonging to
the real band structure. The ghost layers means a layer not belonging to the real structure but just a basis.

Cheers,
Chi-Cheng
メンテ
Re: Work function calculations and the PAO cutoff radius ( No.7 )
Date: 2017/12/16 23:39
Name: Naoya Yamaguchi

Hi,

I also calculated the work function previously for M(111) surfaces (M=Al, Cu, Ag, Au, Pd), and attach a slide about it to the following URL for reference:
https://gist.github.com/Ncmexp2717/eceeac40c55153374fda4824e173720b/raw/7cfaa1fd89bf4418769777979b7a7d607d6c9dfe/slide_wf_reduced.pdf

I also confirmed that the values improves by using empty atom scheme for any case. And, I think two atomic layers are enough. In the calculations, only PAOs appropriate for bulk systems were used (e.g. 7.0 Bohr for Au). The calculated values were in agreement with experimental ones in the empty atom scheme (See the last page in the slides).

Regards,
Naoya Yamaguchi
メンテ

Page: [1]

Title (must) Move the thread to the top
Your Name (must)
E-Mail (must)
URL
Password (used in modification of the submitted text)
Comment (must)

   Save Cookie