[Pw_forum] Work function issues

[Giuseppe Mattioli]

Dear all
If you do not want to bother with potential realignment in slab calcuations of WF you can use the (very nice) new implementation of the ESM method in 
a vacuum-slab-vacuum framework.

The usage is very simple

    assume_isolated = 'esm',
    esm_bc='bc1',

and you find in the outdir some prefix.esm1 file containing all the desired quantities (charge density, a variety of potentials) averaged along the z 
axis of the cell.

#z (A)  Tot chg (e/A)  Avg v_hartree (eV)  Avg v_local (eV)  Avg v_hart+v_loc (eV)

As the method decouple the slab along z you can also treat polar interfaces (e.g. gold electrode + polar SAM) and obtain two nice, different, flat 
asymptotic values of the potential on the two sides of the slab, without using any dipole correction.

HTH
Giuseppe

On Friday, April 22, 2016 04:51:18 PM Giovanni Cantele wrote:
> Maybe it is neither a poor pseudo potential choice nor a bug or user error.
> 
> Using for example Au.pbe-mt_fhi.UPF  I get
> 
> Fermi level ~ 3.30 eV
> vacuum level ~ 8.48eV
> 
> with a plot similar to what you attach in a follow-up e-mail.
> That corresponds to a ~ 5.17 gold work function, not that far from literature results, see, e.g., PHYSICAL REVIEW B 80, 235407 2009 .
> 
> Take care of slab thickness convergence issues as well as of the fact that a more accurate calculation might require a bulk crystal calculation,
> see details in the above reported reference.
> 
> Giovanni
> 
> > On 21 Apr 2016, at 17:57, Hepplestone, Steven <S.P.Hepplestone at exeter.ac.uk> wrote:
> > 
> > Dear all,
> > 
> > I am having difficulties with calculating the work function of various metals (Au and Pt in particular) using the X.pbe-mt_fhi.UPF and
> > X.pbe-n-nc.UPF pseudo potentials.  Unlike in the example in WorkFct_example in PP I am regularly getting a positive Fermi energy and a vacuum
> > level which is lower than the average level for the potential of the atoms.  Is this a case of poor pseudo potential choice, a bug or user error?
> > 
> > Any advice would be appreciated,
> > 
> > Kind regards
> > 
> > Steven
> > 
> > 
> > Dr. Steven Hepplestone
> > Physics
> > University of Exeter
> > Stocker Road
> > Exeter
> > EX4 4QL
> > Ext.: +44 (0)1392 723048
> > Int.: 3048
> > 
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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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