[Pw_forum] Doubt in workfunction example for Al100

Mon Mar 30 12:57:48 CEST 2015

Provided that you have a sufficient number of layers to guarantee in both sides a “bulk-like” region, you can choose the innermost layers.

But, because you have an interface, what is the quantity are you interested in? The interface barrier (in your case the Schottky barrier, because you have a metal-semiconductor
junction) or the work function? Consider that, in the latter case, because the two sides of the slab are different:
i) the vacuum level is different at the two sides, so you just choose the interplanar distance of the material you are interested in (either ZnO or Au)
ii) because  the vacuum level is different at the two sides, you must consider to add a correction for a “spurious” dipole introduced by boundary conditions, using         tefield=.true.
        dipfield=.true., and the related variables (see PW/DOC/INPUT_PW.txt for explanation) edit, eamp=0.D0, eopreg and examples

In the case you are instead interested in the interface barrier, you easily figure out that by choosing, as the window for the macroscopic average either the ZnO or the Au interplanar distance you get rid of microscopic oscillations only on one side. In this case, you can compute the averages with both windows, and plot them on the same plot. If needed, you might want to have a look at Fig. 6 of N.R. D’amico, et al,  J. Phys.: Condens. Matter 27 (2015) 015006 

Hope this helps,

    Giovanni

PS Warning: the ZnO orientation you are studying is polar, so the macroscopic average does not give you a constant value of the potential in the innermost part of the ZnO slab,
but a linearly varying one. There are examples in the literature on how the handle the electrostatic potential in polar slabs, see references in the above mentioned paper.

> On 30 Mar 2015, at 11:47, Bipul Rakshit <bipulrr at gmail.com> wrote:
> 
> Really thanks for your suggestion Giovanni,
> I just have few more doubts that if i want to find the work function of Au-ZnO Slab. I have created Au(111) and ZnO(0001) Slab. So it has an interface of Zn-Au and a vacuum of 10 Angstrom. I took 6 layers of Au and 4 double layers of ZnO. Then how to proceed.
> Means
> 1) Which two consecutive atomic planes I have to choose Au-Au, Au-Zn or the Zn-O planes. for the microscopic average calculation?
> 
> 2) Also in-order to choose the inner part of the slab, so that part is inside the Au-Slab or the ZnO Slab?
> 
> regards
> 
> 
> On Wed, Mar 18, 2015 at 5:02 PM, Giovanni Cantele <giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>> wrote:
> The average electrostatic potential you are calculating/plotting does show microscopic oscillations, revealing the atomic planes
> (plot the 2d column of reference/Al100.avg.out  as a function of the 1st one).
> 
> The calculation of the work function requires a “constant” energy level to compare the bulk and the slab calculation. For this purpose,
> you run a macroscopic average of the x-y averaged electrostatic potential. The window you choose for the macroscopic average
> is just the distance between two consecutive atomic planes (in a.u.).
> Because the input positions are in alat units, you get
> 
> (2.8284271247461898 - 2.1213203435596428) * 5.4235090117 = 3.835
> 
> In this way, microscopic oscillations with period 3.835 are averaged and a constant level (in the inner region of the slab) is obtained.
> 
> Concerning 17.8087, in order to get this constant value, you can choose any position in the inner part of the slab where the
> macroscopic average does not show significant variations.
> 
> Giovanni
> 
> 
>> On 18 Mar 2015, at 10:49, Bipul Rakshit <bipulrr at gmail.com <mailto:bipulrr at gmail.com>> wrote:
>> 
>> In espresso, there is an example to find the workfunction of Al. In the run_example, the input for the the macroscopic average is the following
>> cat > Al100.avg.in <http://al100.avg.in/> <<EOF
>> 1
>> Al100.pot
>> 1.D0
>> 1440
>> 3
>> 3.835000000
>> EOF
>> 
>> In this file the quantity "3.835" i saw in average.f90 as "awin         ! the size of the window for macroscopic averages"
>> 
>> So my doubt is how we can choose this no. Can we get the information from another file prerun file, like Al100.pot, or something else.
>> 
>> Also in run_example there is another quantity vSlab
>> 
>> vSlab=`grep "17.8087" Al100.avg.out | cut -d \  -f 10`
>> 
>> So how the value correspond to "17.8087" is assign as vSlab?
>> 
>> Kindly help me in this matter.
>> 
>> regards
>> -- 
>> Dr. Bipul Rakshit
>> Research Associate,
>> Institute of Physics (IOP),
>> Bhubaneswar- 751 005
>> Orissa 
>> India
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> -- 
> 
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
> 
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009 <http://www.researcherid.com/rid/A-1951-2009>
> Web page: http://people.na.infn.it/~cantele <http://people.na.infn.it/~cantele>
> 
> 
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> 
> 
> 
> -- 
> Dr. Bipul Rakshit
> Research Associate,
> Institute of Physics (IOP),
> Bhubaneswar- 751 005
> Orissa 
> India
> _______________________________________________
> Pw_forum mailing list
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> http://pwscf.org/mailman/listinfo/pw_forum

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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