[Pw_forum] Problem with pseudopotential

[Nicola Marzari]

Dear Izaak,


it seems that in Cu.pbe-d-rrkjus.UPF the average electrostatic potential
inside the slab (i.e. the average over one layer of the planar average)
would be higher than the vacuum level, so on electrostatic 
considerations a test charge would want to run away. So, I'm very 
baffled. Any one else has some suggestion? The two input files do look
identical.

The fermi energy that you print is the one given by the slab calculation 
(not really a good choice, unless you have a thick slab)
or is given by calculating in bulk cu the position of the fermi energy 
with respect to the layer-average of the planar avarage, and then using
that info in the slab calculation to position the fermi energy of the 
bulk, and obtain the work function?

Last - a 14% is the last of the worries - LDA and GGA seem to be all 
over the place (have a look at the paper I had cited).

				nicola



On 3/30/11 4:53 PM, Izaak Williamson wrote:
> First of all, thank you so much for your replies.
>
> One more question: in the pbedrrkjus plot, there are maxima at the
> location of each atomic layer whereas the pbevanak plot has minima. What
> would cause this? Is it a problem?
>
>
> Both the calculations were done using exactly the same parameters but
> different pseudopotentials. I get the following values for workfunctions.
> Cu.pbe-d-rrkjus.UPF ---> 3.956405463 eV
> Cu.pbe-n-van_ak.UPF ---> 4.042282570 eV
> Experimental value ---> 4.59 eV
>
> I know that DFT-GGA calculations can underestimate the workfunctions of
> metal surfaces, but are these acceptable values (almost a 14% error)?
>
> Thank you again for all your help.
>
>
> --
> 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