[Pw_forum] Problem with pseudopotential

[Nicola Marzari]

Dear Izaak,


one of the graphs looks indeed very suspicious - it's the graph
named "planar-average-pbedrrkjus.pdf", but labeled inside
"Cu100 PP-van-ak 1vs2" (this is in itself is not a good sign :-)).

Make sure you perform two identical calculations, with  identical input 
files, and identical postprocessing, but only swap the pseudopotential
name - first for the rrkjus pseudo, then for the ak-converted van
pseudo.

Calculate the average of the planar avarage, and then the work function
(you could look at Phys. Rev. B 80, 235407 (2009) for an extensive
discussion of these issues) - and see if you still get incorrect results.

If you do, and everything else was absolutely identical, and one
calculation gives a result that is in the experimental ballpark, and
one gives a result that doesn't make sense, then the pseudopotential
has a problem, and you should report it.

Double check also that your structure is correct (plot it with
xcrysden). Only superficial comment on the input is that you might
need a bit more k-points and a bit less smearing for ultimate accuracy.

				nicola


On 3/29/11 12:44 AM, Izaak Williamson wrote:
> Dear all,
> I was trying to calculate the workfunction for Cu(100) surface. When I
> plotted the planar average of Vbare+VH as a function of z, I found that
> Vbare+VH at some points is higher than Vbare+VH at the vacuum level. I
> have attached the file (planar-average-pbedrrkjus.pdf). I am also
> attaching the input file Cu100.in <http://Cu100.in>. Does this mean that
> the pseudopotential (*Cu.pbe-d-rrkjus.UPF*
> <http://quantum-espresso.org/pseudo/1.3/UPF/Cu.pbe-d-rrkjus.UPF>) is
> wrong? Why does it behave like this?
> When I do the same calculation with *Cu.pbe-n-van_ak.UPF*
> <http://quantum-espresso.org/pseudo/1.3/UPF/Cu.pbe-n-van_ak.UPF>
> pseudopotential, then I get a reasonable graph
> (planar-average-pbevanak.pdf <http://planar-average-pbevanak.ps>). Any
> suggestions/explanations would be greatly appreciated.
> Thank you.
>
> --
> Izaak Williamson
> Research Assistant
> Physics Department
> Boise State University
>


-- 
----------------------------------------------------------------------
Prof Nicola Marzari    Department of Materials    University of Oxford
Chair of Materials Modelling  Director, Materials Modelling Laboratory
nicola.marzari at materials.ox.ac.uk     http://mml.materials.ox.ac.uk/NM